Summary
Two recombinant expression libraries containing small (300-600 base pairs) cDNA fragments
of von Willebrand Factor (vWF) were screened in order to map the epitope of monoclonal
antibodies (MAbs) to vWF. Among eleven MAbs tested, seven were effectively mapped.
The epitopes of MAbs 418 and 522, which inhibit the binding of vWF to Factor VIII
(FVIII), were localized between Leu 2 and Arg 53 and between Glu 35 and He 81 of the
vWF subunit respectively, within the N-terminal trypsin fragment called SpIII-T4 [amino
acids (aa) 1-272] which contains a binding domain for FVIII. The epitope of MAb 710,
which inhibits the binding of vWF to glycoprotein lb (GPIb), was identified between
Ser 593 and Ser 678 on the tryptic 52/48 kDa fragment (aa 449-728) which contains
binding domains for GPIb, collagen, heparin, sulfatides and subendothclium extracellular
matrices. The epitope of MAb 723, which does not interfere with any known function
of vWF, was localized between Ser 523 and Gly 588. The epitopes of MAb 505 and MAb
400, which inhibit the binding of v WF to collagen, were identified between Leu 927
and Arg 1114 within the SPI fragment (aa 911-1365) corresponding to the central part
of the vWF subunit. The epitope of MAb 9, which inhibits the binding of vWF to GPIIb/IIIa,
was identified in the C-terminal part of the vWF subunit between Gin 1704 and Asp
1746, the latter being the third aa of the RGD sequence common to adhesive proteins
and serving as a recognition site for integrin receptors.