The molecular weight determination of proteins and glycoproteins of RNA enveloped viruses by polyacrylamide gel electrophoresis in SDS

Relating glycoprotein structural heterogeneity to function - insights from native mass spectrometry

Glycosylation is the most complex and prevalent protein modification that influences attributes ranging from cellular localization and signaling to half-life and proteolysis. Glycoconjugates are fundamental for cellular function and alterations in their structure are often observed in pathological states. Most biotherapeutic proteins are glycosylated, which influences drug safety and efficacy. Therefore, the ability to characterize glycoproteins is important in all areas of biomolecular and medicinal research. Here we discuss recent advances in native mass spectrometry that have significantly improved our ability to characterize heterogeneous glycoproteins and to relate glycan structure to protein function.

Characterization of the novel antifungal chitosanase PgChP and the encoding gene from Penicillium chrysogenum

The protein PgChP is a new chitosanase produced by Penicillium chrysogenum AS51D that showed antifungal activity against toxigenic molds. Two isoforms were found by SDS-PAGE in the purified extract of PgChP. After enzymatic deglycosylation, only the smaller isoform was observed by SDS-PAGE. Identical amino acid sequences were obtained from the two isoforms. Analysis of the molecular mass by electrospray ionization-mass spectrometry revealed six major peaks from 30 to 31 kDa that are related to different levels of glycosylation. The pgchp gene has 1,146 bp including four introns and an open reading frame encoding a protein of 304 amino acids. The translated open reading frame has a predicted mass of 32 kDa, with the first 21 amino acids comprising a signal peptide. Two N glycosylation consensus sequences are present in the protein sequence. The deduced sequence showed high identity with fungal chitosanases. A high level of catalytic activity on chitosan was observed. PgChP is the first chitosanase described from P. chrysogenum. Given that enzymes produced by this mold species are granted generally recognized as safe status, PgChP could be used as a food preservative against toxigenic molds and to obtain chitosan oligomers for food additives and nutraceuticals.

Glycoprotein-surfactant interactions: A calorimetric and spectroscopic investigation of the phytase-SDS system

The interactions of sodium dodecyl sulfate (SDS) and two glyco-variants of the enzyme phytase from Peniophora lycii were investigated. One variant (Phy) was heavily glycosylated while the other (dgPhy) was enzymatically deglycosylated. Effects at 24 degrees C of titrating SDS to Phy and dgPhy were studied by Isothermal Titration Calorimetry (ITC) and Synchrotron Radiation Circular Dichroism (SRCD) spectroscopy. Comparisons of results for the two variants were used to elucidate glycan-surfactant interrelationships. The CD spectra suggested that both the native and the SDS-denatured states of the two variants were mutually similar, and hence that the denaturation process was structurally equivalent for the two glyco-variants. The denatured state was far from fully unfolded and probably retained a substantial content of native-like structure. Furthermore, it was found that the glycans brought about only a small increase in the resistance towards SDS induced denaturation. The SDS concentration required to denature half of the protein molecules differed less than 1 mM for the two variants. The affinity for SDS of both variants was unusually low. The amount of bound SDS (w/w) at different stages of the binding isotherm was 3-10 times lower than that reported for the most previously investigated globular proteins. Analysis of the relative affinity of the glycan and peptide moieties suggested that the carbohydrates bind much less surfactant. At saturation, glycans adsorbed about half as much SDS (in g/g) as the peptide moiety of Phy and about five times less than average proteins.

Proteins of hepatitis B surface antigen

Purified 22-nm forms of hepatitis B surface antigen (Hbsag) representing the three major antigenic subtypes (adw, ayw, and adr) were analyzed for their constituent polypeptides by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. No consistent difference in either the number or relative distributions of the polypeptides was observed for the various subtypes. Seven polypeptides were designated as P-1 through P-7 in order of their decreasing mobilities. By comparison with protein standards, their molecular weights were estimated as 23, 29.5, 36, 41.5, 53.5, 72, and 97 thousand. The P-1 and P-2 components represented the major polypeptides; P-2 and P-5 might by glycoproteins, based on their reaction with periodic acid-Shiff reagent. Each polypeptide contains cysteine residues. HBSAg was radiolabeled with 3H or 14C by reductive methylation or iodinated with 125I by the chloramine-T or lactoperoxidase procedures. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of labeled HBSAg yielded patterns identical to those obtained with protein stain. Comparison of HBSAg labeled by the chloramine-T and lactoperoxide procedures indicated that there was no distinction between internal or external components within the 22-nm structure.

Purification and biophysical properties of human coronavirus 229E

Coronavirus 229E was grown to high titers in diploid fibroblast cells under medium containing twice the normal concentrations of amino acids and vitamins. Growth curves showed maximum virus production at multiplicities of infection of 0.1 and 1; maximum titers of intracellular virus occurred at 22–24 hr and of extracellular virus at 26 hr postadsorption. Tube infectivity titers ranged from 109.0–109.5 TCID50/ml and plaque titers from 1010.2–1010.9 y PFU/ml at the time of peak virus production, when no cytopathology was evident. Virus titer dropped rapidly between 26 and 56 hr, coincident with increasing cytopathology. A single precipitin band was observed in immunodiffusion and immunoelectrophoresis between concentrated virus preparations and antiserum to purified 229E. Neuraminidase and hemagglutinin assays were negative. Virus was purified by two procedures: adsorption to and elution from human “0” erythrocytes and CaHPO4 gel followed by equilibrium sucrose gradient centrifugation, and PEG precipitation followed by equilibrium glycerol/tartrate gradients and rate zonal sucrose or glycerol/tartrate gradients. Final lots of purified virus containing <0.02% of the crude tissue culture proteins had absorption maxima at 256 nm and minima at 241.2 nm and a mean extinction coefficient of E 1cm1% = 54.3 at 256 nm. The fully corrected sedimentation coefficient for the intact virion was S 20,v0 = 381 S. PAGE by different techniques revealed seven polypeptides of mean apparent molecular weights between 16,900 and 196,100. Six contained carbohydrate and one contained lipid. Electropherograms of 3H- and 14C-labeled virus were identical to those of stained gels. Two glycoproteins constituting 25% of the virion protein were identified by bromelin digestion as the spike proteins. The density in sucrose and in potassium tartrate was 1.18 g/ml for the virion and 1.15 g/ml for the “despiked” particle.

Nonspecific acid phosphatase from Schizosaccharomyces pombe. Purification and physical chemical properties

Repressible nonspecific acid phosphatase from Schizosaccharomyces pombe was purified to apparent homogeneity, as ascertained from ultracentrifugal, electrophoretic, and chromatographic data. The native protein has a molecular weight of 383,000 as determined by sucrose density gradient centrifugation and 381,000 as determined by gel filtration. The native protein can be dissociated in the presence of 8 M urea-1% sodium dodecyl sulfate into sub-units possessing an approximate molecular weight of 104,000. Neutral sugars account for about 66% of the total molecular weight and contribute to the high solubility and some of the other physical properties of this enzyme. Purified enzyme preparations have a Km for 4-nitrophenyl phosphate of 0.17 mM and a broad substrate specificity, but do not show diesterase activity. Phosphate and sulfate are competitive inhibitors. The enzyme is inactivated at neutral and alkaline pH and at relatively low temperatures. Mannose and galactose was found as the main components of the carbohydrate moiety; glucosamine was present in lower amounts. The amino acid analysis revealed a high content of aspartate, threonine, and serine; no sulfhydryl group could be detected. Pi is released in stoichiometric amount (1 mol per enzyme monomer) on protein digestion.

Thyroglobulin messenger RNA: translation of a 33-S mRNA into a peptide immunologically related to thyroglobulin

Poly(UC)--Sepharose chromatography of the RNA extracted from a thyroid fraction sedimenting between 800 X g and 27000 X g allows the purification of two RNA fractions amounting each to 1% of the applied material. The first one is loosely bound to the column from which it is eluted at 25 degrees C. It is mainly composed of 16-S and 12-S RNA comprising no poly(A) sequences. This could correspond to mitochondrial rRNA. The second one, which is eluted at 50 degrees C, is poly(A)-rich and represents 33-S and 17--18-S RNA species. The 33-S RNA resists heating at 80 degrees C, suggesting that it is composed of one polynucleotide chain. When injected into Xenopus oocytes, the 33-S RNA specifically promotes the synthesis of a peptide with an apparent molecular weight of 185000 and an apparent sedimentation coefficient of 10-S. This peptide is immunologically related to thyroglobulin and could represent its main precursor. Under the conditions tested it does not polymerize spontaneously into 19-S thyroglobulin, suggesting that assembly of the molecule could require specific, post-translational alterations of the precursor and/or the presence of additional lighter subunits.

Strain-specific degradation of a viral glycoprotein in Newcastle disease virus-infected cells

In cells infected with mesogenic or lentogenic strain of Newcastle disease virus the level of neuraminidase and hemagglutinin activities sharply decreased after the addition of cycloheximide. With two velogenic strains such decreases did not occur. The infected cells were labelled with 14C-amino acids (leucine or valine) and further incubated with an excess of unlabelled precursor. Polyacrylamide gel analysis revealed a decrease of the peak correspondig to the "large" glycoprotein after the chase in cells infected with meso- or lentogenic strain (Beaudette, B1). In the cells infected with velogenic strains (Italia, Herts) no such decrease was observed. The degradation of the "large" glycoprotein as the cause of the decrease of hemagglutinin and neuraminidase activities in cycloheximide-treated cells and its possible relation to virulence is discussed.

Inhibition of glycosylation of the influenza virus hemagglutinin

d-Glucosamine and 2-deoxy-d-glucose interfere with the biosynthesis of the hemagglutinin glycoproteins. With increasing inhibitor concentrations a progressive decrease in size of the precursor HA and the cleavage products, HA(1) and HA(2) can be observed. The shift in molecular weight is paralleled by a decrease of the carbohydrate content. This was shown by labeling studies with radioactive sugars which revealed that the inhibitors block the incorporation into glycoproteins, whereas they have no or only slight effects on the uptake and activation of sugars. Under conditions of maximal inhibition, the hemagglutinin proteins lack all or most of their carbohydrates. These findings indicate that the inhibitory effect of d-glucosamine and 2-deoxy-d-glucose is due to an impairment of glycosylation. When glycosylation is inhibited, the precursor polypeptide is synthesized at normal rates. Its cleavage products, however, are very heterogeneous. This suggests that carbohydrate protects the hemagglutinin from proteolytic degradation.