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Divalent cation-dependent structure in the platelet membrane glycoprotein Ia-IIa (VLA-2) complex
W D Staatz1, K J Peters, S A Santoro
1Department of Pathology, Washington University School of Medicine, St. Louis, MO 63110.
Biochemical and Biophysical Research Communications
|April 16, 1990
Summary
Magnesium (Mg++) and calcium (Ca++) ions stabilize distinct structures within the platelet glycoprotein Ia-IIa (VLA-2) complex, influencing its collagen-binding ability and susceptibility to proteolysis.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Platelet adhesion to collagen is mediated by the glycoprotein Ia-IIa (VLA-2) complex.
- Magnesium (Mg++)-dependent platelet adhesion to collagen is inhibited by calcium (Ca++).
- This suggests separate Mg++ and Ca++ binding sites stabilize different VLA-2 complex structures.
Purpose of the Study:
- To provide evidence for distinct Mg++ and Ca++ stabilized structures within the VLA-2 complex.
- To investigate how these divalent cations affect the VLA-2 complex's collagen-binding and proteolytic properties.
Main Methods:
- Purified platelet Ia-IIa (VLA-2) complex was subjected to limited proteolytic digestion.
- Digestion was performed in the presence of Mg++, Ca++, a combination of both, or EDTA.
- Resulting peptides were mapped using one- and two-dimensional SDS-PAGE.
Main Results:
- Unique tryptic peptide patterns were observed under each divalent cation condition.
- Mg++ and Ca++ binding resulted in different structural conformations of the VLA-2 complex.
- These structural differences correlated with changes in collagen binding and proteolytic susceptibility.
Conclusions:
- Mg++ and Ca++ stabilize distinct structural states of the VLA-2 complex.
- These cation-dependent structures modulate VLA-2's interaction with collagen and its susceptibility to enzymatic cleavage.