Secondary Structure Parameters Research Articles

Structural analysis of staphylococcal enterotoxins B and C1 using circular dichroism and fluorescence spectroscopy.

Secondary and tertiary structural parameters of two functionally and serologically related proteins, staphylococcal enterotoxins B and C1, have been determined by using circular dichroism and fluorescence spectroscopy. The secondary structures derived from the respective far-UV circular dichroic spectra were 9.5% alpha-helix, 55.0% beta-pleated sheets, 16.5% beta-turns, and 19.0% random coils for enterotoxin B and 15.0% alpha-helix, 38.0% beta-pleated sheets, 25.5% beta-turns, and 21.5% random coils for staphylococcal enterotoxin C1. The values matched well with the secondary structures derived from the amino acid sequences (Chou and Fasman method). Seven antigenic sites have been predicted for both staphylococcal enterotoxins B and C1 by using the hydrophilicity and the secondary structure information. Three of these antigenic sites appear similar. Fluorescence quantum yield of the single tryptophan residue (Trp-197) of both the enterotoxins showed the tryptophan residue in staphylococcal enterotoxin B to be approximately 46% more fluorescent than in staphylococcal enterotoxin C1. Tryptophan fluorescence quenching by the surface quencher I- and the neutral quencher acrylamide revealed that the single tryptophan residue in each of the enterotoxins is buried in the protein matrix and is not accessible to the surface quencher I-. The tryptophan residue in staphylococcal enterotoxin C1 is 14% less accessible to acrylamide than in staphylococcal enterotoxin B. The data, in general, reflect several similarities and significant differences between the two related enterotoxins.

MULTIVARIATE ANALYSIS OF STRUCTURE-RELATED DATA TO EXPLAIN MILK CLOTTING ACTIVITY OF PROTEOLYTIC ENZYMES

Multivariate analysis was used for investigating the relationships between milk-clotting activity and physical/chemical properties, such as CD spectra, hydrophobicity and zeta potential, of ten proteolytic enzymes measured at six different pH values. Cluster analysis of CD data and zeta potential values classified the enzymes into five groups, i.e., three active enzyme groups and two inactive enzyme groups with respect to milk clotting activity. Classification of the enzymes into three groups, i.e., enzymes with high, medium and low milk-clotting activity, was achieved by discriminant analysis after adding the ratio of secondary structure parameters to the predictor variables. Results indicated that β-sheet, β-turn and random structure features were important for milk-clotting activity.

Biochemistry and biology of anaphylatoxins.

The molecular architecture of anaphylatoxins has been explored on several levels. Primary, secondary and tertiary structural parameters that dictate function of the C3a, C4a and C5a molecules are being elucidated with the aid of comparative sequence analyses, physical measurements and organic syntheses. Although C3a, C4a and C5a are biologically distinct mediators, as defined by their unique receptor systems, a common genetic origin is apparent from conserved features in their primary structures. Evidence is now available which suggests that similarities in the folding pattern of the anaphylatoxins may dictate a concensus conformation for each factor. We have learned from synthetic peptide studies that the binding (e.g. effector) site in anaphylatoxin molecules exists as a linear sequence contained in the C-terminal portion of the polypeptide. What is also evident is that a preferred conformation is defined for the binding site requiring a proper side chain orientation for optimal bioactivity. It is proposed that folding of the native structure stabilizes this conformation at the binding site. The binding site in C3a contains the essential residues LGLAR folded in an irregular or pseudo-beta-turn and stabilized by an adjacent alpha-helical segment. It is proposed that the alpha-helical segment influences orientation of the side chain residues in the 'binding site'. A similar model is evolving for C5a based on synthetic C5a peptides that express both spasmogenic and chemotactic activities. This helix turn model promises to be representative of an essential structural feature that determines anaphylatoxin activity. We believe that these models contribute significantly to our understanding of the molecular relationships between structure and function for these humoral mediators of inflammation.

Secondary structure of globulins from plant seeds: a re-evaluation from circular dichroism measurements

The secondary structure parameters of plant seed globulins (11S from Brassica napus L, 11S from Helianthus annuus L, IIS from Vicia faba, 7S from Phaseolus vulgaris L) have been determined from their circular dichroism spectra by the method of Provencher and Glöckner. According to this method, the proteins contain 40–50% β-sheet structure and only about 10% helical structure. We conclude, therefore, that the plant seed globulins belong to the class of β-sheet proteins. Their overall secondary structure is homologous. It is shown that the method of Provencher and Glöckner provides reasonable secondary structure parameters for proteins which are rich in β-sheet structure even if the spectral range utilized for analysis is restricted to 210–240 nm.

Beginnings and Endings in Western Art Music

Beginnings and Endings in Western Art Music. Un article de la revue Canadian University Music Review / Revue de musique des universités canadiennes (Numéro 3, 1982, p. 1-234) diffusée par la plateforme Érudit.

Conformation of gamma-crystallins of the calf lens: Effects of temperature and denaturing agents

The secondary and tertiary conformations of calf γ-crystallin were monitored by circular dichroism (CD) measurements in the near and far ultraviolet regions. The secondary structures of the various fractions of γ-crystallin do not possess any α-helix conformation as judged by the far ultraviolet CD spectra. Each of the various γ-crystallin fractions exhibited a unique and complex near ultraviolet CD spectrum, reflecting the contributions of tryptophanyl, tyrosyl and phenylalanyl residues to the optical activity. The low molecular weight β-crystallin fraction, β s, possesses its own characteristic secondary and tertiary structural parameters. β s-crystallin contains about 10% of α-helical structure and its CD wavelength profile in the near ultraviolet is different from that observed for the various γ-crystallin fractions. One per cent sodium dodecyl sulfate and 5 m-guanidine hydrochloride were very effective in the disruption of the secondary and tertiary structure of γ-crystallin as judged from the changes observed in the CD spectra. On the other hand, 8 m-urea caused only minor perturbation in the CD wavelength profile, suggesting that γ-crystallin did not denature at high urea concentration. The conformation of γ-crystallin as a function of temperature was monitored by CD measurements between −20°C and +60°C at pH values of 5·5 and 8·5 and at various protein concentrations ranging from 1 to 40 mg/ml. No significant spectroscopic changes were observed within this temperature range. The independence of the CD spectra from temperature suggests that the aromatic residues of γ-crystallin are in a rigid environment and do not possess appreciable conformational motility. Previous work Zigman and Lerman 1965 has suggested that γ-crystallin (which was classified as a “cryoprotein”) when cooled, changes its conformation in such a way as to cause precipitation. While conformational changes as a function of temperature could be detected by optical measurements in other cryoproteins, we have failed to detect such changes in γ-crystallins. The fact that γ-crystallin precipitates at relatively high concentration in a very narrow pH range as the temperature is lowered, can simply be explained as isoelectric precipitation.