Purification and characterization of an immunoglobulin A1 protease from Bacteroides melaninogenicus

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Abstract
Attention has recently been focused on bacterial proteases with the capacity to cleave IgA (IgA proteases) as possible pathogenic factors in bacterial meningitis, gonorrhoea and destructive peridontal disease. A method for the rapid purification of a specific IgA1 protease from B. melaninogenicus is described. The IgA1 protease was purified 6172-fold with a yield of 9% by (NH4)2SO4 precipitation, DEAE-ion exchange chromatography and separation on a preparative TSK-G 3000SWG high-pressure gel permeation chromatography column. The enzyme was specific for human IgA1 and cleaved a prolyl-seryl peptide bond in the hinge region of the .alpha.1 chain between residues 223 and 224. The MW of the enzyme was 62,000, the isoelectric point was 5.0 and the Km was 3.4 .times. 106. The enzyme was active over a broad pH range and had maximal activity at pH 5.0. B. melaninogenicus IgA1 protease was classified as a thiol protease on the basis of its inhibition by traditional protease inhibitors and the fact that it was active only under reducing conditions.