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Biomedical subjects

P Gros

Publications and source records attributed to P Gros.

At least 127 records · Page 7Linked to original sources

Functional complementation of the yeast divalent cation transporter family SMF by NRAMP2, a member of the mammalian natural resistance-associated macrophage protein family.

The mammalian NRAMP gene family has two members, NRAMP1 and NRAMP2 that encode integral membrane proteins. Nramp1 is expressed exclusively in macrophages where it is found in the phagosomal membrane, and NRAMP1 mutations cause susceptibility to infection by abrogating the capacity of macrophages to control intracellular microbial replication. Nramp2 is highly similar to Nramp1, but is expressed in several tissues and cell types. The Nramp protein family is remarkably conserved throughout evolution, and recent data suggest that the mammalian Nramp2 and the yeast homologues Smf1 and Smf2 transport divalent cations. We tested whether structural similarity between the mammalian Nramp and the yeast Smf proteins results in functional complementation in yeast. Wild-type and mutant variants of the Nramp1 and Nramp2 proteins were expressed in a yeast mutant bearing null alleles at the SMF1 and SMF2 loci, and complementation of the phenotypes of this yeast mutant was investigated. Nramp2, but not Nramp1, was found to complement hypersensitivity to EGTA of the smf1/smf2 mutant under oxidative stress conditions (methyl viologen). We also observed that the smf1/smf2 double mutant is hypersensitive to growth at alkaline pH (pH 7.9) and that Nramp2 could complement this phenotype as well. Complementation by Nramp2 was specific and required a functional protein as independent mutations in residues highly conserved in all members of the Nramp family abrogated Nramp2 complementation. Since Mn2+ was the only divalent cation capable of completely suppressing both the EGTA and pH phenotypes, our results suggest that Nramp2 can transport Mn2+ in yeast.

Amino Acid Sequence↗

The C-terminal subdomain makes an important contribution to the DNA binding activity of the Pax-3 paired domain.

The recognition of DNA targets by Pax-3 is achieved through the coordinate use of two distinct helix-turn-helix-based DNA-binding modules: a paired domain, composed of two structurally independent subdomains joined by a short linker, and a paired-type homeodomain. In mouse, the activity of the Pax-3 paired domain is modulated by an alternative splicing event in the paired domain linker region that generates isoforms (Q+ and Q-) with distinct C-terminal subdomain-mediated DNA-binding properties. In this study, we have used derivatives of a classical high affinity paired domain binding site (CD19-2/A) to derive an improved consensus recognition sequence for the Pax-3 C-terminal subdomain. This new consensus differs at six out of eight positions from the C-terminal subdomain recognition motif present in the parent CD19-2/A sequence, and includes a 5'-TT-3' dinucleotide at base pairs 15 and 16 that promotes high affinity binding by both Pax-3 isoforms. However, with a less favorable guanine at position 15, only the Q- isoform retains high affinity binding to this sequence, suggesting that this alternative splicing event might serve to stabilize binding to suboptimal recognition sequences. Finally, mutagenic analysis of the linker demonstrates that both the sequence and the spacing in this region contribute to the enhanced DNA-binding properties of the Pax-3/Q- isoform. Altogether, our studies establish a clear role for the Pax-3 C-terminal subdomain in DNA recognition and, thus, provide insights into an important mechanism by which Pax proteins achieve distinct target specificities.

Amino Acid Substitution↗

Topology mapping of the amino-terminal half of multidrug resistance-associated protein by epitope insertion and immunofluorescence.

The multidrug resistance-associated protein (MRP) is an integral membrane protein that causes multidrug resistance when overexpressed in mammalian cells. Within the ATP-binding cassette superfamily, MRP belongs to a subgroup of structurally and functionally related proteins that includes the yeast cadmium factor 1 and yeast oligomycin resistance I proteins, and the mammalian sulfonylurea receptors SUR1 and SUR2. Hydropathy analysis of these proteins predicts a unique membrane-associated region at the amino terminus followed by a structural unit composed of 12 transmembrane (TM) domains and two nucleotide-binding domains that is characteristic of eukaryotic ATP-binding cassette transporters. The topology of the membrane-associated regions of MRP remains largely unknown and was investigated. Small hemagglutinin epitopes (YPYDVPDYAS) were inserted in predicted hydrophilic segments of the membrane-associated regions from the amino-terminal half of MRP and these proteins were expressed in HeLa cells, and tested for their capacity to confer etoposide resistance. The polarity of the inserted tags with respect to plasma membrane was then deduced by immunofluorescence in intact and permeabilized cells. Insertion of epitopes at positions 4, 163, 271, 574, and 653 produced functional proteins while insertions at positions 127, 417, 461, and 529 abrogated the capacity of MRP to confer drug resistance. Epitopes inserted at positions 4, 163, and 574 were localized extracellularly, whereas those inserted at positions 271 and 653 revealed an intracellular location. Although a single epitope inserted at position 461 was compatible with MRP function, it was inaccessible to the anti-epitope antibody and two copies of the tag at that site abrogated MRP function. These results indicate that the amino terminus of MRP is extracellular, while the linker segment joining the first and second membrane-associated regions is intracellular as is the first nucleotide-binding domain. Our findings are therefore consistent with a topological model of MRP that contains 5 TM segments in the first membrane-associated region and 6 TM segments in the second membrane region.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

Crystal structure of the A3 domain of human von Willebrand factor: implications for collagen binding.

BACKGROUND: Bleeding from a damaged blood vessel is stopped by the formation of a platelet plug. The multimeric plasma glycoprotein, von Willebrand factor (vWF), plays an essential role in this process by anchoring blood platelets to the damaged vessel wall under conditions of high shear stress. This factor mediates platelet adhesion by binding both to collagen of the damaged blood vessel and to glycoprotein Ib on the platelet membrane. The A3 domain of vWF allows it to bind to collagen types I and III present in the perivascular connective tissue of the damaged vessel wall. To gain insight into the mechanism of collagen binding by vWF, we have determined the crystal structure of the human vWF A3 domain. RESULTS: The crystal structure of the 20 kDa A3 domain of human vWF (residues 920-1111), determined by the method of multiwavelength anomalous dispersion at 1.8 A resolution, exhibits a common dinucleotide-binding fold. The putative collagen-binding site of the A3 domain is rather smooth and shows a markedly high concentration of negatively charged residues. This region encompasses a potential metal-binding site containing the motif DXSXS, which is required for ligand interaction in the homologous I-type domains of integrins CR3 and LFA-1. Although vWF A3 has considerable sequence and structural similarity with CR3 and LFA-1 in this region, one loop of A3 adopts a conformation which is incompatible with ion binding. CONCLUSIONS: The structure of the A3 domain suggests that adhesion to collagen is primarily achieved through interactions between negatively charged residues on A3 and positively charged residues on collagen. The absence of a pronounced binding groove precludes a large van der Waals surface interaction between A3 and collagen and is consistent with the low affinity for collagen of a single A3 domain and the requirement for multimeric vWF for tight association with collagen. The absence of bound metal ions upon soaking the crystal in MgCl2 and vWF A3's conformational incompatibility for metal binding is consistent with the absence of a functional role for metal ion binding in A3, which contrasts the metal ion activation required for ligand binding by the homologous integrin I type domains.

Amino Acid Sequence↗

Functional interactions between synthetic alkyl phospholipids and the ABC transporters P-glycoprotein, Ste-6, MRP, and Pgh 1.

The ABC superfamily of transporters includes the mammalian P-glycoprotein family (Class I and Class II P-gps), the multidrug resistance-associated protein (MRP), the Pgh-1 product of Plasmodium falciparum gene pfmdr1, all of which are associated with cellular pleiotropic drug resistance phenomena. STE6, the yeast transporter for the farnesylated peptide pheromone a, is also a member of this family. Structural similarities in this family translate into functional homology as expression of mouse Mdr3S (P-gp), P. falciparum Pgh-1, and human MRP partially restore mating in a sterile yeast mutant lacking a functional STE6 gene. The demonstration that Class II P-gps function as phosphatidylcholine (PC) translocators raise the possibility that other ABC transporters may also interact with physiological lipids. We report the identification of the synthetic lipid and PC analog ET-18-OCH3 (edelfosine) as a substrate for not only Class II P-gp but also for Class I P-gps and surprisingly for the other ABC transporters MRP, Pgh-1, and STE6. Expression of these proteins in the yeast Saccharomyces cerevisiae JPY201 was found to confer cellular resistance to cytotoxic concentrations of this lipid by a factor of 4-20-fold in a growth inhibition assay. The noted activity of ABC transporters toward this synthetic lipid was specific as a mutant variant of Mdr3 (Mdr3F) with reduced activity could not convey cellular resistance to ET-18-OCH3. ET-18-OCH3 was also found capable of blocking a-peptide pheromone transport and STE6 complementation by these ABC proteins. The inhibitory effect of ET-18-OCH3 on cell growth and a-factor transport could be abrogated by incubation with the lipid acceptor protein BSA or by enzymatic cleavage by microsomal alkylglycerol mono-oxygenase (MAMO). MAMO and BSA reversal of the ether lipid effect was only seen in the presence of a functional transporter. These results suggest that the group of cytotoxic synthetic PC analogs studied reveal possible structural and functional aspects common to the ABC transporters tested. Furthermore, the studies with BSA and MAMO suggest that the mechanism of transport of ET-18-OCH3 by these ABC transporters may be related to the flippase mechanism of PC transport by Mdr2.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

The paired-domain regulates DNA binding by the homeodomain within the intact Pax-3 protein.

Pax-3 contains two structurally independent DNA-binding domains, a paired-domain and a homeodomain. Their functional interdependence has been suggested by the analysis of the Sp-delayed (Spd) mouse mutant, in which a glycine to arginine substitution at position 9 of the paired-domain abrogates DNA binding by both domains. This glycine is located in the beta-turn portion of a beta-hairpin motif, and the requirement for this structure was investigated by mutagenesis at this and neighboring positions. At position 9, only substitution with proline increased DNA binding by the paired-domain and homeodomain above the level observed with the Spd arginine mutation, suggesting that the beta-turn is necessary for the function of both DNA-binding domains. Alanine scanning mutagenesis also identified a number of flanking residues important for DNA binding by both domains, emphasizing the requirement of the beta-hairpin for the interaction of Pax-3 with DNA. Furthermore, we show that these mutations reduce binding by the homeodomain at the monomeric level and do not impair dimerization on a TAAT(N)2ATTA consensus motif. In contrast, the wild-type paired-domain was found to prevent dimerization on consensus motifs with 3-base pair spacing of the type TAAT(N)3ATTA. Importantly, both the deleterious effect of the Spd mutation on homeodomain DNA binding and the loss of dimerization on TAAT(N)3ATTA motifs can be transferred to a heterologous homeodomain from the human phox protein. Moreover, the presence of the paired-domain affects sequence discrimination within the 3-base pair spacer in this context. These analyses establish that the beta-hairpin motif is essential for paired-domain and homeodomain DNA binding, and suggest a novel mechanism by which the paired-domain can influence sequence specificity of the homeodomain within the Pax-3 polypeptide.

Amino Acid Sequence↗

Natural resistance to infection with intracellular pathogens: the Nramp1 protein is recruited to the membrane of the phagosome.

The Nramp1 (natural-resistance-associated macrophage protein 1) locus (Bcg, Ity, Lsh) controls the innate resistance or susceptibility of mice to infection with a group of unrelated intracellular parasites which includes Salmonella, Leishmania, and Mycobacterium. Nramp1 is expressed exclusively in professional phagocytes and encodes an integral membrane protein that shares structural characteristics with ion channels and transporters. Its function and mechanism of action remain unknown. The intracellular localization of the Nramp1 protein was analyzed in control 129/sv and mutant Nramp1-/- macrophages by immunofluorescence and confocal microscopy and by biochemical fractionation. In colocalization studies with a specific anti-Nramp1 antiserum and a panel of control antibodies directed against known cellular structures, Nramp1 was found not to be expressed at the plasma membrane but rather localized to the late endocytic compartments (late endosome/lysosome) of resting macrophages in a Lamp1 (lysosomal-associated membrane protein 1)-positive compartment. Double immunofluorescence studies and direct purification of latex bead-containing phagosomes demonstrated that upon phagocytosis, Nramp1 is recruited to the membrane of the phagosome and remains associated with this structure during its maturation to phagolysosome. After phagocytosis, Nramp1 is acquired by the phagosomal membrane with time kinetics similar to Lamp1, but clearly distinct from those of the early endosomal marker Rab5. The targeting of Nramp1 from endocytic vesicles to the phagosomal membrane supports the hypothesis that Nramp1 controls the replication of intracellular parasites by altering the intravacuolar environment of the microbe-containing phagosome.

Animals↗

High-resolution linkage map of mouse chromosome 13 in the vicinity of the host resistance locus Lgn1.

Natural resistance of inbred mouse strains to infection with Legionella pneumophila is controlled by the expression of a single dominant gene on chromosome 13, designated Lgn1. The genetic difference at Lgn1 is phenotypically expressed as the presence or absence of intracellular replication of L. pneumophila in host macrophages. In our effort to identify the Lgn1 gene by positional cloning, we have generated a high-resolution linkage map of the Lgn1 chromosomal region. For this, we have carried out extensive segregation analysis in a total of 1270 (A/J x C57BL/6J) x A/J informative backcross mice segregating the resistance allele of C57BL/6J and the susceptibility allele of A/J. Additional segregation analyses were carried out in three preexisting panels of C57BL/6J x Mus spretus interspecific backcross mice. A total of 39 DNA markers were mapped within an interval of approximately 30 cM overlapping the Lgn1 region. Combined pedigree analyses for the 5.4-cM segment overlapping Lgn1 indicated the locus order and the interlocus distances (in cM): D13Mit128-(1.4)-D13Mit194-(0.1)-D13Mit147-(0.9)-D13 Mit36-(0.9)-D13Mit146-(0.2)-Lgn1/D13Mit37-(1.0)- D13Mit70. Additional genetic linkage studies of markers not informative in the A/J x C57BL/6J cross positioned D13Mit30, -72, -195, and -203, D13Gor4, D13Hun35, and Mtap5 in the immediate vicinity of the Lgn1 locus. The marker density and resolution of this genetic linkage map should allow the construction of a physical map of the region and the isolation of YAC clones overlapping the gene.

Animals↗

High-resolution linkage map in the proximity of the host resistance locus Cmv1.

The mouse chromosome 6 locus Cmv1 controls replication of mouse Cytomegalovirus (MCMV) in the spleen of the infected host. In our effort to clone Cmv1, we have constructed a high-resolution genetic linkage map in the proximity of the gene. For this, a total of 45 DNA markers corresponding to either cloned genes or microsatellites were mapped within a 7.9-cM interval overlapping the Cmv1 region. We have followed the cosegregation of these markers with respect to Cmv1 in a total of 2248 backcross mice from a preexisting interspecific backcross panel of 281 (Mus spretus x C57BL/6J)F1 x C57BL/6J and 2 novel panels of 989 (A/ J x C57BL6)F1 x A/J and 978 (BALB/c x C57BL/6J)F1 x BALB/c segregating Cmv1. Combined pedigree analysis allowed us to determine the following gene order and intergene distances (in cM) on the distal region of mouse chromosome 6: D6Mit216-(1.9)-D6Mit336-(2.2)- D6Mit218-(1.0)-D6Mit52-(0.5)-D6Mit194-(0.2)-Nkrp 1/ D6Mit61/135/257/289/338-(0.4)-Cmv1/Ly49A/D6Mit370++ +- (0.3)-Prp/Kap/D6Mit13/111/219-(0.3)-Tel/D6Mit374/290/ 220/196/195/110-(1.1)-D6Mit25. Therefore, the minimal genetic interval for Cmv1 of 0.7 cM is defined by 13 tightly linked markers including 2 markers, Ly49A and D6Mit370, that did not show recombination with Cmv1 in 1967 meioses analyzed; the proximal limit of the Cmv1 domain was defined by 8 crossovers between Nkrp1/ D6Mit61/135/257/289/338 and Cmv1/Ly49A/D6Mit370, and the distal limit was defined by 5 crossovers between Cmv1/Ly49A/D6Mit370 and Prp/Kap/D6Mit13/111/219. This work demonstrates tight linkage between Cmv1 and genes from the natural killer complex (NKC), such as Nkrp1 and Ly49A, suggesting that Cmv1 may represent an NK cell recognition structure encoded in the NKC region.

3T3 Cells↗

Bactericidal antibody recognition of a PorA epitope of Neisseria meningitidis: crystal structure of a Fab fragment in complex with a fluorescein-conjugated peptide.

Class 1 outer membrane protein PorA of Neisseria meningitidis is a vaccine candidate against bacterial meningitis. Antibodies against PorA are able to induce complement-mediated bacterial killing and thereby play an important role in protection against meningococcal disease. Bactericidal antibodies are all directed against variable regions VR1 and VR2 of the PorA sequence, corresponding to loops 1 and 4 of a two-dimensional topology model of the porin with eight extracellular loops. We have determined the crystal structure to 2.6 A resolution of the Fab fragment of bactericidal antibody MN12H2 against meningococcal PorA in complex with a linear fluorescein-conjugated peptide TKDTNNNL derived from the VR2 sequence of sero-subtype P1.7,16 (residues 180-187) from meningococcal strain H44/76. The peptide folds deeply into the binding cavity of the Fab molecule in a type I beta-turn, with the minimal P1.16 epitope DTNNN virtually completely buried. The structure reveals H-bonds and van der Waals interactions with all minimal epitope residues and one essential salt bridge between Asp-182 of the peptide and His-31 of the MN12H2 light chain. The key components of the recognition of PorA epitope P1.16 by bactericidal antibody MN12H2 correspond well with available thermodynamic data from binding studies. Furthermore, they indicate the structural basis of an increased endemic incidence of infection by group B meningococci in England and Wales since 1981 associated with the occurrence of an Neisseria meningitidis escape mutant (strain-MC58). The observed three-dimensional conformation of the peptide provides a rationale for the development of a synthetic peptide vaccine against meningococcal disease.

Amino Acid Sequence↗

Expression of the human NRAMP1 gene in professional primary phagocytes: studies in blood cells and in HL-60 promyelocytic leukemia.

In the mouse, mutations at the natural resistance-associated macrophage protein 1 (Nramp1) gene abrogate resistance to infection with antigenically unrelated intracellular parasites such as Mycobacterium, Salmonella, and Leishmania. Nramp1 expression is restricted to reticuloendothelial organs and peripheral blood leukocytes, where the protein may function as a membrane transporter of an as yet to be identified substrate. To identify the human blood cell type(s) expressing NRAMP1 mRNA and determine how Nramp1 expression is regulated in these cells, we have examined separated populations of peripheral blood leukocytes and in vitro cell lines. We observed that polymorphonuclear leukocytes (PMN) are the major site of NRAMP1 expression, followed to a lesser degree by monocytes (MN). Migration of MN to tissues (alveolar macrophages) or maturation in vitro (long-term culture) was associated with a higher level of NRAMP1 expression compared with blood MN. Northern analyses of RNA from model cultured cells showed absence of NRAMP1 expression in transformed cell lines from either erythroid or lymphoid T or B lineages as well as progenitors of the monocyte/macrophage pathway (KG1, U937, THP1), and the HL-60 promyelocytic leukemia. Induction of differentiation of HL-60 cells toward either the monocyte/macrophage (vitamin D3, phorbol ester) or the granulocyte pathways (DMF, DMSO), as measured by induction of IL8-Rb, c-FMS, and CD14 marker gene expression, was concomitant with a strong induction of NRAMP1 expression. These results suggest that NRAMP1 expression is specific to the myeloid lineage and is acquired during the maturation of PMN and MN. The possibility that NRAMP1 may be a component of the phagosomal/endosomal apparatus common to PMN and MN is discussed.

Base Sequence↗

Cell-specific and inducible Nramp1 gene expression in mouse macrophages in vitro and in vivo.

Mutations in the Nramp1 gene abolish natural resistance to infections with many unrelated intracellular parasites in vivo. Global cDNA amplification was used to analyse Nramp1 mRNA expression in bone marrow-derived cell colonies corresponding to either undifferentiated progenitors or to mature lymphoid, erythroid, and myeloid lineages. Nramp1 mRNA was detected in mature myeloid colonies expressing molecular markers for either the monocyte/macrophage or granulocytic lineages. Having established constitutive expression of Nramp1 in phagocytic cells, the parameters of inducible Nramp1 expression by cytokines and lipopolysaccharide (LPS) were studied in the mouse macrophage cell line RAW 264.7. LPS caused up-regulation of Nramp1 expression in a time- and dose-dependent fashion. This induction required de novo protein synthesis and was abrogated by treatment with cycloheximide. Treatment with interferon-gamma (IFN-gamma) also caused a modest but reproducible twofold induction of Nramp1 mRNA expression. In addition, maximum Nramp1 mRNA induction in RAW 264.7 cells was observed after pretreatment with IFN-gamma followed by LPS exposure. In vivo, Nramp1 mRNA expression could be up-regulated in macrophage populations by intraperitoneal injection of either LPS or thioglycollate. Together these results indicate that Nramp1 is expressed in professional phagocytes of the myeloid lineage and can be further up-regulated during macrophage activation in response to infectious, inflammatory, or cytokine stimuli. Finally, the patterns of constitutive and inducible expression of Nramp1 have been compared to those of the inducible nitric oxide synthase (iNOS) gene in the same cells.

Animals↗

Cloning and characterization of the OsNramp family from Oryza sativa, a new family of membrane proteins possibly implicated in the transport of metal ions.

The mammalian Nramp1 protein is an integral membrane protein expressed exclusively in macrophages, where it plays a critical role in the ability of these cells to destroy ingested microbes. The bactericidal mechanism of action of Nramp1 remains unknown. We report the identification and characterization of cDNA clones corresponding to three homologues of the mammalian Nramp1 gene from the genome of Oryza sativa, OsNramp1, OsNramp2, and OsNramp3. These three genes encode a novel group of highly similar hydrophobic polypeptides sharing between 64% and 75% sequence similarity, that show similar hydropathy profiles, and predicted secondary structure, including the same number, position, and sequence characteristics (including conserved charges) of transmembrane domains. Together, these define a highly conserved membrane associated hydrophobic core. The three plant proteins show a remarkable degree of sequence similarity with their mammalian counterpart (60% to 70% similarity), including primary and secondary structure elements previously described in ion transporters and channels. Expression studies in normal plant tissues indicate that while OsNramp1 is expressed primarily in roots, and OsNramp2 is primarily expressed in leaves, OsNramp3 is expressed in both tissues. The recent discovery that the yeast Nramp homologue SMF1 functions as a manganese transporter raises the exciting possibility that OsNramp encodes a family of metal ion transporters in plants.

Amino Acid Sequence↗

Reciprocal effect of Waardenburg syndrome mutations on DNA binding by the Pax-3 paired domain and homeodomain.

The Pax-3 protein contains two DNA-binding domains, a paired domain and a homeodomain. Mutations in Pax-3 cause Waardenburg syndrome (WS) in humans and the mouse Splotch (Sp) phenotype. In the Sp-delayed mouse, a mutation in the Pax-3 paired domain (G9R) abrogates the DNA-binding activity of both the paired domain and the homeodomain, suggesting that they may functionally interact. To investigate this possibility further, we have analyzed the DNA-binding properties of additional point mutants in the Pax-3 paired domain and homeodomain that occur in WS patients (F12L, N14H, G15S, P17L, R23L, G48A, S51F and G66D in the paired domain, V47F and R53G in the homeodomain), the Pax-1 un mutation (G15A) and a substitution associated with Peters' anomaly in the PAX-6 gene (R23G). Within the paired domain, seven of 10 mutations were found to abrogate DNA-binding by the paired domain. Remarkably, these seven mutations also affected DNA binding by the homeodomain, causing either a complete loss (P17L and G66D), a reduction (R23G, R23L, G15S and G15A) or an increase in DNA-binding activity (N14H). In addition, the effect of paired domain mutations occurred at the level of monomer formation by the homeodomain, while the dimerization potential of this domain seemed unaffected in mutants where it could be analyzed. Furthermore, while both homeodomain mutations were found to abolish DNA binding by this domain, the R53G mutation also abrogated DNA binding by the paired domain. The important observation that independent mutations in either domain can affect DNA binding by the other in the intact Pax-3 protein strongly suggests that the two domains are not functionally independent but bind DNA through cooperative interactions. Modeling the deleterlous mutations on the three-dimensional structure of the paired domain of Drosophila Prd shows that these mutations cluster at the DNA interface, thus suggesting that a series of DNA contacts are essential for DNA binding by both the paired domain and the homeodomain of Pax-3.

Amino Acid Sequence↗