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PubMed2002

In vivo assessment of the Tat signal peptide specificity in Escherichia coli.

Tat- and Sec-targeting signal peptides are specific for the cognate Tat or Sec pathways. Using two reporter proteins, the specificity and convertibility of a Tat signal peptide were assessed in vivo. The specific substitutions by RK, KR and KK for the RR motif of the TorA signal peptide had no effect on the exclusive Tat-dependent export of colicin V (ColV). By introducing multiple substitutions in a typical Tat signal peptide, altered signal peptides lacking the twin-arginine motif were obtained. Interestingly, some of these signal peptides preserved Tat-pathway targeting capacity, but resulted in a loss of exclusivity. In addition, further increasing the hydrophobicity of the n-region without modifying the h-region converted the Tat signal peptides to Sec signal peptides in the ColV transport. Replacement of positively charged residues in the c-region also abolished the Tat-exclusive targeting of ColV or green fluorescent protein (GFP), but the folded GFP could be transported only through the Tat pathway. These results strongly suggest that the overall hydrophobicity of the n-region is one of the determinants of Tat-targeting exclusivity.

Amino Acid Sequence↗
PubMed1988

Defective Escherichia coli signal peptides function in yeast.

To investigate structural characteristics important for eukaryotic signal peptide function in vivo, a hybrid gene with interchangeable signal peptides was cloned into yeast. The hybrid gene encoded nine residues from the amino terminus of the major Escherichia coli lipoprotein, attached to the amino terminus of the entire mature E. coli beta-lactamase sequence. To this sequence were attached sequences encoding the nonmutant E. coli lipoprotein signal peptide, or lipoprotein signal peptide mutants lacking an amino-terminal cationic charge, with shortened hydrophobic core, with altered potential helicity, or with an altered signal-peptide cleavage site. These signal-peptide mutants exhibited altered processing and secretion in E. coli. Using the GAL10 promoter, production of all hybrid proteins was induced to constitute 4-5% of the total yeast protein. Hybrid proteins with mutant signal peptides that show altered processing and secretion in E. coli, were processed and translocated to a similar degree as the non-mutant hybrid protein in yeast (approximately 36% of the total hybrid protein). Both non-mutant and mutant signal peptides appeared to be removed at the same unique site between cysteine 21 and serine 22, one residue from the E. coli signal peptidase II processing site. The mature lipo-beta-lactamase was translocated across the cytoplasmic membrane into the yeast periplasm. Thus the protein secretion apparatus in yeast recognizes the lipoprotein signal sequence in vivo but displays a specificity towards altered signal sequences which differs from that of E. coli.

Amino Acid Sequence↗
PubMed1987

Mutational alterations affecting the export competence of a truncated but fully functional maltose-binding protein signal peptide.

The wild-type maltose-binding protein (MBP) signal peptide is 26 amino acids in length. A mutationally altered MBP signal peptide has been previously described that is missing one of the basic residues from the hydrophilic segment and seven residues from the hydrophobic core; however, it still facilitates MBP secretion to the periplasm at a rate and efficiency comparable to those of the wild-type structure. Thus, this truncated signal peptide (designated the R2 signal peptide) must retain all of the essential features required for proper export function. In this study, alterations were obtained in the R2 signal peptide that resulted in an export-defective MBP. For the first time, signal sequence mutations were obtained that resulted in the synthesis of a totally export-defective MBP. As was previously the case for the wild-type signal peptide, the introduction of either charged residues or helix-breaking proline residues adversely affected export function. Despite these similarities, the position of these alterations within the R2 signal peptide, their relative effects on MBP secretion and processing, and an analysis of the ability of various extragenic prl mutations to suppress the secretion defects provide additional insight into the minimal requirements for a functional MBP signal peptide.

ATP-Binding Cassette Transporters↗
PubMed1985

Dual functions of the signal peptide in protein transfer across the membrane.

Most secretory proteins in both prokaryotic and eukaryotic cells are synthesized from a precursor with an amino-terminal extension of 20 to 25 amino acid residues called a signal peptide. These signal peptides are removed during translocation of the secretory proteins across the membrane. When two precursor structures are fused, the internalized second signal peptide was found to exert two different roles, depending upon either the distance between the two signal peptides, or whether the first signal peptide functions cotranslationally or posttranslationally. One role is to function as the usual signal peptide to translocate the protein downstream of the internal signal peptide. The other role is to function as a stop-transfer signal to create a transmembrane protein with the second signal peptide anchoring the protein in the membrane.

Bacterial Outer Membrane Proteins↗
PubMed2005

Signal peptide hydrophobicity is critical for early stages in protein export by Bacillus subtilis.

Signal peptides that direct protein export in Bacillus subtilis are overall more hydrophobic than signal peptides in Escherichia coli. To study the importance of signal peptide hydrophobicity for protein export in both organisms, the alpha-amylase AmyQ was provided with leucine-rich (high hydrophobicity) or alanine-rich (low hydrophobicity) signal peptides. AmyQ export was most efficiently directed by the authentic signal peptide, both in E. coli and B. subtilis. The leucine-rich signal peptide directed AmyQ export less efficiently in both organisms, as judged from pulse-chase labelling experiments. Remarkably, the alanine-rich signal peptide was functional in protein translocation only in E. coli. Cross-linking of in vitro synthesized ribosome nascent chain complexes (RNCs) to cytoplasmic proteins showed that signal peptide hydrophobicity is a critical determinant for signal peptide binding to the Ffh component of the signal recognition particle (SRP) or to trigger factor, not only in E. coli, but also in B. subtilis. The results show that B. subtilis SRP can discriminate between signal peptides with relatively high hydrophobicities. Interestingly, the B. subtilis protein export machinery seems to be poorly adapted to handle alanine-rich signal peptides with a low hydrophobicity. Thus, signal peptide hydrophobicity appears to be more critical for the efficiency of early stages in protein export in B. subtilis than in E. coli.

Alanine↗
PubMed2002

A novel Ala(-3)Thr mutation in the signal peptide of human luteinizing hormone beta-subunit: potentiation of the inositol phosphate signalling pathway and attenuation of the adenylate cyclase pathway by recombinant variant hormone.

Upon screening for polymorphisms in the human luteinizing hormone beta-subunit (LH beta) gene, we discovered a novel mutation in the LH beta signal peptide with functional consequences for signal transduction in mouse Leydig tumour cells (mLTC-1). This G(52)A point mutation in exon 2 of the LH beta gene, detected in heterozygous form in several normal DNA samples, caused an Ala(-3)Thr amino acid substitution. Recombinant forms of wild-type (WT) and Ala(-3)Thr variant (V) LH were produced in human embryonic kidney (HEK) 293 cells and purified. The immunoreactivities of the recombinant LH were determined by immunofluorometric assays and in-vitro bioactivities in mLTC-1 cells were assessed by using cAMP, progesterone and inositol trisphosphate (IP(3)), and activation of mitogen-activated protein kinase (MAPK) as end-points. Whereas both LH forms stimulated progesterone production and MAPK in similar fashion, WT-LH was more potent in stimulating cAMP, and V-LH was more potent in stimulating IP(3) generation. Both LH forms bound to LH receptors with similar affinities. No evidence was found for influence of the signal peptide mutation on efficacy of alpha- and beta-subunit dimerization. Sequencing of the recombinant V-LH beta protein also revealed that the mutation did not interfere with signal peptide cleavage. In summary, the present findings indicate that the Ala(-3)Thr mutation in the LH beta-subunit signal peptide has functional consequences, in the form of dissociation of stimulatory potency for different signal transduction pathways in vitro.

Adenylyl Cyclases↗
PubMed2005

Alteration in the IL-2 signal peptide affects secretion of proteins in vitro and in vivo.

BACKGROUND: Although hundreds of different signal peptides have now been identified, few studies have examined the factors enabling signal peptides to augment secretion of mature proteins. Signal peptides, located at the N-terminus of nascent secreted proteins, characteristically have three domains: (1) a basic domain at the N-terminus, (2) a central hydrophobic core, and (3) a carboxy-terminal cleavage region. In this study, we investigated whether alterations in the basic and/or the hydrophobic domains of a commonly used signal peptide from interleukin-2 (IL-2) affected secretion of two proteins: placental alkaline phosphatase (AP) and endostatin. METHODS: A series of modifications in the basic and/or hydrophobic domains of the IL-2 signal peptide were made by polymerase chain reaction with endostatin or AP plasmids as templates. Transfection of wild-type or modified IL-2 signal peptides fused in-frame with endostatin or AP were done with Superfect in vitro or by the hydrodynamic method in vivo. RESULTS: Increasing both the basicity and hydrophobicity of the signal peptide augmented the secretion of AP and endostatin by approximately 2.5- and 3.5-fold, respectively, from MDA-MB-435 cells in vitro. Over a range of DNA concentrations and times, the most effective IL-2 signal peptide increased AP levels in the medium compared to the wild-type IL-2 signal peptide. Comparable results from these modified IL-2 signal peptides were found to increase AP levels in the medium from bovine aortic endothelial cells. Moreover, the combined changes in basic and hydrophobic domains of the IL-2 signal peptide augmented serum levels of endostatin and placental AP by 3-fold when the optimal plasmid constructs were injected in vivo. CONCLUSIONS: Modification of the IL-2 signal peptide augments protein secretion both in vitro and in vivo. As a result, optimizing the signal peptide should be considered for increasing the therapeutic levels of secreted proteins.

Alkaline Phosphatase↗
PubMed1994

Stability and function of the signal peptide of the pCloDF13-derived bacteriocin release protein.

The pCloDF13-derived bacteriocin release protein (BRP) is synthesized as a prelipoprotein with a signal peptide which remains stable after processing. This signal peptide accumulates in the cytoplasmic membrane and is, together with the mature BRP, required for efficient release of cloacin DF13. We investigated the structural requirements for stability of the BRP signal peptide by constructing hybrid signal peptides consisting of parts of the BRP and Lpp signal peptides. Signal peptide stability was investigated by pulse-labelling and pulse-chase experiments. To study the functioning of the BRP signal peptide, the hybrid constructs were tested for their ability to promote BRP-mediated cloacin DF13-release and their ability to affect the viability of the host cells. The results obtained suggest that the N-terminal part of the BRP signal peptide together with the C-terminal alanine residue are important for stability. When expressed as a separate entity, all mutant signal peptides that contain a part of the BRP signal peptide are capable of affecting cell viability. The results indicated a possible correlation between stability of the BRP signal peptide and cloacin DF13-release.

Alanine↗
PubMed1987

Wild type and mutant signal peptides of Escherichia coli outer membrane lipoprotein interact with equal efficiency with mammalian signal recognition particle.

The signal peptide of the outer membrane lipoprotein (OMLP) of Escherichia coli was shown to be capable of promoting protein translocation across mammalian microsomal membranes in vitro. We assayed translocation of a fusion protein containing the OMLP signal peptide and nine amino acids of OMLP fused in frame to beta-lactamase. The efficiency with which the mammalian translocation machinery recognizes and accepts the OMLP signal peptide as substrate is indistinguishable from that of mammalian secretory proteins. Upon translocation mammalian signal peptidase processes the pre-OMLP-beta-lactamase protein at different sites than are utilized in vivo by E. coli OMLP signal peptidase (signal peptidase II) but that can be predicted as mammalian signal peptidase cleavage sites. Mutants in the OMLP signal peptide were tested for their ability to promote translocation of the fusion protein in this assay system. It has been shown previously that mutants in the positively charged amino acids at the amino terminus of the signal peptide severely delay the translocation of OMLP in vivo in E. coli. However, these mutants had no detectable effect either on signal recognition by mammalian signal recognition particle or on the efficiency of translocation itself.

Amino Acid Sequence↗
PubMed1998

Species-specificity in endoplasmic reticulum signal peptide utilization revealed by proteins from Trypanosoma brucei and Leishmania.

N-Terminal signal peptides direct secretory and most membrane proteins into the exocytic pathway at the endoplasmic reticulum. Signal sequences can function across kingdoms. However, our attempts at translocating variant surface glycoprotein (VSG) 117, VSG MVAT7, VSG 221 and BiP from Trypanosoma brucei and gp63 from Leishmania chagasi into canine pancreas microsomes failed. On replacing the signal peptide of VSG 117 with that from yeast prepro-alpha-mating factor (ppalphaMF) the chimaeric protein was imported, indicating that the signal sequence of VSG 117 was incompatible with the protein-import machinery of mammalian microsomes. Replacement of the gp63-h-region with a hybrid composed of the N-terminal nine residues from the h-region of gp67 from Autographa californica nuclear polyhedrosis virus and the C-terminal 10 residues from the h-region of gp63 from L. major produced a functional signal peptide. Thus, the h-region of kinetoplastid signal peptides appears to be the subdomain that is non-functional at the mammalian translocon. The calculated biophysical properties and computed discriminant scores (predictive of importability of signal peptides into mammalian microsomes) of the kinetoplastid signal sequences nevertheless are similar to those of ppalphaMF and Escherichia coli beta-lactamase both of which were imported. These signal peptides are the first collection from one biological family that have been found to fail to function across a species barrier. They indicate that signal peptides are not as universally interchangeable as previously believed. Intriguingly, endoplasmic reticulum signal peptides from Leishmania and Crithidia fasciculata are reminiscent of signal peptides from Gram-positive bacteria.

Amino Acid Sequence↗
PubMed1990

Residues flanking the COOH-terminal C-region of a model eukaryotic signal peptide influence the site of its cleavage by signal peptidase and the extent of coupling of its co-translational translocation and proteolytic processing in vitro.

The polar, COOH-terminal c-region of signal peptides has been considered to be most important for influencing the efficiency and fidelity of signal peptidase cleavage while the hydrophobic core or h-region appears indispensable for initiating translocation. To identify structural features of residues flanking the c-region that influence the fidelity and efficiency of signal peptidase cleavage as well as co-translational translocation, we introduced six amino acid substitutions into the COOH terminus of the hydrophobic core and seven substitutions at the NH2 terminus of the mature region (the +1 position) of a model eukaryotic preprotein-human pre(delta pro)apoA-II. This preprotein contains several potential sites for signal peptidase cleavage. The functional consequences of these mutations were assayed using an in vitro co-translational translocation/processing system and by post-translational cleavage with purified, detergent-solubilized, hen oviduct signal peptidase. The efficiency of translocation could be correlated with the hydrophobic character of the residue introduced at the COOH terminus of the h-region. Some h/c boundary mutants underwent co-translational translocation across the microsomal membrane with only minimal cleavage yet they were cleaved post-translationally by hen oviduct signal peptidase more efficiently than other mutants which exhibited a high degree of coupling of co-translational translocation and cleavage. These data suggest that features at the COOH terminus of the h-domain can influence "presentation" of the cleavage site to signal peptidase. The +1 residue substitutions had minor effects on the extent of co-translational translocation and processing. However, these +1, as well as h/c boundary mutations, had dramatic effects on the site of cleavage chosen by signal peptidase, indicating that residues flanking the c-region of this prototypic eukaryotic signal peptide can affect the fidelity of its proteolytic processing. The site(s) selected by canine microsomal and purified hen oviduct signal peptidase were very similar, suggesting that "intrinsic" structural features of this prepeptide can influence the selectivity of eukaryotic signal peptidase cleavage, independent of the microsomal membrane and associated translocation apparatus.

Amino Acid Sequence↗
PubMed2005

Signal peptide cleavage and internal targeting signals direct the hepatitis C virus p7 protein to distinct intracellular membranes.

The hepatitis C virus (HCV) p7 protein forms an amantadine-sensitive ion channel required for viral replication in chimpanzees, though its precise role in the life cycle of HCV is unknown. In an attempt to gain some insights into p7 function, we examined the intracellular localization of p7 using epitope tags and an anti-p7 peptide antibody, antibody 1055. Immunofluorescence labeling of p7 at its C terminus revealed an endoplasmic reticulum (ER) localization independent of the presence of its signal peptide, whereas labeling the N terminus gave a mitochondrial-type distribution in brightly labeled cells. Both of these patterns could be visualized within individual cells, suggestive of separate pools of p7 where the N and C termini differed in accessibility to antibody. These patterns were disrupted by preventing signal peptide cleavage. Subcellular fractionation revealed that p7 was enriched in a heavy membrane fraction associated with mitochondria as well as normal ER-derived microsomes. The complex regulation of the intracellular distribution of p7 suggests that p7 plays multiple roles in the HCV life cycle either intracellularly or as a virion component.

Cell Line↗
PubMed1991

Effect of OmpA signal peptide mutations on OmpA secretion, synthesis, and assembly.

In previous investigations, we have examined the effect of OmpA signal peptide mutations on the secretion of the two heterologous proteins TEM beta-lactamase and nuclease A. During these studies, we observed that a given signal peptide mutation could affect differentially the processing of precursor OmpA-nuclease or precursor OmpA-lactamase. This observation led us to further investigate the influence of the mature region of a precursor protein on protein export. Preexisting OmpA signal peptide mutations of known secretion phenotype when directing heterologous protein export (nuclease A or beta-lactamase) were fused to the homologous mature OmpA protein. Four signal peptide mutations that have previously been shown to prevent export of nuclease A and beta-lactamase were found to support OmpA protein export, albeit at reduced rates. This remarkable retention of export activity by severely defective precursor OmpA signal peptide mutants may be due to the ability of mature OmpA to interact with the cytoplasmic membrane. In addition, these same signal peptide mutations can affect the level of OmpA synthesis as well as its proper assembly in the outer membrane of Escherichia coli. Two signal peptide mutations dramatically stimulate the rate of precursor OmpA synthesis three- to fivefold above the level observed when a wild-type signal peptide is directing export. The complete removal of the OmpA signal peptide does not result in increased OmpA synthesis. This finding suggests that the signal peptide mutations function positively to stimulate OmpA synthesis, rather than bypass a down-regulatory mechanism effected by a wild-type signal peptide. Overproduction of wild-type precursor OmpA or precursors containing signal peptide mutations which lead to relatively minor kinetic processing defects results in accumulation of an improperly assembled OmpA species (imp-OmpA). In contrast, signal peptide mutations which cause relatively severe processing defects accumulate no or only small quantities of imp-OmpA. All mutations result in equivalent levels of properly assembled OmpA. Thus, a strong correlation between imp-OmpA accumulation and cell toxicity was observed. A mutation in the mature region of OmpA which prevents the proper outer membrane assembly of OmpA was suppressed when export was directed by a severely defective signal peptide. These findings suggest that signal peptide mutations indirectly influence OmpA assembly in the outer membrane by altering both the level and rate of OmpA secretion across the cytoplasmic membrane.

Amino Acid Sequence↗
PubMed1993

Efficient production of Bacillus stearothermophilus alpha-amylase in Bacillus brevis by altering its signal peptide.

To investigate the role of signal peptides in extracellular production in Bacillus brevis, the Bacillus stearothermophilus alpha-amylase signal peptide was systematically altered and the effects were analyzed in B. brevis. Efficient extracellular production of the amylase in B. brevis was accomplished either by introducing point mutations at positions between -6 and -4 or by replacing the whole signal peptide with that of B. brevis middle wall protein.

Amino Acid Sequence↗
PubMed2004

A combined transmembrane topology and signal peptide prediction method.

An inherent problem in transmembrane protein topology prediction and signal peptide prediction is the high similarity between the hydrophobic regions of a transmembrane helix and that of a signal peptide, leading to cross-reaction between the two types of predictions. To improve predictions further, it is therefore important to make a predictor that aims to discriminate between the two classes. In addition, topology information can be gained when successfully predicting a signal peptide leading a transmembrane protein since it dictates that the N terminus of the mature protein must be on the non-cytoplasmic side of the membrane. Here, we present Phobius, a combined transmembrane protein topology and signal peptide predictor. The predictor is based on a hidden Markov model (HMM) that models the different sequence regions of a signal peptide and the different regions of a transmembrane protein in a series of interconnected states. Training was done on a newly assembled and curated dataset. Compared to TMHMM and SignalP, errors coming from cross-prediction between transmembrane segments and signal peptides were reduced substantially by Phobius. False classifications of signal peptides were reduced from 26.1% to 3.9% and false classifications of transmembrane helices were reduced from 19.0% to 7.7%. Phobius was applied to the proteomes of Homo sapiens and Escherichia coli. Here we also noted a drastic reduction of false classifications compared to TMHMM/SignalP, suggesting that Phobius is well suited for whole-genome annotation of signal peptides and transmembrane regions. The method is available at as well as at

Membrane Proteins↗
PubMed2000

Increase in Hydrophobicity of Signal Peptide Enhances Secretion of Penicillin G Acylase.

An artificial strong hydrophobic signal peptide (ASP), containing ten leucines in tandem in the hydrophobic core, was utilized to replace the wild type signal peptide (WTSP) of penicillin G acylase (PAC), by the fusion to its 4 pro site. PAC expression plasmids, including pKKpacdeltaSP, pKKpacWTSP, pKKpacASP, pETpacWTSP and pETpacASP, were constructed. The length and the amino- and carboxyl-terminus amino acid composition of ASP and WTSP were kept identical. The activity assay and Western-blotting analysis were used to study the effect of ASP and WTSP on the secretion of PAC in tac, T7 and dissolved-oxygen regulation expression systems, respectively. Lack of signal peptide in pKKpacdeltaSP resulted in the accumulation of 91 kD PAC precursor (without signal peptide, but with the space peptide between alpha-subunit and beta-subunit) in the cytosol, indicating that the secretion of PAC depends on the signal peptide. In BL21(pKKpacASP) cells, the PAC activity and proprecursor (with signal peptide and space peptide) processing capacity were increased by about 54% and 38.5%, respectively, in comparison with BL21(pKKpacWTSP) cells. Compared with BL21(DE3) (pETpacWTSP), however, the PAC activity and proprecursor processing capacity in BL21(DE3) (pETpacASP) were enhanced by about 69% and 43.5%, respectively. The PAC activity expressed from pETpacASP was about 67% more than that from pETpacWTSP in the dissolved-oxygen-regulated expression system GJ100. Resulting from the strong hydrophobicity of ASP, therefore, the PAC activity and proprecursor processing capacity were increased by about 63% and 41% on average, respectively, in comparison with WTSP. In conclusion, the increase in hydrophobicity of the signal peptide hydrophobic core enhanced the secretion of penicillin G acylase.

Journal Article↗
PubMed1990

Structural features in the NH2-terminal region of a model eukaryotic signal peptide influence the site of its cleavage by signal peptidase.

The 20-amino acid signal peptide of human pre (delta pro)apolipoprotein A-II contains the tripartite domain structure typical of eukaryotic prepeptides, i.e. a positively charged NH2-terminal (n) region, a hydrophobic core (h) region, and a COOH-terminal polar domain (c region). This signal sequence has multiple potential sites for cotranslational processing making it an attractive model for assessing the consequences of systematic structural alterations on the site selected for signal peptidase cleavage. We previously analyzed 40 mutant derivatives of this model preprotein using an in vitro translation/canine microsome processing assay. The results showed that the position of the boundary between the h and c regions and properties of the -1 residue are critical in defining the site of cotranslational cleavage. To investigate whether structural features in the NH2-terminal region of signal peptides play a role in cleavage specificity, we have now inserted various amino acids between the positively charged n region (NH2-Met-Lys) and the h region of a "parental" pre(delta pro)apoA-II mutant that has roughly equal cleavage between Gly18 decreases and Gly20 decreases. Movement of the n/h boundary toward the NH2 terminus results in a dramatic shift in cleavage to Gly18 decreases. Replacement of the Lys2 residue with hydrophilic, negatively charged residues preserves the original sites of cleavage. Replacement with a hydrophobic residue causes cleavage to shift "upstream." Simultaneous alteration of the position of n/h and h/c boundaries has an additive effect on the site of signal peptidase cleavage. None of these mutations produced a marked decrease in the efficiency of in vitro cotranslational translocation or cleavage. However, in sequence contexts having poor signal function, introduction of hydrophobic residues between the n and h regions markedly improved the efficiency of translocation/processing. We conclude that the position of the n/h boundary as well as positioning of the h/c boundary affects the site of cleavage chosen by signal peptidase.

Amino Acid Sequence↗
PubMed2000

Signal peptide determinants of SecA binding and stimulation of ATPase activity.

A signal peptide is required for entry of a preprotein into the secretory pathway, but how it functions in concert with the other transport components is unknown. In Escherichia coli, SecA is a key component of the translocation machinery found in the cytoplasm and at membrane translocation sites. Synthetic signal peptides corresponding to the wild type alkaline phosphatase signal sequence and three sets of model signal sequences varying in hydrophobicity and amino-terminal charge were generated. These were used to establish the requirements for interaction with SecA. Binding to SecA, modulation of SecA conformations sensitive to protease, and stimulation of SecA-lipid ATPase activity occur with functional signal sequences but not with transport-incompetent ones. The extent of SecA interaction is directly related to the hydrophobicity of the signal peptide core region. For signal peptides of moderate hydrophobicity, stimulation of the SecA-lipid ATPase activity is also dependent on amino-terminal charge. The results demonstrate unequivocally that the signal peptide, in the absence of the mature protein, interacts with SecA in aqueous solution and in a lipid bilayer. We show a clear parallel between the hierarchy of signal peptide characteristics that promote interaction with SecA in vitro and the hierarchy of those observed for function in vivo.

Adenosine Triphosphatases↗