The IgA Protease of Clostridium ramosum

Publisher Summary This chapter elaborates the structural chemistry and the biological aspects of IgA protease of Clostridium ramosum. Bacterial IgA1 proteases are a group of endopeptidases with a remarkable specificity to cleave human IgAl molecules in the hinge region at a single Pro–Ser or Pro–Thr peptide bond. This unique microbial activity that separates the IgA1 molecule into intact Fab and Fc fragments was first identified in fluids of the human digestive tract, and subsequently isolated from Streptococcus sanguis. The enzyme was named IgA protease. C. ramosum IgA protease is highly specific. The enzyme is unable to cleave other human immunoglobulins. The amino acid sequence of the C. ramosum IgA protease deduced from the IgA gene revealed a translation product of 1234 amino acids. The first 30 residues constitute the signal peptide. In the C-terminus, a putative cell wall anchor was identified. The sequence SPQTG presumably constitutes the sortase recognition site. Other features including a small spacer, DNSN, separating the SPQTG motif from a transmembrane domain, IFLWFALLFSAAGVTGITAY, followed by a positively charged tail, NKKKKEHAE, at C-terminus. This strongly argues that the C. ramosum IgA protease is subject to sortase activity.