Gla glances at proteins
http://www.100md.com
《血液学杂志》
CARDIOVASCULAR RESEARCH INSTITUTE MAASTRICHT
Our view on Gla domains can no longer be limited to their phospholipid-binding properties because they cointeract directly with proteins, and as is shown for protein S in this issue, these interactions are mediated by distinct faces on the Gla domain.
For a long time, -carboxyglutamic acid (Gla)–rich modules were considered solely to be membrane anchors that enabled vitamin K–dependent clotting factors to interact with (negatively charged) phospholipid surfaces. On these surfaces, the enzyme-cofactor complexes can effectively exert their pro- and anticoagulant activities.
In the late 1970s, 2 models of Gla-binding to phospholipids were proposed: the ionic interaction model assumed that Gla-bound Ca2+ ions were involved in negatively charged membrane binding through electrostatic interactions, and the chelation model proposed coordination of Ca2+ between one Gla residue and 2 negatively charged phosphatidylserine head groups. In 1995, Sunnerhagen et al1 described Ca2+-induced exposure of hydrophobic residues in the -loop to be essential for membrane binding.1 Recently, a solution to this debate emerged as a scientific compromise in which a combination of phosphatidylserine head group-binding to Gla-bound Ca2+ ions (and Gla residues) and embedding of hydrophobic residues in the phospholipid membrane were unveiled as determinants of Glamembrane interaction.2
In the past decade, however, increasing evidence emerged for interactions of Gla domains with ligands other than phospholipids. Examples include binding of the Gla domains of activated protein C (APC) to the endothelial cell protein C receptor (EPCR),3 of activated factor IX (FIXa) to activated factor VIII (FVIIIa),4 and of factor X to tissue factor-factor VIIa.5
Model of the N-terminal 116 residues of protein S that make up the Gla domain (residues 1-46), thrombin-sensitive region (residues 47-75), and the first epidermal growth factor–like region (residues 76-116), represented as solvent-accessible surface. Shown in magenta and yellow are the residues of face 1 that are important for phospholipid binding (Gln10, Asn33, Asp34, Pro35, Gla36, Tyr39). In cyan and yellow are the residues of face 2 involved in the interaction with APC (Leu21, Asn23, Lys24, Arg28, Asn33, Asp34, Pro35, Tyr41, Leu45); the yellow residues are present on both faces. See the ribbon diagram in the article beginning on page 122. Reprinted with the permission of Gerry A. F. Nicolaes, Cardiovascular Research Institute Maastricht, The Netherlands.
In this issue, Saller and colleagues identified 2 faces on the Gla domain of protein S that mediate interactions with phospholipids and APC, respectively. The clue for unraveling these faces followed from the application of a protein S molecule, in which the Gla domain was exchanged for the Gla domain of prothrombin. This prothrombin–protein S chimera retained phospholipid binding capacity but did not act as a cofactor for APC, explained by a loss of interaction with APC. Using homology modeling and differences in sequence between the Gla domains of prothrombin and protein S, 2 opposite faces were postulated; the solvent-exposed residues were either involved in the interaction with phospholipids (face 1) or APC (face 2). In a solvent-accessible surface model it is clearly shown that the important residues of the faces are exposed on opposite sides of the Gla domain of protein S (figure). Replacing face 2 in protein S with the amino acids from prothrombin resulted in loss of APC-cofactor activity, and reintroducing the faces from protein S in the prothrombin–protein S chimera regained previously lost APC-cofactor activity, and therefore likely the interaction with APC.
Protein S is a multimodular protein that is special among the vitamin K–dependent coagulation protein family as it is not a precursor to an enzyme. It is a multifunctional protein and is most well known for its cofactor activity to APC. In addition, protein S regulates thrombin formation in the absence of APC, is involved in inflammatory mediation and apoptosis pathways, and exhibits neuroprotective effects.6
In aid of structure-function analysis of these different activities of protein S, it is important to locate regions or residues within protein S that govern specific activities. For the first time in protein S, such residues are identified, which may serve as a stepping stone for unraveling mechanistic bases that differentiate between multiple functions of this essential protein.
References
Sunnerhagen M, Forsen S, Hoffren AM, Drakenberg T, Teleman O, Stenflo J. Structure of the Ca(2+)-free Gla domain sheds light on membrane binding of blood coagulation proteins. Nat Struct Biol. 1995;2: 504-509.
Huang M, Rigby AC, Morelli X, et al. Structural basis of membrane binding by Gla domains of vitamin K-dependent proteins. Nat Struct Biol. 2003;10: 751-756.
Regan LM, Mollica JS, Rezaie AR, Esmon CT. The interaction between the endothelial cell protein C receptor and protein C is dictated by the gamma-carboxyglutamic acid domain of protein C. J Biol Chem. 1997;272: 26279-26284.
Blostein MD, Furie BC, Rajotte I, Furie B. The Gla domain of factor IXa binds to factor VIIIa in the tenase complex. J Biol Chem. 2003;278: 31297-31302.
Huang Q, Neuenschwander PF, Rezaie AR, Morrissey JH. Substrate recognition by tissue factor-factor VIIa: evidence for interaction of residues Lys165 and Lys166 of tissue factor with the 4-carboxyglutamate-rich domain of factor X. J Biol Chem. 1996;271: 21752-21757.
Rezende SM, Simmonds RE, Lane DA. Coagulation, inflammation, and apoptosis: different roles for protein S and the protein S-C4b binding protein complex. Blood. 2004;103: 1192-1201.(Tilman M. Hackeng)
Our view on Gla domains can no longer be limited to their phospholipid-binding properties because they cointeract directly with proteins, and as is shown for protein S in this issue, these interactions are mediated by distinct faces on the Gla domain.
For a long time, -carboxyglutamic acid (Gla)–rich modules were considered solely to be membrane anchors that enabled vitamin K–dependent clotting factors to interact with (negatively charged) phospholipid surfaces. On these surfaces, the enzyme-cofactor complexes can effectively exert their pro- and anticoagulant activities.
In the late 1970s, 2 models of Gla-binding to phospholipids were proposed: the ionic interaction model assumed that Gla-bound Ca2+ ions were involved in negatively charged membrane binding through electrostatic interactions, and the chelation model proposed coordination of Ca2+ between one Gla residue and 2 negatively charged phosphatidylserine head groups. In 1995, Sunnerhagen et al1 described Ca2+-induced exposure of hydrophobic residues in the -loop to be essential for membrane binding.1 Recently, a solution to this debate emerged as a scientific compromise in which a combination of phosphatidylserine head group-binding to Gla-bound Ca2+ ions (and Gla residues) and embedding of hydrophobic residues in the phospholipid membrane were unveiled as determinants of Glamembrane interaction.2
In the past decade, however, increasing evidence emerged for interactions of Gla domains with ligands other than phospholipids. Examples include binding of the Gla domains of activated protein C (APC) to the endothelial cell protein C receptor (EPCR),3 of activated factor IX (FIXa) to activated factor VIII (FVIIIa),4 and of factor X to tissue factor-factor VIIa.5
Model of the N-terminal 116 residues of protein S that make up the Gla domain (residues 1-46), thrombin-sensitive region (residues 47-75), and the first epidermal growth factor–like region (residues 76-116), represented as solvent-accessible surface. Shown in magenta and yellow are the residues of face 1 that are important for phospholipid binding (Gln10, Asn33, Asp34, Pro35, Gla36, Tyr39). In cyan and yellow are the residues of face 2 involved in the interaction with APC (Leu21, Asn23, Lys24, Arg28, Asn33, Asp34, Pro35, Tyr41, Leu45); the yellow residues are present on both faces. See the ribbon diagram in the article beginning on page 122. Reprinted with the permission of Gerry A. F. Nicolaes, Cardiovascular Research Institute Maastricht, The Netherlands.
In this issue, Saller and colleagues identified 2 faces on the Gla domain of protein S that mediate interactions with phospholipids and APC, respectively. The clue for unraveling these faces followed from the application of a protein S molecule, in which the Gla domain was exchanged for the Gla domain of prothrombin. This prothrombin–protein S chimera retained phospholipid binding capacity but did not act as a cofactor for APC, explained by a loss of interaction with APC. Using homology modeling and differences in sequence between the Gla domains of prothrombin and protein S, 2 opposite faces were postulated; the solvent-exposed residues were either involved in the interaction with phospholipids (face 1) or APC (face 2). In a solvent-accessible surface model it is clearly shown that the important residues of the faces are exposed on opposite sides of the Gla domain of protein S (figure). Replacing face 2 in protein S with the amino acids from prothrombin resulted in loss of APC-cofactor activity, and reintroducing the faces from protein S in the prothrombin–protein S chimera regained previously lost APC-cofactor activity, and therefore likely the interaction with APC.
Protein S is a multimodular protein that is special among the vitamin K–dependent coagulation protein family as it is not a precursor to an enzyme. It is a multifunctional protein and is most well known for its cofactor activity to APC. In addition, protein S regulates thrombin formation in the absence of APC, is involved in inflammatory mediation and apoptosis pathways, and exhibits neuroprotective effects.6
In aid of structure-function analysis of these different activities of protein S, it is important to locate regions or residues within protein S that govern specific activities. For the first time in protein S, such residues are identified, which may serve as a stepping stone for unraveling mechanistic bases that differentiate between multiple functions of this essential protein.
References
Sunnerhagen M, Forsen S, Hoffren AM, Drakenberg T, Teleman O, Stenflo J. Structure of the Ca(2+)-free Gla domain sheds light on membrane binding of blood coagulation proteins. Nat Struct Biol. 1995;2: 504-509.
Huang M, Rigby AC, Morelli X, et al. Structural basis of membrane binding by Gla domains of vitamin K-dependent proteins. Nat Struct Biol. 2003;10: 751-756.
Regan LM, Mollica JS, Rezaie AR, Esmon CT. The interaction between the endothelial cell protein C receptor and protein C is dictated by the gamma-carboxyglutamic acid domain of protein C. J Biol Chem. 1997;272: 26279-26284.
Blostein MD, Furie BC, Rajotte I, Furie B. The Gla domain of factor IXa binds to factor VIIIa in the tenase complex. J Biol Chem. 2003;278: 31297-31302.
Huang Q, Neuenschwander PF, Rezaie AR, Morrissey JH. Substrate recognition by tissue factor-factor VIIa: evidence for interaction of residues Lys165 and Lys166 of tissue factor with the 4-carboxyglutamate-rich domain of factor X. J Biol Chem. 1996;271: 21752-21757.
Rezende SM, Simmonds RE, Lane DA. Coagulation, inflammation, and apoptosis: different roles for protein S and the protein S-C4b binding protein complex. Blood. 2004;103: 1192-1201.(Tilman M. Hackeng)