The vitamin K-dependent blood coagulation factor IX as well as several
extracellular regulatory proteins require vitamin K for the posttranslational
synthesis of γ-carboxyglutamic acid, an amino acid clustered in the
N-terminal Gla domain of these proteins [1,2]. The Gla domain is a membrane
binding motif which, in the presence of calcium ions, interacts with
phospholipid membranes that include phosphatidylserine.
The 3D structure of the Gla domain has been solved (see for example
<PDB:1CFH>) [3,4]. Calcium ions induce conformational changes in the Gla
domain and are necessary for the Gla domain to fold properly. A common
structural feature of functional Gla domains is the clustering of N-terminal
hydrophobic residues into a hydrophobic patch that mediates interaction with
the cell surface membrane .
Proteins known to contain a Gla domain are listed below:
A number of plasma proteins involved in blood coagulation. These proteins
are prothrombin, coagulation factors VII, IX and X, proteins C, S, and Z.
Two proteins that occur in calcified tissues: osteocalcin (also known as
bone-Gla protein, BGP), and matrix Gla-protein (MGP).
Cone snail venom peptides: conantokin-G and -T, and conotoxin GS .
The pattern we developed start with the conserved Gla-x(3)-Gla-x-Cys motif
found in the middle of the domain which seems to be important for substrate
recognition by the carboxylase  and end with the last conserved position of
the domain (an aromatic residue). We also developed a profile that covers the
whole Gla domain.
All glutamic residues present in the domain are potential carboxylation
sites; in coagulation proteins, all are modified to Gla, while in BGP and MGP
some are not.
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