title: The secondary structure of the von Willebrand factor type A domain in factor B of human complement by Fourier transform infrared spectroscopy. Its occurrence in collagen types VI, VII, XII and XIV, the integrins and other proteins by averaged structure predictions.
abstract: The type A domain of the von Willebrand Factor is found also in the complement proteins factor B (FB), C2, CR3 and CR4, the integrins, collagen types VI, VII, XII and XIV, and other proteins. FB is a component of the alternative pathway of the complement system of immune defence, and is cleaved into the fragments Bb and Ba during complement activation. Bb contains a von Willebrand Factor type A (vWF) domain of unknown secondary structure and a serine proteinase (SP) domain, whereas Ba contains three short consensus repeat/complement control protein (SCR/CCP) domains. Fourier transform infrared (FT-IR) spectroscopy on a recombinant vWF domain and on FB and its Bb and Ba fragments shows a broad amide I band. In H2O buffer, second derivative spectra of the amide I band show subcomponents at 1654 to 1657 cm-1, which is typical of alpha-helix, and at 1676 to 1685 cm-1 and 1636 to 1637 cm-1, which are typical of beta-strand. alpha-Helix was detected in the vWF domain, the Bb fragment and FB, and the proportion of alpha-helix present decreased in that order. This shows that the vWF domain contains appreciable amounts of alpha-helix, while the SP and SCR/CCP domains are almost entirely beta-sheet in their secondary structures. Quantitative integration of the vWF FT-IR spectrum showed that this contained 31% alpha-helix and 36% beta-sheet. In 2H2O buffer, the alpha-helix content in the vWF domain is sensitive to the solvent, while the beta-sheet content is less so. An alignment of 75 vWF type A sequences from 25 proteins was used for averaged secondary structure predictions of the total length of 206 residues by the Robson and Chou-Fasman methods. In support of the FT-IR analysis, a total of at least five well-predicted alpha-helices (35% of residues) and at least five well-predicted beta-strands (21% of residues) were identified by both predictive methods, all of which were interspersed by regions of coil or turn conformations. Eight of the ten predicted alpha-helices and beta-strands form an alternating arrangement with each other. Since the predicted alpha-helices are mostly amphipathic, and since the alpha-helix FT-IR band is sensitive to solvent, the alpha-helices are inferred to be on the protein surface.(ABSTRACT TRUNCATED AT 400 WORDS)
authors.affiliation: Department of Biochemistry, Royal Free Hospital School of Medicine, London, U.K.
authors.forename: S J
authors.initials: SJ
authors.lastname: Perkins
authors.forename: K F
authors.initials: KF
authors.lastname: Smith
authors.forename: S C
authors.initials: SC
authors.lastname: Williams
authors.forename: P I
authors.initials: PI
authors.lastname: Haris
authors.forename: D
authors.initials: D
authors.lastname: Chapman
authors.forename: R B
authors.initials: RB
authors.lastname: Sim
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003094:Collagen / Q000737:chemistry; D011415:Complement Factor B / Q000737:chemistry*; D006023:Glycoproteins / Q000737:chemistry; D006801:Humans; D016023:Integrins / Q000737:chemistry; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D017550:Spectroscopy, Fourier Transform Infrared; D014841:von Willebrand Factor / Q000737:chemistry*
chemical_list: C054447:COL14A1 protein, human; D006023:Glycoproteins; D016023:Integrins; D010446:Peptide Fragments; D011994:Recombinant Proteins; D014841:von Willebrand Factor; D003094:Collagen; D011415:Complement Factor B