Identification of a Fungal Protein ofSyncephalastrum racemosumas Aspartic Proteinase

Abstract

During purification of fungal deoxyribonuclease (DNase) fromSyncephalastrum racemosum,a protein which was functionally unknown and persistently existed in the DNase-containing fractions through chromatography over DEAE-cellulose, hydroxylapatite, and phenyl-Sepharose was identified. The protein was finally separated from DNase after affinity chromatography on a cibacron blue-Sepharose column and purified to apparent homogeneity after gel chromatography on a Superdex 200 HR column. Ten tryptic peptides of this protein were isolated and sequenced. Searching in the sequence data bank with the aid of the computer program PC/Gene, we found that this protein was highly homologous to aspartic proteinases, such as pepsin and rhizopuspepsin. Because of its fungal origin and because the protein indeed showed catalytic cleavage on peptide bonds of bovine serum albumin, RNase, and carbonic anhydrase, we termed this protein syncephapepsin. The molecular weight of syncephapepsin is 38,000 daltons, based on gel filtration and sodium dodecyl sulfate–polyacrylamide electrophoresis.