title: Trimeric structure and conformational equilibrium of M-ficolin fibrinogen-like domain.
abstract: Ficolins are pathogen-recognition molecules in innate immune systems. The crystal structure of the human M-ficolin recognition domain (FD1) has been determined at 1.9 A resolution, and compared with that of the human fibrinogen gamma fragment, tachylectin-5A, L-ficolin and H-ficolin. The overall structure of FD1 is similar to that of the other proteins, although the peptide bond between Asp282 and Cys283, which is in a predicted ligand-binding site, is a normal trans bond, unlike the cases of the other proteins. Analysis of the pH-dependent ligand-binding activity of FD1 in solution suggested that a conformational equilibrium between active and non-active forms in the ligand-binding region, involving cis-trans isomerization of the Asp282-Cys283 peptide bond, contributes to the discrimination between self and non-self, and that the pK(a) values of His284 are 6.1 and 6.3 in the active and non-active forms, respectively.
authors.affiliation: Mitsubishi Kagaku Institute of Life Sciences (MITILS), 11 Minamiooya, Machida, Tokyo 194-8511, Japan.
authors.forename: Michikazu
authors.initials: M
authors.lastname: Tanio
authors.forename: Shin
authors.initials: S
authors.lastname: Kondo
authors.forename: Shigetoshi
authors.initials: S
authors.lastname: Sugio
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Kohno
mesh_terms: D001704:Biopolymers / Q000737:chemistry*; D005340:Fibrinogen / Q000737:chemistry*; D037102:Lectins / Q000737:chemistry*; D008958:Models, Molecular; D011487:Protein Conformation; D000097604:Ficolins
chemical_list: D001704:Biopolymers; D005340:Fibrinogen; D037102:Lectins; D000097604:Ficolins