Location of MBL-associated serine proteases binding motifs on human mannan-binding lectin (MBL)

The lectin pathway provides an antibody independent route of complement activation. Mannan-binding lectin (MBL) can form compound with MBL-associated serine proteases (MASPs) through its collagen-like region (CLR) to initiate complement fixation. In this study, we designed and synthesized a range of peptides according to the sequence of CLR in human MBL, which were assumed to block the MBL-MASP interaction, in order to locate the serine protease binding motifs on human MBL. It was demonstrated that MASPs bind on the C-terminal side of the hinge region formed by an interruption in the Gly-X-Y repeat pattern of the collagen-like domain. In addition, Arg32Cys, Gly35Asp and Gly37Glu mutant proteins have the similar serine protease binding characteristic with wild type MBL, but the binding between mutated MBL proteins and MASPs is much weaker than that between wild type MBL protein and MASPs.