Physical Characteristics of von Willebrand Factor Binding with Platelet Glycoprotein Ibɑ Mutants at Residue 233 Causing Various Biological Functions

Abstract

Glycoprotein (GP: HIS1-PRO265) Ibα is a receptor protein expressed on the surface of the platelet. Its N-terminus domain binds with the A1 domain (ASP1269-PRO1472) of its ligand protein von Willebrand factor (VWF) and plays a unique role for platelet adhesion under blood flow conditions. Single amino acid substitutions at residue 233 from Glycine(G) to Alanine(A), Aspartic acid(D), or Valine(V) are known to cause bio-chemically distinct functional alterations known as equal, loss, and gain of function, respectively. However, the underlying physical characteristics of VWF binding with GPIbα in wild type and the three mutants exerting different biological functions are unclear. Here, we aimed to test the hypothesis: biological characteristics of macromolecules is influenced by small changes in physical parameters. The position coordinates and velocity vectors of all atoms and water molecules constructing the wild type and the three mutants of GPIbα (G233A, G233D, and G233V) bound with VWF were calculated every 2 x 10-15 sec using the CHARMM (Chemistry at HARvard Macromolecular Mechanics) force field for 9 x 10-10 sec. Six salt bridges were detected for longer than 50% of the calculation period for the wild-type model generating a non-covalent binding energy of -1096±137.6 kcal/mol. In contrast, only 4 pairs of salt bridges were observed in G233D mutant with a non-covalent binding energy of -865±139. For G233A and G233V, there were 6 and 5 pairs of salt bridges generating -929.8±88.5 and -989.9±94.0 kcal/mol of non-covalent binding energy, respectively. Our molecular dynamic simulation showing lower probability of salt bridge formation with less non-covalent binding energy between VWF binding with the biologically loss of function G233D mutant of GPIbα as compared to wild-type, equal function, and gain of function mutant suggest that biological functions of macromolecules such as GPIbα are influenced by their small changes in physical characteristics.

Different Physical Parameters in the Bonds between Platelet Glycoprotein Ibalpha with von Willebrand factor and with Coagulant Factor XI -Results from the Molecular Dynamic Simulation-

“…24 The lower non-covalent binding energy in GPIba-VWF bond was also shown in G233D mutant of GPIba. 25 Our results showing the structural stability with more noncovalent binding energy generated in VWF-GPIba bonds as compared to FXI-GPIba shown here further support the specific physical characteristics of VWF-GPIba mediating specific biological function.…”

“…23 Moreover, the validity of calculation results were also confirmed by the prediction of lower binding energy between the loss-of-function single point mutation (G233D) of GPIba with VWF. 24,25 The MD simulation could be applied to identify the specific physical characteristics of the VWF-GPIba bond in comparison with other protein bonds such as GPIba binding with coagulant proteins. The platelet GPIba is known to bind with various coagulant proteins such as thrombin, and coagulation factor XI (FXI).…”