Identification of variable regions (VR) within the ADAMTS13 MP domain. Amino acid sequence alignment of ADAMTS13 MP domain (residues 171-263) with other ADAMTS family MP domains. The active site HEXHXXXXXH sequence is labeled, and the perfectly conserved Met-turn methionine is indicated (arrowhead below alignment). Conserved (dark gray) and homologous (light gray) regions are highlighted; Cys residues are shown in black. Variable/nonconserved regions VR1, -2, -3, -3A, -3B, -3B(I), and -3B(II) are depicted by arrows.