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PubMed1996

Thermal stability of horse spleen apoferritin and human recombinant H apoferritin.

The thermal stability of horse spleen apoferritin, a heteropolymer composed of 90% L and 10% H chains, has been studied by differential scanning calorimetry and compared with that of the human recombinant H homopolymer. The denaturation temperatures (Tm) are significantly higher for the horse spleen polymer than for the recombinant protein under all experimental conditions (e.g., at pH 7, Tm values are > or = 93 and 77 degrees C, respectively). The thermal denaturation process displays substantial reversibility for both polymers up to a few degrees below Tm, as indicated by CD measurements in the far and near uv regions. At temperatures higher than Tm the thermograms are influenced by the exothermic contribution of aggregation and/or precipitation. The H homopolymer thermogram, which is not distorted by the exotherm, is consistent with a multistate denaturation process. Acid dissociation of apoferritin produces stable dimeric subunits. The thermal unfolding of both dimeric subunits is reversible at least up to Tm and is characterized by an inversion of stability relative to the polymers (at pH 3.5, Tm is 42 degrees C for the horse spleen and 50 degrees C for the H subunit). These results indicate that the stabilization of the polymeric structure arises mainly from interactions between dimers, in accordance with the crystallographic evidence that the dimers are the building blocks of the polymeric molecule.

Animals↗
PubMed1998

High-performance capillary electrophoretic characterization of different types of oligo- and polysialic acid chains.

We have carried out comparative structural analysis of novel oligo- and polysialic acid chains from diverse sources. Controlled acid hydrolysates of (a) colominic acid, alpha2-->8-linked homopolymer of N-acetylneuraminic acid (Neu5Ac), (b) alpha2-->8-linked oligo/polyNeu5Gc chains present in rainbow trout egg polysialoglycoprotein, and (c) alpha2-->8-linked oligomers of deaminoneuraminic acid (KDN) residues of KDN-rich glycoprotein derived from rainbow trout vitelline envelope were analyzed by high-performance capillary electrophoresis (HPCE). The results showed that three different types of alpha2-->8-linked oligosialic acids having same degree of polymerization can be separated by HPCE. A partial hydrolysate of colominic acid with mild acid was shown by CE to form intramolecular esters during the controlled hydrolysis and the subsequent workup procedure. In contrast, lactonization of (-->5-Oglycolyl-Neu5Gcalpha2-->)n, alpha2-->5-Oglycolyl-linked homopolymer of N-glycolylneuraminic acid (Neu5Gc) present in the egg jelly coat of sea urchin, did not take place as readily as in (-->8Neu5Acalpha2-->)n.

Animals↗
PubMed1993

Occurrence of 2-O-methyl-N-(3-deoxy-L-glycero-tetronyl)-D-perosamine (4-amino-4,6-dideoxy-D-manno-pyranose) in lipopolysaccharide from Ogawa but not from Inaba O forms of O1 Vibrio cholerae.

A structural study by GC-MS, methylation analysis, and 1H and 13C NMR was carried out on alpha (1-->2)-linked linear N-(3-deoxy-L-glycero-tetronyl)-D-perosamine homopolymer constituting the O-polysaccharide chain of lipopolysaccharide from O1 Vibrio cholerae Ogawa and Inaba O forms. Occurrence of 2-O-methyl-N-(3-deoxy-L-glycero-tetronyl)-D-perosamine was demonstrated at the non-reducing terminus of the perosamine-homopolymer of lipopolysaccharide from the Ogawa O form in contrast to the presence of N-(3-deoxy-L-glycero-tetronyl)-D-perosamine at the nonreducing terminus for the Inaba O form.

Carbohydrate Conformation↗
PubMed1998

Suppression of cell growth by heavy chain ferritin.

While producing recombinant rat liver H and L chain ferritin homopolymers using the baculovirus expression system, we noticed that rat liver H chain ferritin, but not L chain ferritin, had a suppressive effect on the growth of Spodoptera frugiperda (Sf-21) cells. Suppression was observed immediately after infection with recombinant H chain ferritin baculovirus prepared from lysed infected cells. Immediate suppression was observed when purified with either recombinant H chain apoferritin or various holoferritins (loaded with 1,970 +/- 50 or 2,520 +/- 90 atoms of iron/ferritin) indicating that suppression was not due to sequestration of iron required for cell growth. Suppression by H chain ferritin was also observed upon attempting to express the protein in Escherichia coli. Strategies for expression of recombinant rat liver H and L ferritin homopolymers in both prokaryotic and eukaryotic expression systems were developed.

Animals↗
PubMed1997

Hierarchical Structure of Lattices in Film Formation of Core-Shell Type Polymer Microspheres

By adding polystyrene homopolymer in the solid state, super-lattice structures of poly(4-vinyl pyridine) core-polystyrene shell type polymer microspheres were hierarchically changed from a disordered state to a face-centered cubic via a body-centered cubic. The transition of the lattice structures was investigated from the view point of the excluded volume of the microsphere, which was controlled by a changing of the molecular weights and blend tarios of polystyrene homopolymers.

Journal Article↗
PubMed1997

Novel Poly(vinyl ether) Block Copolymers: Adsorption from Aqueous Solutions on alpha-Fe2O3 (Hematite) and the Mechanism of Colloidal Stabilization

The adsorption of diblock copolymers containing different block length ratios of polyvinylmethyl ether (PVME) and poly (vinyloxy-4-butyric acid) (PVOBA) from aqueous solutions onto alpha-Fe2O3 (hematite) was compared with the adsorption of the PVOBA and PVME homopolymers. The effects on the colloidal stabilization in relation to the chemical composition of the polymers were evaluated. The pH was between 7.5 and 9 in all experiments. The PVME homopolymer hardly adsorbs on alpha-Fe2O3, while an adsorbed amount of 0.31 mg/m2 was found for PVOBA, which behaves as a polyelectrolyte at the pH values used. The adsorbed amount of the block copolymers increases with increasing PVME chain length up to 0.95 mg/m2. The high affinity character in the adsorption isotherm is lost above a certain length of the PVME chain in the block copolymer. The adsorbed layer thickness increases with the PVME chain length, while at the same time the chain density on the surface decreases. Adsorption of PVOBA causes a high absolute value of the zeta potential (|zeta|) of the alpha-Fe2O3 particles. The value of |zeta| drops with an increasing length of the PVME chain. The stability of alpha-Fe2O3 dispersions stabilized with block copolymers with a short PVME chain is mainly due to electrical double-layer repulsion. Full steric stabilization is obtained with sufficiently long PVME chains in the block copolymer, making these dispersions insensitive to the salt concentration.

Journal Article↗
PubMed2000

Adsorption of Diblock Copolymers of Poly(ethylene oxide) and Poly(lactide) at Hydrophilic Silica from Aqueous Solution.

The adsorption of a series of amphiphilic poly(ethylene oxide)-poly(DL-lactide) (PEO-PL) diblock copolymers at the water/silica interface was investigated by ellipsometry and reflectometry. For all copolymers, a much higher saturation adsorption is found compared to that of the PEO homopolymers, indicating the importance of the PL block for the adsorption. The copolymers display a saturation adsorption that increases with increasing hydrophobic content of the polymer, and decreases with increasing hydrophilic content of the polymer. Despite this, however, the layer thickness observed is rather similar for all polymers, regardless of the length and composition of the copolymers. Moreover, the layer thicknesses were significantly higher than what would be expected for the unperturbered copolymer dimensions. The initial adsorption kinetics of the different copolymers are comparable. The initial adsorption rate increases cooperatively with concentration and is slower than that expected for diffusion-controlled adsorption. Moreover, the adsorption increases only slightly over a concentration the range from 20 to 50 degrees C. Furthermore, pH titrations show that all polymers exhibit a critical desorption pH of 8-9, which is lower than the corresponding value of pH 10.5 observed for the PEO homopolymer. These results are discussed in terms of the adsorption mechanism and the adsorbed layer structure and formation. Copyright 2000 Academic Press.

Journal Article↗
PubMed1994

Kinetic parameters of the translocation of bacteriophage T4 gene 41 protein helicase on single-stranded DNA.

The bacteriophage T4 gene 41 helicase protein (gp41) carries a single-stranded DNA-dependent ATPase activity that is essential to its helicase activity. This ATPase activity can be stimulated by a wide variety of single-stranded DNA cofactors, including homo-oligomers and homopolymers 8 to approximately 10,000 nucleotide residues in length, and by natural single-stranded DNA, such as bacteriophage M13 DNA. The steady-state ATPase activity of gp41 on single-stranded homopolymeric cofactors is dependent on the length of the cofactor, in that the kinetic parameters Vmax and K(act) (or KmDNA) have a characteristic length dependence. Vmax values for different DNA lengths show a hyperbolic dependence on DNA length, while K(act) values are independent of DNA lengths exceeding approximately 20 nucleotide residues. Use of the detailed theoretical analysis developed in the preceding paper reveals that: (1) these results support the earlier proposal that gp41 translocates on single-stranded DNA in an ATP-dependent manner; (2) translocation is undirectional; (3) translocation is processive to an extent that depends on the base composition of the DNA employed, with the average distance translocated per binding event ranging from 60 to 700 nucleotide residues; and (4) the detailed translocation mechanism of gp41 includes an obligatory slow step before or after the ATP-driven translocation process. Defined lengths of natural and homopolymer single-stranded DNA have also been created as gaps of known length distribution between clusters of gene 32 protein (gp32) bound along long single-stranded DNA molecules. ATPase data obtained with cofactors of this type also show unidirectional ATP-driven translocation of gp41 on both natural and homopolymeric single-stranded DNA. Direct binding studies of gp41 to short dT oligomers reveal two further features of the interaction of gp41 to single-stranded DNA: (1) nucleoside triphosphate binding is necessary for the formation of stable gp41-ssDNA complexes; and (2) the DNA binding site size of gp41 is between 12 and 20 nucleotide residues per protein monomer. Possible translocation mechanisms for gp41 are discussed within the context of these results.

Adenosine Triphosphatases↗
PubMed2000

Two-state expansion and collapse of a polypeptide.

The initial phase of folding for many proteins is presumed to be the collapse of the polypeptide chain from expanded to compact, but still denatured, conformations. Theory and simulations suggest that this collapse may be a two-state transition, characterized by barrier-crossing kinetics, while the collapse of homopolymers and random heteropolymers is continuous and multi-phasic. A new rapid-mixing flow technique has been used to resolve the late stages of polypeptide collapse, at time scales >/=45 microseconds. We have used a laser temperature-jump with fluorescence spectroscopy to resolve the complete time-course of the collapse of denatured cytochrome c with nanosecond time resolution. We find the process to be exponential in time and thermally activated, with an apparent activation energy approximately 9 k(B)T (after correction for solvent viscosity). These results indicate that polypeptide collapse is kinetically a two-state transition. Because of the observed free energy barrier, the time scale of polypeptide collapse is dramatically slower than is predicted by Langevin models for homopolymer collapse.

Animals↗
PubMed2000

Two-state expansion and collapse of a polypeptide.

The initial phase of folding for many proteins is presumed to be the collapse of the polypeptide chain from expanded to compact, but still denatured, conformations. Theory and simulations suggest that this collapse may be a two-state transition, characterized by barrier-crossing kinetics, while the collapse of homopolymers is continuous and multi-phasic. We have used a laser temperature-jump with fluorescence spectroscopy to measure the complete time-course of the collapse of denatured cytochrome c with nanosecond time resolution. We find the process to be exponential in time and thermally activated, with an apparent activation energy approximately 9 k(B)T (after correction for solvent viscosity). These results indicate that polypeptide collapse is kinetically a two-state transition. Because of the observed free energy barrier, the time scale of polypeptide collapse is dramatically slower than is predicted by Langevin models for homopolymer collapse.

Animals↗
PubMed1994

Sequence analysis and expression of the murine cytomegalovirus phosphoprotein pp50, a homolog of the human cytomegalovirus UL44 gene product.

The coding sequence for the murine cytomegalovirus (MCMV) nonstructural phosphoprotein pp50 has previously been mapped to the EcoRI-L fragment of the viral genome. Nucleotide sequencing of both genomic DNA and cDNA clones revealed an open reading frame of 411 amino acids that is homologous to both the human cytomegalovirus (HCMV) UL44 (ICP36) and the human herpesvirus type 6 (HHV-6) p41 open reading frames. Four of the five conserved cysteine residues are located within the highly conserved N-termini of the three proteins. Similar to the HCMV and HHV-6 proteins, pp50 is predicted to have a hydrophilic C-terminus which contains a putative nuclear targeting sequence. Immunofluorescence experiments with monoclonal antibodies specific for pp50 demonstrated that recombinant pp50 expressed transiently in COS-1 cells or during infection by recombinant Vaccinia virus was localized to the nucleus. Similarly, during MCMV infection of Balb/3T3 fibroblasts, pp50 was present in the nuclei of infected cells between 8 and 24 hr postinfection, suggesting that the protein contains a functional nuclear targeting sequence. In addition, we have demonstrated that pp50 is a DNA-binding protein with affinities for both single-stranded and double-stranded DNA. Finally, results from our analysis by nonreducing and native gel electrophoresis, as well as fractionation by sucrose gradients suggested that pp50 expressed in the absence of viral infection can form disulfide-linked homopolymers. Such homopolymers were also present in MCMV-infected cells.

Amino Acid Sequence↗
PubMed1989

Inhibition of human immunodeficiency virus reverse transcriptase by 2',3'-dideoxynucleoside triphosphates: template dependence, and combination with phosphonoformate.

The 2',3'-dideoxynucleoside triphosphates (ddNTPs) are potent substrate analog inhibitors of human immunodeficiency virus (HIV) reverse transcriptase and have clinical utility in the treatment of acquired immunodeficiency syndrome. Several issues regarding the interaction of these compounds with HIV reverse transcriptase were examined. The potency of unsubstituted ddNTPs and the 3'-azido analog of dTTP (AZTTP) was influenced by the choice of template. Both compounds were more potent with the complementary homopolymer templates than with gapped duplex DNA, although the Km for the competing dNTP was similar with different templates. The Ki for AZTTP was greater than for the unsubstituted ddNTPs with either a homopolymer or a gapped duplex DNA template. HIV reverse transcriptase incorporated ddCMP and AZTMP into primed phage m13 DNA at sites specified for insertion of dCMP and dTMP, respectively. ddCTP was more efficiently utilized as a substrate than was AZTTP. Primer elongation due to base misincorporation was observed in the absence of one dNTP. The combined effect of ddNTPs and the pyrophosphate analog phosphonoformate (PFA) on HIV reverse transcriptase was also examined, and inhibition by PFA in combination with ddTTP or AZTTP was mutually exclusive.

Acquired Immunodeficiency Syndrome↗
PubMed1986

Purification and properties of dipeptidase from Escherichia coli AJ005.

A Co2+-dependent dipeptidase from E. coli strain AJ005, a peptidase-deficient mutant, was purified with streptomycin sulfate, ammonium sulfate and DEAE-cellulose. The purified dipeptidase increased by about 106-fold in specific activity, with dilysine as a substrate. The dipeptidase cleaved dilysine to two lysines among the lysine homopolymers, the possibility remaining that it is active toward peptides other than dilysine, since it was investigated in the present study only for activity toward lysine homopolymers. Activity was inhibited 54% by 10(-3) M KCN and completely by 10(-3) M PCMB, EDTA and benzethonium chloride, but not at all by soybean trypsin inhibitors. 78% and 95% of its activity was lost with 30 minutes' treatment at 45 degrees C and 50 degrees C, respectively. The apparent Km value was 6.7 X 10(-4) M for dilysine. It is probable that the dipeptidase differs from dipeptidase DP.

Dipeptidases↗
PubMed1989

Chemical crosslinking of proteins of the influenza virion. 1. Interrelationships.

Purified influenza virus (A/FPV/Rostock/34; H7N1) was reacted with one of three chemical crosslinking reagents [dimethylsuberimidate (DMS), tartryl diazide (TDA) and formaldehyde] under conditions designed to give a ladder of crosslinked polypeptides (putative homo- and heteropolymers) when analysed by SDS-polyacrylamide gel electrophoresis under reducing conditions. The different virion polypeptides were identified by Western blotting with monospecific antisera against HA1, HA2, NP, and M1. When reacted with any crosslinker NP preferentially formed 2mer and 4mer homopolymers while M1 formed 2mers, 4mers, 6mers, and 8mers. 2mers and 3mers of HA1 were detected after crosslinking with TDA and DMS but homopolymers of HA2 could not be identified with certainty due to comigrating M1. One heteropolymer was clearly identified as 1NP:1M1 (with DMS and TDA) and others, as expected, as components of the haemagglutinin spike 1HA1:1HA2, 2HA1:2HA2, and 3HA1:3HA2. Formaldehyde gave rise only to HA1:HA2 polymers. The presence of other heteropolymers containing NP in conjunction with HA2 and HA1 seemed likely. Whenever HA2 ran with an Mr of about 50k it comigrated with M1 suggesting it may have formed (with DMS or TDA) a 1HA2:1M1 heterodimer. However it is possible that this band consisted of HA2 homodimers comigrating with M1 homodimers. Patterns of crosslinking with DMS and TDA were similar although not identical, but those obtained with formaldehyde were markedly different. All patterns were highly reproducible.

Antibodies, Viral↗
PubMed1991

Interspecific comparison of the unusually repetitive Drosophila locus mastermind.

The mastermind gene of Drosophila melanogaster encodes a novel, highly repetitive nuclear protein required for neural development. To identify functionally important regions we have initiated an interspecific comparison of the gene in Drosophila virilis. Mastermind transcription and genomic organization are similar in both species and sequence analysis reveals significant conservation in a major cluster of charged amino acids. In contrast, extensive variation is noted in homopolymer domains that immediately flank the acidic cluster. Distinct patterns of evolutionary change can be identified: the major difference between unique regions are occasional amino acid substitutions whereas the repetitive areas are characterized by numerous large in-frame insertions/deletions and a nearly threefold higher rate of amino acid replacement. Conservation of the acidic domain suggests that it has an important functional role whereas the hypervariable homopolymer regions appear to be under less selective constraints than adjacent unique areas.

Amino Acid Sequence↗
PubMed2004

Structure and function of coagulogen, a clottable protein in horseshoe crabs.

Mammalian blood coagulation is based on the proteolytically induced polymerization of fibrinogens. Initially, fibrin monomers noncovalently interact with each other. The resulting homopolymers are further stabilized when the plasma transglutaminase (TGase) intermolecularly cross-links epsilon-(gamma-glutamyl)lysine bonds. In crustaceans, hemolymph coagulation depends on the TGase-mediated cross-linking of specific plasma-clotting proteins, but without the proteolytic cascade. In horseshoe crabs, the proteolytic coagulation cascade triggered by lipopolysaccharides and beta-1,3-glucans leads to the conversion of coagulogen into coagulin, resulting in noncovalent coagulin homopolymers through head-to-tail interaction. Horseshoe crab TGase, however, does not cross-link coagulins intermolecularly. Recently, we found that coagulins are cross-linked on hemocyte cell surface proteins called proxins. This indicates that a cross-linking reaction at the final stage of hemolymph coagulation is an important innate immune system of horseshoe crabs.

Animals↗
PubMed2004

Degradation of acrylic copolymers by white-rot fungi.

Various water-soluble homopolymers and copolymers of acrylamide (AAm) and acrylic acid (AA) which contained phenolic sites, such as guaiacol, lignin sulfonate (LS) and 3,4-dihydroxybenzoic acid (3,4-DHBA), were tested with regard to their degradability by white-rot fungi. Compared with Phanerochaete chrysosporium, Pleurotus ostreatus caused a significantly higher decrease in the average molecular weight ( Mw) of most of the copolymers and the homopolymer under the applied culture conditions. However, the Mw of poly(guaiacol/AAm) increased significantly during incubation with Pl ostreatus. P. chrysosporium was able to reduce only the Mw of the poly(LS/AA) to a significant degree and not that of the other polymers. The mineralization rate of AAm and AA copolymers and terpolymers of AAm, AA and phenolics (LS, 3,4-DHBA, guiacol), which were tested with P. ostreatus and Trametes versicolor, turned out to be low (0.8-3.2%). While the rates of mineralization were similar among all polymers, the decrease in radioactivity from the culture media was higher with the terpolymers bearing phenolic sites. UV spectra of the culture media revealed that the phenolic sites in the terpolymers were significantly degraded by both fungi. Obviously, the degradation of phenolics within the polymer chain caused a higher decrease in Mw but did not significantly increase the mineralization rate.

Acrylamides↗
PubMed2006

Production of polyhydroxyalkanoates from methanol by a new methylotrophic bacterium Methylobacterium sp. GW2.

A new bacterial strain, isolated from groundwater contaminated with explosives, was characterized as a pink-pigmented facultative methylotroph, affiliated to the genus Methylobacterium. The bacterial isolate designated as strain GW2 was found capable of producing the homopolymer poly-3-hydroxybutyrate (PHB) from various carbon sources such as methanol, ethanol, and succinate. Methanol acted as the best substrate for the production of PHB reaching 40 % w/w dry biomass. PHB accumulation was observed to be a growth-associated process, so that there was no need for two-step fermentation. Optimal growth occurred at 0.5 % (v/v) methanol concentration, and growth was strongly inhibited at alpha concentration above 2 % (v/v). Methylobacterium sp. strain GW2 was also able to accumulate the copolyester poly-3-hydroxybutyrate-poly-3-hydroxyvalerate (PHB/HV) when valeric acid was supplied as an auxiliary carbon source to methanol. After 66 h, a copolymer content of 30 % (w/w) was achieved with a PHB to PHV ratio of 1:2. Biopolymers produced by strain GW2 had an average molecular weight ranging from 229,350 to 233,050 Da for homopolymer PHB and from 362,430 to 411,300 Da for the copolymer PHB/HV.

Biopolymers↗