Functional role of Y1544 in A2 domain stability and ADAMTS13 interaction. VWF A2 variants Y1544A, Y1544A/N1574Q (A), Y1544D, Y1544D/N1574Q (B), and Y1544R and Y1544R/N1574Q (C) were subjected to DSF assay in the presence of 1 mM EDTA or 5 mM CaCl₂. Unfolding curves were compared with WT VWF A2 alone (A-C, gray lines). (D-E) The solution competition binding of the above VWF A2 domain variants (Y1544A or Y1544A/N1574Q, circles; Y1544D or Y1544D/N1574Q, squares; Y1544R or Y1544R/N1574Q, triangles) were compared with WT (D, gray lines) and N1574Q (E, gray lines). Results are means ± SEM of at least 3 independent experiments.