title: Binding of a C-terminal fragment (residues 369 to 435) of vitamin D-binding protein to actin.
abstract: The vitamin D-binding protein (DBP) binds to monomeric actin with high affinity. The variation in DBP isoforms is due to genetic polymorphism and varying glycosylation. To obtain a homogeneous preparation, the cDNA for human DBP and truncations thereof were cloned and various systems were applied for heterologous bacterial and yeast expression. The full-length protein and the N- and C-terminal halves of DBP remained insoluble probably because the protein did not fold to its native three-dimensional structure due to formation of accidental intra- and inter-molecular disulfide bonds during expression in bacteria or yeast. This problem was overcome by cloning of a C-terminal fragment comprising residues 369 to 435 that did not contain disulfide bonds and was completely soluble. Binding of the C-terminal fragment to monomeric actin was demonstrated by comigration with actin during native polyacrylamide gel electrophoresis and surface plasmon resonance, however, at considerably lower affinity than full-length DBP. This suggests that in addition to the C-terminal amino acid sequence other parts (amino acid residues or sugar moieties) of DBP participate in actin binding. The C-terminal fragment was found to inhibit denaturation of actin and to decrease the rate of actin polymerisation both at the barbed and at the pointed end in a concentration-dependent manner. According to a quantitative analysis of the polymerisation kinetics, association of actin monomers to nucleate filaments was not prevented by binding of the C-terminal fragment to actin. These data suggest that the sites on the surface of actin that are involved in actin nucleation and elongation are different.
authors.affiliation: Department of Anatomy and Embryology, Ruhr-University Bochum, D-44780 Bochum, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Buch
authors.forename: Dagmar
authors.initials: D
authors.lastname: Gremm
authors.forename: Albrecht
authors.initials: A
authors.lastname: Wegner
authors.forename: Hans Georg
authors.initials: HG
authors.lastname: Mannherz
mesh_terms: D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D018360:Crystallography, X-Ray; D017931:DNA Primers / Q000235:genetics; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011108:Polymers / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D011817:Rabbits; D016415:Sequence Alignment; D020349:Surface Plasmon Resonance; D014809:Vitamin D-Binding Protein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D000199:Actins; D017931:DNA Primers; D010446:Peptide Fragments; D011108:Polymers; D014809:Vitamin D-Binding Protein