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The importance of vicinal cysteines, C1669 and C1670, for von Willebrand factor A2 domain function.

ABSTRACT: The von Willebrand factor (VWF) A2 crystal structure has revealed the presence of a rare vicinal disulfide bond between C1669 and C1670, predicted to influence domain unfolding required for proteolysis by ADAMTS13. We prepared VWF A2 domain fragments with (A2-VicCC, residues 1473-1670) and without the vicinal disulfide bond (A2-DeltaCC, residues 1473-1668). Compared with A2-DeltaCC, A2-VicCC exhibited impaired proteolysis and also reduced binding to ADAMTS13. Circular dichroism studies revealed that A2-VicCC was more resistant to thermal unfolding than A2-DeltaCC. Mutagenesis of C1669/C1670 in full-length VWF resulted in markedly increased susceptibility to cleavage by ADAMTS13, confirming the important role of the paired vicinal cysteines in VWF A2 domain stabilization.

SUBMITTER: Luken BM

PROVIDER: S-EPMC2890177 | biostudies-literature | 2010 Jun

REPOSITORIES: biostudies-literature

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The importance of vicinal cysteines, C1669 and C1670, for von Willebrand factor A2 domain function.

Luken Brenda M BM Winn Luke Y N LY Emsley Jonas J Lane David A DA Crawley James T B JT

Blood 20100330 23

The von Willebrand factor (VWF) A2 crystal structure has revealed the presence of a rare vicinal disulfide bond between C1669 and C1670, predicted to influence domain unfolding required for proteolysis by ADAMTS13. We prepared VWF A2 domain fragments with (A2-VicCC, residues 1473-1670) and without the vicinal disulfide bond (A2-DeltaCC, residues 1473-1668). Compared with A2-DeltaCC, A2-VicCC exhibited impaired proteolysis and also reduced binding to ADAMTS13. Circular dichroism studies revealed ...[more]

PMID: 20354169

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Calcium stabilizes the von Willebrand factor A2 domain by promoting refolding.

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A common mechanism by which type 2A von Willebrand disease mutations enhance ADAMTS13 proteolysis revealed with a von Willebrand factor A2 domain FRET construct.

Project description:Rheological forces in the blood trigger the unfolding of von Willebrand factor (VWF) and its A2 domain, exposing the scissile bond for proteolysis by ADAMTS13. Under quiescent conditions, the scissile bond is hidden by the folded structure due to the stabilisation provided by the structural specialisations of the VWF A2 domain, a vicinal disulphide bond, a calcium binding site and a N1574-glycan.The reduced circulating high MW multimers of VWF in patients with type 2A von Willebrand disease (VWD) may be associated with mutations within the VWF A2 domain and this is attributed to enhanced ADAMTS13 proteolysis. We investigated 11 VWF A2 domain variants identified in patients with type 2A VWD. In recombinant full-length VWF, enhanced ADAMTS13 proteolysis was detected for all of the expressed variants in the presence of urea-induced denaturation. A subset of the FLVWF variants displayed enhanced proteolysis in the absence of urea. The mechanism of enhancement was investigated using a novel VWF A2 domain FRET construct. In the absence of induced unfolding, 7/8 of the expressed mutants exhibited a disrupted domain fold, causing spatial separation of the N- and C- termini. Three of the type 2A mutants were not secreted when studied within the VWF A2 domain FRET construct. Urea denaturation revealed for all 8 secreted mutants reduced unfolding cooperativity and stability of the VWF A2 domain. As folding stability was progressively disrupted, proteolysis by ADAMTS13 increased. Due to the range of folding stabilities and wide distribution of VWF A2 domain mutations studied, we conclude that these mutations disrupt regulated folding of the VWF A2 domain. They enhance unfolding by inducing separation of N- and C-termini, thereby promoting a more open conformation that reveals its binding sites for ADAMTS13 and the scissile bond.

| S-EPMC5706690 | biostudies-literature

Mechanisms by which von Willebrand disease mutations destabilize the A2 domain.

Project description:von Willebrand Factor (VWF) is an ultralong, concatameric, and adhesive glycoprotein. On short time scales, adhesiveness for platelets is activated by elongation of VWF by altered hydrodynamics at sites of hemostasis. Over longer time scales, the length of VWF is regulated by ADAMTS13 (a disintegrin and metalloprotease with a thrombospondin type 1 motif, member 13), cleavage by which in the VWF A2 domain is dependent on elongational force. Patients with von Willebrand disease type 2A present with increased bleeding due to mutations within the VWF A2 domain that enhance cleavage. We tested using temperature and force the hypothesis that von Willebrand disease mutations disrupt A2 force sensing by destabilizing the folded state. Mutations R1597W, M1528V, and E1638K reduced A2 thermal stability by 10-18 °C. M1528V and E1638K showed a marked further decrease in stability upon calcium removal. In contrast, R1597W, which resides within the A2 calcium-binding loop, exhibited similar stability in the presence and absence of calcium. Using single molecule optical tweezers and R1597W, we measured the force dependence of unfolding and refolding kinetics. In the presence of calcium, the R1597W mutation slowed the rate of refolding but had no effect on unfolding. The three mutations highlight the calcium-binding loop (R1597W), the hydrophobic core around the vicinal disulfide (M1528V), and hydrogen bonds to the ?4-less loop (E1638K), as structural features critically important to the function of A2 as a force sensor in regulating thrombogenic activity in the vasculature.

| S-EPMC3585066 | biostudies-literature

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