Electrophoresis buffers for polyacrylamide gels at various pH

Inhibition of myelin-cleaving poteolytic activities by interferon-beta in rat astrocyte cultures. Comparative analysis between gelatinases and calpain-II

Background

Proteolytic enzymes have been implicated in the pathogenesis of Multiple Sclerosis (MS) for both their ability to degrade myelin proteins and for their presence in MS plaques.In this study we investigated whether interferon-beta (IFN-β) could differently modulate the activity and the expression of proteolytic activities against myelin basic protein (MBP) present in lipopolysaccharide (LPS)-activated astrocytes.

Methodology/Principal Findings

Rat astrocyte cultures were activated with LPS and simultaneously treated with different doses of IFN-β. To assess the presence of MBP-cleaving proteolytic activity, culture supernatants and cellular extracts collected from astrocytes were incubated with exogenous MBP. A MBP-degrading activity was found in both lysates and supernatants from LPS-activated astrocytes and was dose-dependently inhibited by IFN-β. The use of protease inhibitors as well as the zymographic analysis indicated the presence of calpain II (CANP-2) in cell lysates and gelatinases A (MMP-2) and B (MMP-9) in cell supernatants. RT-PCR revealed that the expression of CANP-2 as well as of MMP-2 and MMP-9 was increased in LPS-activated astrocytes and was dose-dependently inhibited by IFN-β treatment. The expression of calpastatin, the natural inhibitor of CANPs, was not affected by IFN-β treatment. By contrast, decreased expression of TIMP-1 and TIMP-2, the natural inhibitors of MMP-9 and MMP-2, respectively, was observed in IFN-β-treated astrocytes compared to LPS-treated cells. The ratio enzyme/inhibitor indicated that the effect of IFN-β treatment is more relevant to CANP-2 than on MMPs.

Conclusions/ Significance

These results suggest that the neuroinflammatory damage during MS involves altered balance between multiple proteases and their inhibitors and indicate that IFN-β is effective in regulating different enzymatic systems involved in MS pathogenesis.

Glycolate oxidase isozymes are coordinately controlled by GLO1 and GLO4 in rice

Glycolate oxidase (GLO) is a key enzyme in photorespiratory metabolism. Four putative GLO genes were identified in the rice genome, but how each gene member contributes to GLO activities, particularly to its isozyme profile, is not well understood. In this study, we analyzed how each gene plays a role in isozyme formation and enzymatic activities in both yeast cells and rice tissues. Five GLO isozymes were detected in rice leaves. GLO1 and GLO4 are predominately expressed in rice leaves, while GLO3 and GLO5 are mainly expressed in the root. Enzymatic assays showed that all yeast-expressed GLO members except GLO5 have enzymatic activities. Further analyses suggested that GLO1, GLO3 and GLO4 interacted with each other, but no interactions were observed for GLO5. GLO1/GLO4 co-expressed in yeast exhibited the same isozyme pattern as that from rice leaves. When either GLO1 or GLO4 was silenced, expressions of both genes were simultaneously suppressed and most of the GLO activities were lost, and consistent with this observation, little GLO isozyme protein was detected in the silenced plants. In contrast, no observable effect was detected when GLO3 was suppressed. Comparative analyses between the GLO isoforms expressed in yeast and the isozymes from rice leaves indicated that two of the five isozymes are homo-oligomers composed of either GLO1 or GLO4, and the other three are hetero-oligomers composed of both GLO1 and GLO4. Our current data suggest that GLO isozymes are coordinately controlled by GLO1 and GLO4 in rice, and the existence of GLO isozymes and GLO molecular and compositional complexities implicate potential novel roles for GLO in plants.

Resolution-enhanced native acidic gel electrophoresis: a method for resolving, sizing, and quantifying prion protein oligomers

The formation of β-sheet-rich prion protein (PrP(β)) oligomers from native or cellular PrP(c) is thought to be a key step in the development of prion diseases. To assist in this characterization process we have developed a rapid and remarkably high resolution gel electrophoresis technique called RENAGE (resolution-enhanced native acidic gel electrophoresis) for separating, sizing, and quantifying oligomeric PrP(β) complexes. PrP(β) oligomers formed via either urea/salt or acid conversion can be resolved by RENAGE into a clear set of oligomeric bands differing by just one subunit. Calibration of the size of the PrP(β) oligomer bands was made possible with a cross-linked mouse PrP(90-232) ladder (1- to 11-mer) generated using ruthenium bipyridyl-based photoinduced cross-linking of unmodified proteins (PICUP). This PrP PICUP ladder allowed the size and abundance of PrP(β) oligomers formed from urea/salt and acid conversion to be determined. This distribution consists of 7-, 8-, 9-, 10-, and 11-mers, with the most abundant species being the 8-mer. The high-resolution separation afforded by RENAGE has allowed us to investigate distinctive size and population changes in PrP(β) oligomers formed under various conversion conditions, with various construct lengths, from various species or in the presence of anti-prion compounds.

Naturally occurring flavonoids as inhibitors of purified cytosolic glutathione S-transferase

Flavonoids are known to modulate catalytic activity and expression of various enzymes. Glutathione S-transferases (GSTs) are the important biotransformation enzymes defending cells against potentially toxic xenobiotics. Therefore, the modulation of GST activity may influence detoxification of xenobiotics. The aim of this study was to evaluate the in vitro inhibitory activity of several dietary flavonoids towards purified equine liver cytosolic GST. Pure GST was incubated in the presence or absence of flavonoids (10 nM-100 µM), its activity was assayed using 1-chloro-2,4-dinitrobenzene (CDNB) as a substrate, and half maximal inhibitory concentrations (IC(50)) were determined. The obtained results were confirmed by GST activity staining of native polyacrylamide gel electrophoresis (PAGE) gels. For the most potent inhibitor, the inhibition kinetics study was performed. From 24 flavonoids tested, the most potent GST inhibitor was gallocatechin gallate (IC(50) = 1.26 µM). The inhibition kinetics of this compound followed noncompetitive mechanism versus both glutathione (K(i) = 35.9 µM) and CDNB (K(i) = 34.1 µM). The inhibitory potency of different flavonoids for GST activity depended mainly on the pattern of hydroxylation and number of hydroxyl groups in the ring B. Especially, pyrogallol-type catechins with 3-OH group esterified with gallic acid showed strong potential to inhibit GST in vitro.

Analysis of a calcium-binding EF-hand protein family in Fasciola gigantica

Transcriptome data supports the notion of a Platyhelminthes-specific protein family that is characterized by combination of two N-terminal EF-hands and a C-terminal dynein light chain-like domain. Family members in schistosomes induce an IgE response that has been connected with resistance to reinfection in schistosomiasis and is considered as a marker of protection. In the present study, we have compared three homologs of the liver fluke Fasciola gigantica for their immunological properties in mouse. Antisera raised against the recombinant proteins detected the native proteins in tegumental type tissues and epithelial linings of excretory system and intestinal tract. The recombinant EF-hand domains induced strong IgG and IgE responses in immunised mice while only weak to moderate responses were observed against the complete recombinant proteins and their DLC-like domains. Parasite crude worm and tegumental extract antisera reacted predominantly with one isoform and its EF-hand domain. Sera of F. gigantica infected mice did not react with the recombinant proteins. The RNA products of the three genes were detected from the metacercarial up to the adult stage. These observations indicate that the investigated EF-hand proteins are not at the frontier of humoral host/parasite interaction in acute fascioliasis gigantica in mouse but are acting as intracellular proteins in tissues that interface with the parasite's environment or tubular tracts.

Overexpression, purification, crystallization and preliminary crystallographic studies of a hyperthermophilic adenylosuccinate synthetase from Pyrococcus horikoshii OT3

Adenylosuccinate synthetase (AdSS) is a ubiquitous enzyme that catalyzes the first committed step in the conversion of inosine monophosphate (IMP) to adenosine monophosphate (AMP) in the purine-biosynthetic pathway. Although AdSS from the vast majority of organisms is 430-457 amino acids in length, AdSS sequences isolated from thermophilic archaea are 90-120 amino acids shorter. In this study, crystallographic studies of a short AdSS sequence from Pyrococcus horikoshii OT3 (PhAdSS) were performed in order to reveal the unusual structure of AdSS from thermophilic archaea. Crystals of PhAdSS were obtained by the microbatch-under-oil method and X-ray diffraction data were collected to 2.50 Å resolution. The crystal belonged to the trigonal space group P3(2)12, with unit-cell parameters a = b = 57.2, c = 107.9 Å. There was one molecule per asymmetric unit, giving a Matthews coefficient of 2.17 Å(3) Da(-1) and an approximate solvent content of 43%. In contrast, the results of native polyacrylamide gel electrophoresis and analytical ultracentrifugation showed that the recombinant PhAdSS formed a dimer in solution.

Cysteine digestive peptidases function as post-glutamine cleaving enzymes in tenebrionid stored-product pests

The major storage proteins in cereals, prolamins, have an abundance of the amino acids glutamine and proline. Storage pests need specific digestive enzymes to efficiently hydrolyze these storage proteins. Therefore, post-glutamine cleaving peptidases (PGP) were isolated from the midgut of the stored-product pest, Tenebrio molitor (yellow mealworm). Three distinct PGP activities were found in the anterior and posterior midgut using the highly-specific chromogenic peptide substrate N-benzyloxycarbonyl-L-Ala-L-Ala-L-Gln p-nitroanilide. PGP peptidases were characterized according to gel elution times, activity profiles in buffers of different pH, electrophoretic mobility under native conditions, and inhibitor sensitivity. The results indicate that PGP activity is due to cysteine and not serine chymotrypsin-like peptidases from the T. molitor larvae midgut. We propose that the evolutionary conservation of cysteine peptidases in the complement of digestive peptidases of tenebrionid stored-product beetles is due not only to the adaptation of insects to plants rich in serine peptidase inhibitors, but also to accommodate the need to efficiently cleave major dietary proteins rich in glutamine.

N-acetyl-D-galactosamine-specific lectin isolated from the seeds of Carica papaya

N-Acetyl-D-galactosamine (GalNAc)-specific lectins are of great interest because they have been reported to detect tumor-associated antigens of malignant cells. We isolated a novel lectin from Carica papaya seeds, named C. papaya lectin (CPL). Purification of the lectin involved ammonium sulfate fractionation and DEAE anion exchange and repeated gel filtration chromatography. Inhibition of CPL causing hemagglutination on human erythrocytes showed that the lectin shows specificity to GalNAc and lactose. Surface plasmon resonance further revealed that the lectin possesses high specificity toward GalNAc with a dissociation constant of 5.5 × 10(-9) M. The lectin is composed of 38- and 40-kDa subunits with a molecular mass of ∼804 kDa estimated by size-exclusion high-performance liquid chromatography. Incubation of CPL with Jurkat T cells showed significant induction of IL-2 cytokine, which suggests that CPL has potent immunomodulatory effects on immune cells.

Digestive proteolysis organization in two closely related Tenebrionid beetles: red flour beetle (Tribolium castaneum) and confused flour beetle (Tribolium confusum)

The spectra of Tribolium castaneum and T. confusum larval digestive peptidases were characterized with respect to the spatial organization of protein digestion in the midgut. The pH of midgut contents in both species increased from 5.6-6.0 in the anterior to 7.0-7.5 in the posterior midgut. However, the pH optimum of the total proteolytic activity of the gut extract from either insect was pH 4.1. Approximately 80% of the total proteolytic activity was in the anterior and 20% in the posterior midgut of either insect when evaluated in buffers simulating the pH and reducing conditions characteristic for each midgut section. The general peptidase activity of gut extracts from either insect in pH 5.6 buffer was mostly due to cysteine peptidases. In the weakly alkaline conditions of the posterior midgut, the serine peptidase contribution was 31 and 41% in T. castaneum and T. confusum, respectively. A postelectrophoretic peptidase activity assay with gelatin also revealed the important contribution of cysteine peptidases in protein digestion in both Tribolium species. The use of a postelectrophoretic activity assay with p-nitroanilide substrates and specific inhibitors revealed a set of cysteine and serine endopeptidases, 8 and 10 for T. castaneum, and 7 and 9 for T. confusum, respectively. Serine peptidases included trypsin-, chymotrypsin-, and elastase-like enzymes, the latter being for the first time reported in Tenebrionid insects. These data support a complex system of protein digestion in the Tribolium midgut with the fundamental role of cysteine peptidases.

Autocatalytic processing of procathepsin B is triggered by proenzyme activity

Cathepsin B (EC 3.4.22.1) and other cysteine proteases are synthesized as zymogens, which are processed to their mature forms autocatalytically or by other proteases. Autocatalytic processing was suggested to be a bimolecular process, whereas initiation of the processing has not yet been clarified. Procathepsin B was shown by zymography to hydrolyze the synthetic substrate 7-N-benzyloxycarbonyl-L-arginyl-L-arginylamide-4-methylcoumarin (Z-Arg-Arg-NH-MEC), suggesting that procathepsin B is catalytically active. The activity-based probe DCG-04, which is an E-64-type inhibitor, was found to label both mature cathepsin B and its zymogen, confirming the zymography data. Mutation analyses in the linker region between the propeptide and the mature part revealed that autocatalytic processing of procathepsin B is largely unaffected by mutations in this region, including mutations to prolines. On the basis of these results, a model for autocatalytic activation of cysteine cathepsins is proposed, involving propeptide dissociation from the active-site cleft as the first step during zymogen activation. This unimolecular conformational change is followed by a bimolecular proteolytic removal of the propeptide, which can be accomplished in one or more steps. Such activation, which can be also facilitated by glycosaminoglycans or by binding to negatively charged surfaces, may have important physiological consequences because cathepsin zymogens were often found secreted in various pathological states.

Transverse urea-gradient gel electrophoresis

Monitoring the cooperative unfolding transition induced when a protein is exposed to elevated temperature or a chemical denaturant is an important strategy for characterizing the conformational properties of a globular protein. This transition may be analyzed quantitatively by a variety of spectroscopic techniques, but a simpler alternative is described in this unit: urea-gradient gel electrophoresis. The pattern produced in the resulting gel can be used to estimate both the free energy change for unfolding and the rate of the unfolding transition. In addition, the technique can help identify either covalent or conformational heterogeneity in a protein sample. Because urea-gradient gel patterns are sensitive to several parameters, including hydrodynamic volume, net charge, and conformational stability, the technique can be particularly useful for comparing two forms of a protein, e.g., a natural form and the product of recombinant bacteria.

Relevant antibody subsets against MOG recognize conformational epitopes exclusively exposed in solid-phase ELISA

A pathogenic role for circulating anti-myelin antibodies is difficult to establish in multiple sclerosis (MS). Here, we unravel a broad heterogeneity within the anti-myelin oligodendrocyte glycoprotein (MOG) antibodies in humans and non-human primates, and demonstrate that detection of important epitopes of MOG within the pathogenic repertoire is exclusively dependent on presentation on a solid-phase MOG conformer. Results of ELISA and those of a liquid-phase assay were compared using a MOG protein with identical sequence but different conformations. We tested sera from 50 human subjects, plasma of Callithrix jacchus marmosets known to contain antibodies reactive to either conformational or linearized MOG, and monoclonal, conformation-dependent anti-MOG antibodies. We have found no antibody reactivity against the soluble MOG conformer in human serum, and show that this lack of detection is not due to technical artifacts. Rather, dominant epitopes of MOG are not displayed in soluble phase, as shown by a complete lack of binding of conformation-dependent mAb. In MP4-immune marmosets that exhibit demyelinating pathology due to spreading of antibody determinants to myelin-embedded MOG, only ELISA can detect pathogenic circulating anti-MOG antibodies. Thus, the accurate detection of important subsets of pathogenic anti-MOG antibodies requires methods in which MOG is displayed similarly to its natural conformation in myelin.

Probing the stability of native and activated forms of alpha2-macroglobulin

alpha2-Macroglobulin (alpha2M) is a 718 kDa homotetrameric proteinase inhibitor which undergoes a large conformational change upon activation. This conformational change can occur either by proteolytic attack on an approximately 40 amino acid stretch, the bait region, which results in the rupture of the four thioester bonds in alpha2M, or by direct nucleophilic attack on these thioesters by primary amines. Amine activation circumvents both bait region cleavage and protein incorporation, which occurs by proteolytic activation. These different activation methods allow for examination of the roles bait region cleavage and thioester rupture play in alpha2M stability. Differential scanning calorimetry and urea gel electrophoresis demonstrate that both bait region cleavage and covalent incorporation of protein ligands in the thioester pocket play critical roles in the stability of alpha2M complexes.

The two divergent PEP-carboxylase catalytic subunits in the green microalga Chlamydomonas reinhardtii respond reversibly to inorganic-N supply and co-exist in the high-molecular-mass, hetero-oligomeric Class-2 PEPC complex

Our recent molecular studies revealed two divergent PEP-carboxylase (PEPC [Ppc]) encoding genes in the green microalga Chlamydomonas reinhardtii, CrPpc1 and CrPpc2, which are coordinately responsive to changes in inorganic-N and -C supply at the transcript level [Mamedov, T.G., Moellering, E.R. and Chollet, R. (2005) Identification and expression analysis of two inorganic C- and N-responsive genes encoding novel and distinct molecular forms of eukaryotic phosphoenolpyruvate carboxylase in the green microalga C. reinhardtii, Plant J. 42, 832-843]. Here, we report the distribution of these two encoded catalytic subunits in the minor Class-1 and predominant Class-2 PEPC enzyme-forms, the latter of which is a novel high-molecular-mass, hetero-oligomeric complex containing both CrPpc1 (p109) and CrPpc2 (p131) polypeptides. The Class-1 enzyme, however, is a typical PEPC homotetramer comprised solely of p109. We also document that the amount of both CrPpc1/2 catalytic subunits is up-/down-regulated by varying levels of NH(4)(+) supplied to the culture medium.

Differential effects of flavonols on inactivation of α1-antitrypsin induced by hypohalous acids and the myeloperoxidase–hydrogen peroxide–halide system

Alpha1-antitrypsin is well known for its ability to inhibit human neutrophil elastase. Pretreatment of alpha1-antitrypsin with hypohalous acids HOCl and HOBr as well as with the myeloperoxidase-hydrogen peroxide-chloride (or bromide) system inactivated this proteinase. The flavonols rutin, quercetin, myricetin, and kaempferol inhibited the inactivation of alpha1-antitrypsin by HOCl and HOBr with rutin having the most pronounced effect. In contrast, these flavonols did not remove the proteinase inactivation by the myeloperoxidase-hydrogen peroxide-halide system. Taurine did not protect against the inactivation of alpha1-antitrypsin by HOCl, HOBr, or the myeloperoxidase-hydrogen peroxide-halide system, while methionine was efficient in all systems. A close association between myeloperoxidase and alpha1-antitrypsin was revealed by native gel electrophoresis and in-gel peroxidase staining. In addition, alpha1-antitrypsin binds to the myeloperoxidase components transferred after SDS-PAGE on a blotting membrane. With this complex formation, myeloperoxidase overcomes the natural antioxidative protective system of plasma and prevents the inactivation of alpha1-antitrypsin.

Ability of hyaluronidase 2 to degrade extracellular hyaluronan is not required for its function as a receptor for jaagsiekte sheep retrovirus

Jaagsiekte sheep retrovirus (JSRV) uses hyaluronidase 2 (Hyal2) as a cell entry receptor. By making inactivating mutations to the catalytic residues of human Hyal2, we found that hyaluronidase activity was dispensable for its receptor function. The affinities of the JSRV envelope glycoprotein for Hyal2 and the Hyal2 mutant were similar, and hyaluronan did not block either high-affinity interaction or virus infection. While generating the Hyal2 mutant, we discovered that our previous analysis of the hyaluronidase activity of Hyal2 was affected by a contaminating hyaluronan lyase, which we have identified as the occlusion-derived baculovirus E66 protein of the recombinant baculovirus used to produce Hyal2. We now report that purified human Hyal2 is a weak acid-active hyaluronidase.

Diversity of digestive proteinases in Tenebrio molitor (Coleoptera: Tenebrionidae) larvae

The spectrum of Tenebrio molitor larval digestive proteinases was studied in the context of the spatial organization of protein digestion in the midgut. The pH of midgut contents increased from 5.2-5.6 to 7.8-8.2 from the anterior to the posterior. This pH gradient was reflected in the pH optima of the total proteolytic activity, 5.2 in the anterior and 9.0 in the posterior midgut. When measured at the pH and reducing conditions characteristic of each midgut section, 64% of the total proteolytic activity was in the anterior and 36% in the posterior midgut. In the anterior midgut, two-thirds of the total activity was due to cysteine proteinases, whereas the rest was from serine proteinases. In contrast, most (76%) of the proteolytic activity in the posterior midgut was from serine proteinases. Cysteine proteinases from the anterior were represented by a group of anionic fractions with similar electrophoretic mobility. Trypsin-like activity was predominant in the posterior midgut and was due to one cationic and three anionic proteinases. Chymotrypsin-like proteinases also were prominent in the posterior midgut and consisted of one cationic and four anionic proteinases, four with an extended binding site. Latent proteinase activity was detected in each midgut section. These data support a complex system of protein digestion, and the correlation of proteinase activity and pH indicates a physiological mechanism of enzyme regulation in the gut.

Conformational stability of 17 beta-hydroxysteroid dehydrogenase from the fungus Cochliobolus lunatus

The functional activities of proteins are closely related to their molecular structure and understanding their structure-function relationships remains one of the intriguing problems of molecular biology. We investigated structural changes in 17beta-hydroxysteroid dehydrogenase from the fungus Cochliobolus lunatus (17beta-HSDcl) induced by pH, temperature, salt, urea, guanidine hydrochloride, and coenzyme NADPH binding. At 25 degrees C and within the relatively narrow pH range of 7.0-9.0, 17beta-HSDcl exists in its native conformation as a dimer. This native conformation is thermally stable up to 40 degrees C in this pH range. At 25 degrees C and pH 2.0 in the presence of 150-300 mM NaCl, 17beta-HSDcl forms soluble aggregates enriched in alpha-helical and beta-sheet structures. At higher temperatures and NaCl concentrations, these soluble aggregates start to precipitate. The denaturants urea and guanidine hydrochloride unfold 17beta-HSDcl at concentrations of 1.2 and 0.4 M, respectively. Binding of the coenzyme NADPH to 17beta-HSDcl causes local structural changes that do not significantly affect the thermal stability of this protein.

Alpha-fetoprotein antagonizes X-linked inhibitor of apoptosis protein anticaspase activity and disrupts XIAP-caspase interaction

Previous results have shown that the human oncoembryonic protein alpha-fetoprotein (AFP) induces dose-dependent targeting apoptosis in tumor cells, accompanied by cytochrome c release and caspase 3 activation. AFP positively regulates cytochrome c/dATP-mediated apoptosome complex formation in a cell-free system, stimulates release of the active caspases 9 and 3 and displaces cIAP-2 from the apoptosome and from its complex with recombinant caspases 3 and 9 [Semenkova et al. (2003) Eur. J. Biochem. 270, 276-282]. We suggested that AFP might affect the X-linked inhibitor of apoptosis protein (XIAP)-caspase interaction by blocking binding and activating the apoptotic machinery via abrogation of inhibitory signaling. We show here that AFP cancels XIAP-mediated inhibition of endogenous active caspases in cytosolic lysates of tumor cells, as well as XIAP-induced blockage of active recombinant caspase 3 in a reconstituted cell-free system. A direct protein-protein interaction assay showed that AFP physically interacts with XIAP molecule, abolishes XIAP-caspase binding and rescues caspase 3 from inhibition. The data suggest that AFP is directly involved in targeting positive regulation of the apoptotic pathway dysfunction in cancer cells inhibiting the apoptosis protein function inhibitor, leading to triggering of apoptosis machinery.

Fractionation of digestive proteinases from Tenebrio molitor (Coleoptera: Tenebrionidae) larvae and role in protein digestion

Tenebrio molitor larval digestive proteinases were purified and characterized by gel filtration chromatography combined with activity electrophoresis. Cysteine proteinases, consisting of at least six distinct activities, were found in three chromatographic peaks in anterior and posterior midgut chromatographies. The major activity in the anterior midgut, peak cys II, consisted of cysteine proteinases with Mm of 23 kDa. The predominant peak in the posterior, cys I, was represented by 38 kDa proteinases. The activities of all cysteine proteinases were maximal in buffers from pH 5.0 to 7.0, with 80% stability at pH values from 4.0 to 7.0. In the conditions of the last third of the midgut, the activity and stability of cysteine proteinases was sharply decreased. Trypsin-like activity included a minor peak of "heavy" trypsins with Mm 59 kDa, located mainly in the anterior midgut. An in vitro study of the initial stages of digestion of the main dietary protein, oat 12S globulin, by anterior midgut proteinases revealed that hydrolysis occurred through the formation of intermediate high-Mm products, similar to those formed during oat seed germination. Cysteine proteinases from the cys III peak and heavy trypsins were capable of only limited proteolysis of the protein, whereas incubation with cys II proteinases resulted in substantial hydrolysis of the globulin.

2-D native-PAGE/SDS-PAGE visualization of an oligomer's subunits: Application to the analysis of IgG

A 2-D native-PAGE/SDS-PAGE method for detecting the subunit components of protein oligomers at low picomole sensitivity is presented. IgG was electrophoresed in a native acidic polyacrylamide gel in amounts ranging from 51 pmol to 60 fmol. Silver-staining (native fast silver stain, ammoniacal silver stain, permanganate silver stain), Coomassie-staining (R-250, G-250), metal ion-reverse-staining (zinc, copper), and fluorescent chromophore-staining (SYPRO Ruby) methods were used to visualize the IgG oligomers. The protein zones were then excised, separated by SDS-PAGE, and subunits visualized with a permanganate silver stain. The Coomassie R-250/permanganate silver-staining combination detected IgG subunits using 2 pmol of sample. Coomassie G-250 and native fast silver staining in the first-dimensional gel produced detectable subunits in the second-dimensional separation at 3 and 13 pmol, respectively. Staining with silver (ammoniacal, permanganate), copper, zinc, or SYPRO Ruby in the first-dimensional gel did not produce discernible subunits in the second-dimensional gels due to protein streaking or protein immobilization in the native gel. When using a 2-D native-PAGE/SDS-PAGE system, Coomassie staining of the first-dimensional native gel combined with permanganate silver staining of the second-dimensional denaturing gel provides the most sensitive method (2-3 pmol) for visualizing constituent subunits from their oligomeric assemblies.

Modification of amino acid residues in human serum albumin by myeloperoxidase

Myeloperoxidase is released from stimulated polymorphonuclear leukocytes at inflammatory loci. Besides its bactericidal activity, it interacts with human serum albumin that is essential for the endothelial uptake of myeloperoxidase and its contribution in regulation of the blood vessel tonus. Here, we investigated which kinds of modification dominate in the albumin protein by the myeloperoxidase-hydrogen peroxide system at physiological pH. In the presence of chloride, bromide, and nitrite, the myeloperoxidase-hydrogen peroxide system caused an oxidation, bromination, and nitrosylation/nitration of eight amino acid residues of albumin as detected by fragment analysis of tryptic digests with matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry. An oxygen was incorporated into the methionines Met147, Met353, and Met572 as well as into the tryptophan Trp238. In the case of methionine residues, this oxygen was derived from the water phase as shown using 18O-enriched water. Nitrosylation/nitration was observed at the tryptophan Trp238 and the tyrosines Tyr162, Tyr425, and Tyr476 according to the mass shift of 29 Da and 45 Da. The incorporation of one or two bromines was found into the tyrosines Tyr425 and Tyr476. We did not observe any chlorination of albumin fragments. Thus, myeloperoxidase modifies in multiple ways amino acid residues in human serum albumin.

Effect of hsp70 chaperone on the folding and misfolding of polypeptides modeling an elongating protein chain

Virtually nothing is known about the interaction of co-translationally active chaperones with nascent polypeptides and the resulting effects on peptide conformation and folding. We have explored this issue by NMR analysis of apomyoglobin N-terminal fragments of increasing length, taken as models for different stages of protein biosynthesis, in the absence and presence of the substrate binding domain of Escherichia coli Hsp70, DnaK-beta. The incomplete polypeptides misfold and self-associate under refolding conditions. In the presence of DnaK-beta, however, formation of the original self-associated species is completely or partially prevented. Chaperone interaction with incomplete protein chains promotes a globally unfolded dynamic DnaK-beta-bound state, which becomes folding-competent only upon incorporation of the residues corresponding to the C-terminal H helix. The chaperone does not bind the full-length protein at equilibrium. However, its presence strongly disfavors the kinetic accessibility of misfolding side-routes available to the full-length chain. This work supports the role of DnaK as a "holder" for incomplete N-terminal polypeptides. However, as the chain approaches its full-length status, the tendency to intramolecularly bury non-polar surface efficiently outcompetes chaperone binding. Under these conditions, DnaK serves as a "folding enhancer" by supporting folding of a population of otherwise folding-incompetent full-length protein chains.

Amino acid residues associated with cluster N3 in the NuoF subunit of the proton-translocating NADH-quinone oxidoreductase fromEscherichia coli

The NuoF subunit, which harbors NADH-binding site, of Escherichia coli NADH-quinone oxidoreductase (NDH-1) contains five conserved cysteine residues, four of which are predicted to ligate cluster N3. To determine this coordination, we overexpressed and purified the NuoF subunit and NuoF+E subcomplex in E. coli. We detected two distinct EPR spectra, arising from a [4Fe-4S] cluster (g(x,y,z)=1.90, 1.95, and 2.05) in NuoF, and a [2Fe-2S] cluster (g(x,y,z)=1.92, 1.95, and 2.01) in NuoE subunit. These clusters were assigned to clusters N3 and N1a, respectively. Based on the site-directed mutagenesis experiments, we identified that cluster N3 is ligated to the 351Cx2Cx2Cx40C398 motif.

Smooth muscle cell growth in monolayer and aortic organ culture is promoted by a nonheparin binding endothelial cell-derived soluble factor/s

OBJECTIVE

To characterize endothelial derived soluble factor(s) that regulate neointimal formation in porcine aortic organ cultures.

METHODS AND RESULTS

Endothelial cell (EC) conditioned medium, collected in preconfluent EC cultures at 4 days after plating, stimulates vascular smooth muscle cell (SMC) growth in cell culture and in the intima of porcine aortic organ cultures. EC conditioned medium was fractionated consecutively by salt precipitation, ion exchange chromatography and affinity chromatography on a heparin column. Heparin column nonbound fraction (HNBF) contains an endothelial cell-derived soluble factor/s (ECDSF) that promotes neointimal formation by increasing intimal SMC (iSMC) proliferation, as detected by BrdU labeling and inhibiting iSMC apoptosis, as shown by TUNEL. Trypsin digestion of HNBF resulted in loss of mitogenic activity. HNBF show a prominent 70-kDa band in SDS-NuPAGE.

CONCLUSIONS

Endothelial-derived soluble factor(s) has a molecular weight higher than other growth factors, does not have affinity to heparin, is a protein, at least in the active part of the molecule and increases iSMC number due to increased proliferation and suppression of apoptosis leading to neointimal formation.

Glutamate-41 of Vibrio harveyi acyl carrier protein is essential for fatty acid synthase but not acyl-ACP synthetase activity

Bacterial acyl carrier protein (ACP) is a small, acidic, and highly conserved protein that supplies acyl groups for biosynthesis of a variety of lipid products. Recent modelling studies predict that residues primarily in helix II of Escherichia coli ACP (Glu-41, Ala-45) are involved in its interaction with the condensing enzyme FabH of fatty acid synthase. Using recombinant Vibrio harveyi ACP as a template for site-directed mutagenesis, we have shown that an acidic residue at position 41 is essential for V. harveyi fatty acid synthase (but not acyl-ACP synthetase) activity. In contrast, various replacements of Ala-45 were tolerated by both enzymes. None of the mutations introduced dramatic structural changes based on circular dichroism and native gel electrophoresis. These results confirm that Glu-41 of ACP is a critical residue for fatty acid synthase, but not for all enzymes that utilize ACP as a substrate.

Susceptibility to proteolysis of triosephosphate isomerase from two pathogenic parasites: characterization of an enzyme with an intact and a nicked monomer

The susceptibility to subtilisin of homodimeric triosephosphate isomerase from Trypanosoma brucei (TbTIM) and Trypanosoma cruzi (TcTIM) was studied. Their amino sequence and 3D structure are markedly similar. In 36 h of incubation at a molar ratio of 4 TIM per subtilisin, TcTIM underwent extensive hydrolysis, loss of activity, and large structural alterations. Under the same conditions, only about 50% of the monomers of TbTIM were cleaved in two sites. The higher sensitivity of TcTIM to subtilisin is probably due to a higher intrinsic flexibility. We isolated and characterized TbTIM that had been exposed to subtilisin. It exhibited the molecular mass of the dimer, albeit it was formed by one intact and one nicked monomer. Its k(cat) with glyceraldehyde 3-phosphate was half that of native TbTIM, with no change in K(m). The intrinsic fluorescence of nicked TbTIM was red-shifted by 5 nm. The association between subunits was not affected. The TbTIM data suggest that there are structural differences in the two monomers or that alterations of one subunit change the characteristics of the other subunit. In comparison to the action of subtilisin on TIMs from other species, the trypanosomal enzymes appear to be unique.

Purification and characterisation of glutathione S-transferases from the freshwater clam Corbicula fluminea (Müller)

Glutathione S-transferases (GSTs) are involved in the phase II detoxification metabolism. To provide a molecular basis for their use as biomarkers of pollution, cytosolic GSTs from the freshwater clam Corbicula fluminea have been purified by glutathione-Sepharose affinity chromatography, anion-exchange chromatography (AEC) and reversed-phase (RP) HPLC. SDS-PAGE of visceral mass (VM) affinity-purified extracts revealed four subunits with apparent molecular masses (MW) of 30.2, 29.2, 28.5 and 27.2 kDa. Analysis by non-denaturing PAGE revealed three acidic dimeric proteins with apparent MW of 64, 55 and 45 kDa, named GSTc1, GSTc2 and GSTc3, respectively, based on their elution order by AEC. Only GSTc2 and GSTc3 exhibited GST activity towards 1-chloro-2,4-dinitrobenzene. A tissue-specific subunit pattern was obtained by RP-HPLC of affinity-purified extracts from VM and gills (GI): three major peaks were resolved, one of which was common to both tissues. MW of each VM subunit was determined by electrospray ionisation-mass spectrometry: 23602+/-1 Da for the major subunit and 23289+/-1 Da for the minor ones. Immunoblot analysis revealed all subunits from both tissues were related to the Pi-class GSTs. In addition, minor VM subunits were slightly related to the Mu-class ones. The interest of such molecular studies in biomonitoring programs is discussed.

Site-directed mutagenesis of acyl carrier protein (ACP) reveals amino acid residues involved in ACP structure and acyl-ACP synthetase activity

Acyl carrier protein (ACP) interacts with many different enzymes during the synthesis of fatty acids, phospholipids, and other specialized products in bacteria. To examine the structural and functional roles of amino acids previously implicated in interactions between the ACP polypeptide and fatty acids attached to the phosphopantetheine prosthetic group, recombinant Vibrio harveyi ACP and mutant derivatives of conserved residues Phe-50, Ile-54, Ala-59, and Tyr-71 were prepared from glutathione S-transferase fusion proteins. Circular dichroism revealed that, unlike Escherichia coli ACP, V. harveyi-derived ACPs are unfolded at neutral pH in the absence of divalent cations; all except F50A and I54A recovered native conformation upon addition of MgCl(2). Mutant I54A was not processed to the holo form by ACP synthase. Some mutations significantly decreased catalytic efficiency of ACP fatty acylation by V. harveyi acyl-ACP synthetase relative to recombinant ACP, e.g. F50A (4%), I54L (20%), and I54V (31%), whereas others (V12G, Y71A, and A59G) had less effect. By contrast, all myristoylated ACPs examined were effective substrates for the luminescence-specific V. harveyi myristoyl-ACP thioesterase. Conformationally sensitive gel electrophoresis at pH 9 indicated that fatty acid attachment stabilizes mutant ACPs in a chain length-dependent manner, although stabilization was decreased for mutants F50A and A59G. Our results indicate that (i) residues Ile-54 and Phe-50 are important in maintaining native ACP conformation, (ii) residue Ala-59 may be directly involved in stabilization of ACP structure by acyl chain binding, and (iii) acyl-ACP synthetase requires native ACP conformation and involves interaction with fatty acid binding pocket residues, whereas myristoyl-ACP thioesterase is insensitive to acyl donor structure.

Isolation and purification of the IGF-I protein complex from rabbit seminal plasma: Effects on sperm motility and viability

A protein of about 150 kDa affecting sperm kinetic motility and viability was purified from rabbit seminal plasma. The incubation of rabbit sperm with this purified seminal plasma protein caused significant changes in sperm viability and motility. Moreover, the seminal protein showed a noticeable reactivating effect on immotile spermatozoa. A 10-mg amount of purified protein, added to immotile rabbit spermatozoa suspended in Tris-citrate, pH 7.4, resulted in a 48% reactivation. It is known that circulating insulin-like growth factors are bound to specific high-affinity binding proteins and form complexes with relative molecular masses of about 150 kDa. Western blotting analyses proved the existence of insulin-like growth factor in the protein purified from rabbit seminal plasma and immunofluorescence staining showed the existence of IGF-1 receptor in rabbit spermatozoa. Therefore, we suggest that the purified rabbit seminal plasma protein may represent the protein complex delivering IGF to the sperm cells thus affecting their physiological functions.

beta-Alanine betaine synthesis in the Plumbaginaceae. Purification and characterization of a trifunctional, S-adenosyl-L-methionine-dependent N-methyltransferase from Limonium latifolium leaves

beta-Alanine (beta-Ala) betaine is an osmoprotective compound accumulated by most members of the highly stress-tolerant family Plumbaginaceae. Its potential role in plant tolerance to salinity and hypoxia makes its synthetic pathway an interesting target for metabolic engineering. In the Plumbaginaceae, beta-Ala betaine is synthesized by S-adenosyl-L-methionine-dependent N-methylation of beta-Ala via N-methyl beta-Ala and N,N-dimethyl beta-Ala. It was not known how many N-methyltransferases (NMTases) participate in the three N-methylations of beta-Ala. An NMTase was purified about 1,890-fold, from Limonium latifolium leaves, using a protocol consisting of polyethylene glycol precipitation, heat treatment, anion-exchange chromatography, gel filtration, native polyacrylamide gel electrophoresis, and two substrate affinity chromatography steps. The purified NMTase was trifunctional, methylating beta-Ala, N-methyl beta-Ala, and N,N-dimethyl beta-Ala. Gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analyses indicated that the native NMTase is a dimer of 43-kD subunits. The NMTase had an apparent K(m) of 45 microM S-adenosyl-l-methionine and substrate inhibition was observed above 200 microM. The apparent K(m) values for the methyl acceptor substrates were 5.3, 5.7, and 5.9 mM for beta-Ala, N-methyl beta-Ala, and N,N-dimethyl beta-Ala, respectively. The NMTase had an isoelectric point of 5.15 and was reversibly inhibited by the thiol reagent p-hydroxymercuribenzoic acid.

The effect of net charge on the solubility, activity, and stability of ribonuclease Sa

The net charge and isoelectric pH (pI) of a protein depend on the content of ionizable groups and their pK values. Ribonuclease Sa (RNase Sa) is an acidic protein with a pI = 3.5 that contains no Lys residues. By replacing Asp and Glu residues on the surface of RNase Sa with Lys residues, we have created a 3K variant (D1K, D17K, E41K) with a pI = 6.4 and a 5K variant (3K + D25K, E74K) with a pI = 10.2. We show that pI values estimated using pK values based on model compound data can be in error by >1 pH unit, and suggest how the estimation can be improved. For RNase Sa and the 3K and 5K variants, the solubility, activity, and stability have been measured as a function of pH. We find that the pH of minimum solubility varies with the pI of the protein, but that the pH of maximum activity and the pH of maximum stability do not.

Expression and partial characterization of an elastase from Chromobacterium violaceum

Chromobacterium violaceum was recovered at necropsy from the lungs, liver, spleen, and an interscapular abscess of a Chinese red panda (strain 98-9187) [J. Vet. Diagn. Invest. 12 (2000) 177]. As the lungs exhibited extensive, necrotizing lesions harboring bacterial aggregates, we sought to determine whether C. violaceum produced an elastase that might in part account for these lesions. The C. violaceum type strain (ATCC 12472(T)) and strain 98-9187 were shown to exhibit elastolytic activity by elastin Congo red and elastin nutrient agar assays. The activity was isolated from the periplasmic fraction and was present throughout the growth cycle. Activity increased markedly in late logarithmic phase growth. In elastin-limiting medium, activity rapidly decreased in early stationary phase indicating a tight regulation of yield. The activity was optimal at neutral pH and was sensitive to the metalloproteinase inhibitors EDTA and 1,10-phenanthroline. Activity was restored upon addition of zinc indicating the enzyme is a zinc metalloproteinase. A band corresponding to purified elastase activity was present at approximately 30kDa in a denaturing polyacrylamide gel.

A novel type of carbohydrate-protein linkage region in the tyrosine-bound S-layer glycan of Thermoanaerobacterium thermosaccharolyticum D120-70

The surface-layer (S-layer) protein of Thermoanaerobacterium thermosaccharolyticum D120-70 contains glycosidically linked glycan chains with the repeating unit structure -->4)[alpha-D-Galp-(1-->2)]-alpha-L-Rhap-(1-->3)[beta-D-Glcp-(1--> 6)] -beta-D-Manp-(1-->4)-alpha-L-Rhap-(1-->3)-alpha-D-Glcp-(1--> . After proteolytic degradation of the S-layer glycoprotein, three glycopeptide pools were isolated, which were analyzed for their carbohydrate and amino-acid compositions. In all three pools, tyrosine was identified as the amino-acid constituent, and the carbohydrate compositions corresponded to the above structure. Native polysaccharide PAGE showed the specific heterogeneity of each pool. For examination of the carbohydrate-protein linkage region, the S-layer glycan chain was partially hydrolyzed with trifluoroacetic acid. 1D and 2D NMR spectroscopy, including a novel diffusion-edited difference experiment, showed the O-glycosidic linkage region beta-D-glucopyranose-->O-tyrosine. No evidence was found of additional sugars originating from a putative core region between the glycan repeating units and the S-layer polypeptide. For the determination of chain-length variability in the S-layer glycan, the different glycopeptide pools were investigated by matrix-assisted laser desorption ionization-time of flight mass spectrometry, revealing that the degree of polymerization of the S-layer glycan repeats varied between three and 10. All masses were assigned to multiples of the repeating units plus the peptide portion. This result implies that no core structure is present and thus supports the data from the NMR spectroscopy analyses. This is the first observation of a bacterial S-layer glycan without a core region connecting the carbohydrate moiety with the polypeptide portion.

Expression of human topoisomerase I with a partial deletion of the linker region yields monomeric and dimeric enzymes that respond differently to camptothecin

Human topoisomerase I is a 765-residue protein composed of four major domains as follows: the unconserved and highly charged NH(2)-terminal domain, a conserved core domain, the positively charged linker region, and the highly conserved COOH-terminal domain containing the active site tyrosine. Previous studies of the domain structure revealed that near full topoisomerase I activity can be reconstituted in vitro by fragment complementation between recombinant polypeptides approximating the core and COOH-terminal domains. Here we demonstrate that deletion of linker residues Asp(660) to Lys(688) yields an active enzyme (topo70DeltaL) that purifies as both a monomer and a dimer. The dimer is shown to result from domain swapping involving the COOH-terminal and core domains of the two subunits. The monomeric form is insensitive to the anti-tumor agent camptothecin and distributive during in vitro plasmid relaxation assays, whereas the dimeric form is camptothecin-sensitive and processive. However, the addition of camptothecin to enzyme/DNA mixtures causes enhancement of SDS-induced breakage by both monomeric and dimeric forms of the mutant enzyme. The similarity of the dimeric form to the wild type enzyme suggests that some structural feature of the dimer is providing a surrogate linker. Yeast cells expressing topo70DeltaL were found to be insensitive to camptothecin.

Kinetic properties of the glucose-6-phosphate and 6-phosphogluconate dehydrogenases from Corynebacterium glutamicum and their application for predicting pentose phosphate pathway flux in vivo

The glucose-6-phosphate (Glc6P) and 6-phosphogluconate (6PG) dehydrogenases of the amino-acid-producing bacterium Corynebacterium glutamicum were purified to homogeneity and kinetically characterized. The Glc6P dehydrogenase was a heteromultimeric complex, which consists of Zwf and OpcA subunits. The product inhibition pattern of the Glc6P dehydrogenase was consistent with an ordered bi-bi mechanism. The 6PG dehydrogenase was found to operate according to a Theorell-Chance ordered bi-ter mechanism. Both enzymes were inhibited by NADPH and the 6PG dehydrogenase additionally by ATP, fructose 1,6-bisphosphate (Fru1,6P2), D-glyceraldehyde 3-phosphate (Gra3P), erythrose 4-phosphate and ribulose 5-phosphate (Rib5P). The inhibition by NADPH was considered to be most important, with inhibition constants of around 25 microM for both enzymes. Intracellular metabolite concentrations were determined in two isogenic strains of C. glutamicum with plasmid-encoded NAD- and NADP-dependent glutamate dehydrogenases. NADP+ and NADPH levels were between 130 microM and 290 microM, which is very much higher than the respective Km and Ki values. The Glc6P concentration was around 500 microM in both strains. The in vivo fluxes through the oxidative part of the pentose phosphate pathway calculated on the basis of intracellular metabolite concentrations and the kinetic constants of the purified enzymes determined in vitro were in agreement with the same fluxes determined by NMR after 13C-labelling. From the derived kinetic model thus validated, it is concluded that the oxidative pentose phosphate pathway in C. glutamicum is mainly regulated by the ratio of NADPH and NADP+ concentrations and the specific enzyme activities of both dehydrogenases.

Functionality of purified sigma(N) (sigma(54)) and a NifA-like protein from the hyperthermophile Aquifex aeolicus

The genome sequence of the extremely thermophilic bacterium Aquifex aeolicus encodes alternative sigma factor sigma(N) (sigma(54), RpoN) and five potential sigma(N)-dependent transcriptional activators. Although A. aeolicus possesses no recognizable nitrogenase genes, two of the activators have a high degree of sequence similarity to NifA proteins from nitrogen-fixing proteobacteria. We identified five putative sigma(N)-dependent promoters upstream of operons implicated in functions including sulfur respiration, nitrogen assimilation, nitrate reductase, and nitrite reductase activity. We cloned, overexpressed (in Escherichia coli), and purified A. aeolicus sigma(N) and the NifA homologue, AQ_218. Purified A. aeolicus sigma(N) bound to E. coli core RNA polymerase and bound specifically to a DNA fragment containing E. coli promoter glnHp2 and to several A. aeolicus DNA fragments containing putative sigma(N)-dependent promoters. When combined with E. coli core RNA polymerase, A. aeolicus sigma(N) supported A. aeolicus NifA-dependent transcription from the glnHp2 promoter. The E. coli activator PspFDeltaHTH did not stimulate transcription. The NifA homologue, AQ_218, bound specifically to a DNA sequence centered about 100 bp upstream of the A. aeolicus glnBA operon and so is likely to be involved in the regulation of nitrogen assimilation in this organism. These results argue that the sigma(N) enhancer-dependent transcription system operates in at least one extreme environment, and that the activator and sigma(N) have coevolved.

S-methyl N-butylthiocarbamate sulfoxide: selective carbamoylating agent for mouse mitochondrial aldehyde dehydrogenase

Liver mitochondrial low-Km aldehyde dehydrogenase (ALDH2, EC 1.2.1.3), the isoform responsible for the conversion of acetaldehyde to acetate, is inhibited by the sulfoxide bioactivation products of Et2NC(O)SMe (from the alcohol aversion drug disulfiram), Pr2NC(O)SEt (the herbicide S-ethyl N,N-dipropylthiocarbamate), and BuNHC(O)SMe (from the fungicide benomyl). This study tested the hypothesis that bioactivated BuNHC(O)SMe, the most potent of these thiocarbamates, is a selective carbamoylating agent for ALDH2 of mouse liver in vivo and in vitro. [14C]BuNHC(O)SMe administered i.p. to mice labeled one principal mitochondrial protein, which cochromatographed with ALDH activity by in-gel assay after isoelectric focusing. The labeled protein was isolated by isoelectric focusing (pI 6.1) and SDS-PAGE (54 kDa) and identified as ALDH2 by sequencing of peptides from a tryptic digest. In vivo at 1.5 mg/kg, enzyme inhibition was 80%, and ALDH2 was the only mitochondrial protein labeled extensively, illustrating the outstanding potency and specificity. ALDH2 also was labeled upon incubation of mouse liver mitochondria with [14C]BuNH-C(O)SMe in the presence of microsomes (P450) and NADPH. In contrast, under similar conditions, [14C]Pr2NC(O)SEt sulfoxide labeled primarily two other proteins at approximately 58 and approximately 61 kDa, establishing a very different selectivity for the two sulfoxides. These findings are of interest relative to selective inhibitors and carbamoylating agents for ALDH2 and to alcohol aversion upon exposure to herbicides and fungicides.

The effects of hydrostatic pressure on the conformation of plasminogen

Plasminogen undergoes a large conformational change when it binds 6-aminohexanoate. Using ultraviolet absorption spectroscopy and native PAGE, we show that hydrostatic pressure brings about the same conformational change. The volume change for this conformational change is -33 mL.mol-1. Binding of ligand and hydrostatic pressure both cause the protein to open up to expose surfaces that had previously been buried in the interior.