title: Crystal structure of flavocetin-A, a platelet glycoprotein Ib-binding protein, reveals a novel cyclic tetramer of C-type lectin-like heterodimers.
abstract: Snake venom contains a number of the hemostatically active C-type lectin-like proteins, which affect the interaction between von Willebrand factor (vWF) and the platelet glycoprotein (GP) Ib or platelet receptor to inhibit/induce platelet activation. Flavocetin-A (FL-A) is a high-molecular mass C-type lectin-like protein (149 kDa) isolated from the habu snake venom. FL-A binds with high affinity to the platelet GP Ibalpha-subunit and functions as a strong inhibitor of vWF-dependent platelet aggregation. We have determined the X-ray crystal structure of FL-A and refined to 2.5 A resolution. This is a first elucidation of a three-dimensional structure of the platelet GP Ib-binding protein. The overall structure reveals that the molecule is a novel cyclic tetramer (alphabeta)(4) made up of four alphabeta-heterodimers related by a crystallographic 4-fold symmetry. The tetramerization is mediated by an interchain disulfide bridge between cysteine residues at the C-terminus of the alpha-subunit and at the N-terminus of the beta-subunit in the neighboring alphabeta-heterodimer. The high affinity of FL-A for the platelet GP Ib alpha-subunit could be explained by a cooperative-binding action through the multiple binding sites of the tetramer.
authors.affiliation: Institute of Applied Biochemistry, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Fukuda
authors.forename: H
authors.initials: H
authors.lastname: Mizuno
authors.forename: H
authors.initials: H
authors.lastname: Atoda
authors.forename: T
authors.initials: T
authors.lastname: Morita
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry*; D003435:Crotalid Venoms / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004220:Disulfides; D037102:Lectins / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000378:metabolism*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry; D030162:Reptilian Proteins; D017386:Sequence Homology, Amino Acid; D014757:Viper Venoms
chemical_list: D002352:Carrier Proteins; D003435:Crotalid Venoms; D004220:Disulfides; D037102:Lectins; D019038:Platelet Glycoprotein GPIb-IX Complex; D011506:Proteins; D030162:Reptilian Proteins; D014757:Viper Venoms; C402798:flavocetin A; C080995:echicetin; D002118:Calcium