Isolation and characterization of an extracellular proteinase of Coccidioides immitis

A proteinase isolated from the respiratory pathogen, Coccidioides immitis, was shown to have collagenolytic and elastinolytic activity, as well as the ability to cleave human serum immunoglobulin G and secretory immunoglobulin A. Proteolytic activity was demonstrated with a bovine casein digestion assay in conidial culture exudates, mycelial and spherule culture filtrates, conidial and spherule wall material, and Sephacryl S-300 fractions of the isolated soluble conidial wall material described previously. One of the latter fractions (fraction 2) demonstrated high proteolytic activity. The proteinase was purified from this chromatographic fraction by cold acetone extraction followed by Sephadex G-50 gel filtration and was identified as a polypeptide band of 36,000 M(r) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. By means of tandem two-dimensional immunoelectrophoresis, the proteinase was identified as antigen 11 on the basis of its reaction in the coccidioidin/anticoccidioidin reference system. The proteinase is characterized by a broad substrate specificity, optimal activity at 35 to 40°C (pH 8.0) in the presence of human collagen, elastin, or hemoglobin, an isoelectric point of pH 4.5, and inhibition by organofluorides, N-tosyl-L-phenylalanine chloromethyl ketone, chymostatin, and α-1-antitrypsin. These features of the enzyme are comparable to those of chymotrypsinlike serine proteinases. Demonstration that the proteinase can cleave human immunoglobulins and digest ubiquitous tissue structural proteins (e.g., collagen and elastin) suggests that it may play a role in the virulence of the fungal pathogen.