Purification and characterization of extracellular alkaline serine protease from Stenotrophomonas maltophilia strain S-1

Abstract

The present study was conducted by screening soil bacteria in an attempt to isolate a bacterium that produced extracellular alkaline protease, and for purification and characterization of the protease. Soil bacteria were screened by growth on casein as the sole carbon source. Characterization of a strain isolated from soil of Abashiri, Japan indicated a taxonomic affiliation to Stenotrophomonas maltophilia, and was named S-1 strain. The purified S-1 protease, designed S. maltophilia Protease-1 (SmP-1), exhibited an optimal pH of 12.0, optimal reaction temperature of 50 degrees C and a molecular mass of approximately 40 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The cleavage sites of the oxidized-insulin B chain by SmP-1 were identified as Leu6-Cys7, Cys7-Gly8, Tyr16-Leu17 and Leu17-Val18. The N-terminal amino acid sequence of the purified alkaline protease was determined as NH2-SASAPMVSGVAALVLE. A novel extracellular alkaline serine protease was isolated from S. maltophilia strain S-1. The optimal pH of the proteolytic activity was pH 12.0. The extremely high optimal pH and heat stability of the alkaline serine protease SmP-1 might make it widely applicable to food and other industries.