Figure 2.

Cofactor assay of seven FH1-4 mutants. Disappearance of the α^′-chain of C3b, and appearance of 43- and 68-kDa FI/FH-generated proteolytic products of the α^′-chain of iC3b, were observed in Coomassie-stained gels following SDS-PAGE. Single-cysteine substitution FH1-4 mutants, as indicated, were labeled with Ax555 maleimide then samples incubated with FI and C3b (10 min, 37°C) prior to loading. Plasma-purified full-length FH or recombinant FH1-4 served as positive controls (+ve); PBS-only as a negative control (−ve). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]