Journal of Biological Chemistry · 1980 · 258 citations · 19 references
Life SciencesBiochemistryMolecular BiologyBone MetabolismPost-translational ModificationProtein BiochemistryAmino Acid CompositionBone PhysiologyProtein SeparationProtein Sequence AnalysisProtein StructureProteolytic EnzymesAmino AcidsBase SubstitutionsBone Matrix BiochemistryBone Matrix ProteinsDisulfide Bond ChemistryDisulfide Bond CleavagePositionVitamin K-dependent Proteins
The study discusses the significance of finding a partially γ‑carboxylated glutamate at position 17 in the bone protein. The protein was isolated from demineralized bone by gel filtration and immunoadsorption, then its sequence was determined by automated analysis of the full protein and of tryptic and Staphylococcus aureus protease digests. The 49‑residue protein contains two γ‑carboxyglutamic acids, one disulfide bond, 4 human–calf and 23 human–swordfish substitutions, and shows that Glu‑17 is only 9 % γ‑carboxylated while residues 21 and 24 are fully γ‑carboxylated, marking the first instance of a partially γ‑carboxylated glutamate preceding a γ‑carboxyglutamate.
The gamma-carboxyglutamate-containing protein from human bone has been isolated from proteins released upon demineralization of bone by using a combination of gel filtration and immunoadsorption onto a column of immobilized antibody. The sequence of the protein has been determined by automatic sequence analysis of the whole protein and of peptides isolated from tryptic and Staphylococcus aureus protease digests. The protein consists of 49 amino acids in a single polypeptide chain, contains 2 residues of gamma-carboxyglutamic acid, and a single disulfide bond. There are 4 translational substitutions between the human and calf bone proteins and 23 translational substitutions between the human and swordfish bone proteins. Glu-17 was found to be only 9% gamma-carboxylated, while sequence positions 21 and 24 are fully gamma-carboxylated. The identification of glutamic acid at position 17 represents the first instance where a partially gamma-carboxylated glutamate has been found in a sequence position which is to the NH2-terminal side of a gamma-carboxyglutamate residue. The possible significance of this observation is discussed.
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