Fluorogenic substrates and ADAMTS13 constructs. (A) Substrates prepared from species-specific VWF sequences. The arrowhead marks the Tyr-Met bond (Armadillo, Tyr-Leu) cleaved by ADAMTS13. The N-terminus is modified with IRDye QC-1 (QC1), and the indicated Cys residue is modified with DyLight 633 (DyL). Segments of the sequence that make extensive contacts with MDTCS domains are indicated. Residues in red indicate differences from the human sequence. (B) Recombinant human ADAMTS13 and variants. Except for MDTCS, all constructs have an N-terminal StrepTag II (st) and enteropeptidase cleavage site.