PDBsum entry 1vzm

Calcium-binding protein

PDB id: 1vzm

Contents

Protein chains

43 a.a. *

Metals

_MG ×8

Waters ×191

* Residue conservation analysis

PDB id:

1vzm

Name:

Calcium-binding protein

Title:

Osteocalcin from fish argyrosomus regius

Structure:

Osteocalcin. Chain: a, b, c

Source:

Argyrosomus regius. Meagre. Organism_taxid: 172269

Resolution:

1.40Å R-factor: 0.192 R-free: 0.235

Authors:

C.Frazao,D.C.Simes,R.Coelho,D.Alves,M.K.Williamson,P.A.Price, M.L.Cancela,M.A.Carrondo

Key ref:

C.Frazão et al. (2005). Structural evidence of a fourth Gla residue in fish osteocalcin: biological implications. Biochemistry, 44, 1234-1242. PubMed id: 15667217 DOI: 10.1021/bi048336z

Date:

21-May-04 Release date: 10-Sep-04

Protein chains

Q800Y1  (OSTCN_ARGRE) -  Osteocalcin from Argyrosomus regius

Seq: 97 a.a.

Struc: 43 a.a.*

* PDB and UniProt seqs differ at 4 residue positions (black crosses)

DOI no: 10.1021/bi048336z

Biochemistry 44:1234-1242 (2005)

PubMed id: 15667217

Structural evidence of a fourth Gla residue in fish osteocalcin: biological implications.

C.Frazão, D.C.Simes, R.Coelho, D.Alves, M.K.Williamson, P.A.Price, M.L.Cancela, M.A.Carrondo.

ABSTRACT

Osteocalcin is a small (45 amino acids) secreted protein found to accumulate in bone and dentin of many organisms by interacting with calcium and hydroxyapatite, through the presence of three gamma-carboxylated residues. In this work, we describe the first X-ray crystal structure for a nonmammalian osteocalcin, obtained at 1.4 A resolution, purified from the marine teleost fish Argyrosomus regius. The three-dimensional fit between the A. regius structure and that of the only other known X-ray structure, the porcine osteocalcin, revealed a superposition of the Calpha atoms of their metal chelating residues, Gla and Asp, showing that their spatial distribution is consistent with the interatomic distances of calcium cations in the hydroxyapatite crystals. In both structures, the protein forms a tight globular arrangement of their three alpha-helices while the remaining residues, at N- and C-terminal regions, have essentially no secondary structure characteristics. This study revealed the presence of a fourth gamma-carboxylation at Glu(25), not previously detected in the structure of the porcine osteocalcin or in any other of the sequentially characterized mammalian osteocalcins (human, cow, and rat). A confirmation of the fourth Gla residue in A. regius osteocalcin was achieved via LC-MS analysis. These four doubly charged residues are, together with Asp(24), concentrated in a common surface region located on the same side of the molecule. This further suggests that the known high affinity of osteocalcin for bone mineral may be derived from the clustering of calcium binding sites on this surface of the molecules.