A mutant complement factor H (W1183R) enhances proteolytic cleavage of von Willebrand factor by ADAMTS-13 under shear.

BACKGROUND

A loss-of-functional mutation (W1183R) in human complement factor H (CFH) is associated with complement-associated hemolytic uremic syndrome; mice carrying a similar mutation (W1206R) in CFH also develop thrombotic microangiopathy but its plasma von Willebrand factor (VWF) multimer sizes were dramatically reduced. The mechanism underlying such a dramatic change in plasma VWF multimer distribution in these mice is not fully understood.

OBJECTIVES

To determine the VWF and CFH interaction and how CFH proteins affect VWF multimer distribution.

METHODS

We employed recombinant protein expression, purification, and various biochemical and biophysical tools.

RESULTS

Purified recombinant W1183R-CFH but not wild-type (WT) CFH protein enhanced the proteolytic cleavage of both peptidyl and multimeric VWF substrates by recombinant ADAMTS-13 in a concentration-dependent manner. Microscale thermophoresis assay demonstrated that both W1183R-CFH and WT-CFH proteins bound various VWF fragments (eg, AIM-A1, A1-A2-A3, D'D3, D'D3-A1, and D'D3-A1-A2) with high affinities. Optical tweezer experiments further showed a concentration-dependent alteration in the contour length (Lc) and the persistent length (Lp) following pulling VWF-A2 domain in the presence of W1183R-CFH or WT-CFH protein. AlphaFold experiments revealed conformational changes in the VWF-A2, particularly the central region where the cleavage bond resides following addition of W1183R-CFH or WT-CFH protein.

CONCLUSION

These results demonstrate for the first time that W1183R-CFH but not WT-CFH protein enhances the proteolytic cleavage of VWF by ADAMTS-13 under shear. This may be achieved by mechanic-induced conformational changes of the central A2 domain, leading to an enhanced cleavage of Tyr1605-Met1606 bond by ADAMTS-13 under pathophysiological conditions.