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PDBsum entry 1vzm
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Calcium-binding protein
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PDB id
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1vzm
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References listed in PDB file
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Key reference
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Title
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Structural evidence of a fourth gla residue in fish osteocalcin: biological implications.
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Authors
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C.Frazão,
D.C.Simes,
R.Coelho,
D.Alves,
M.K.Williamson,
P.A.Price,
M.L.Cancela,
M.A.Carrondo.
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Ref.
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Biochemistry, 2005,
44,
1234-1242.
[DOI no: ]
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PubMed id
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Abstract
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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.
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Secondary reference #1
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Title
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Purification of matrix gla protein from a marine teleost fish, Argyrosomus regius: calcified cartilage and not bone as the primary site of mgp accumulation in fish.
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Authors
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D.C.Simes,
M.K.Williamson,
J.B.Ortiz-Delgado,
C.S.Viegas,
P.A.Price,
M.L.Cancela.
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Ref.
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J Bone Miner Res, 2003,
18,
244-259.
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PubMed id
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