Isolation and characterization of two serine proteases from metagenomic libraries of the Gobi and Death Valley deserts

The screening of environmental DNA metagenome libraries for functional activities can provide an important source of new molecules and enzymes. In this study, we identified 17 potential protease-producing clones from two metagenomic libraries derived from samples of surface sand from the Gobi and Death Valley deserts. Two of the proteases, DV1 and M30, were purified and biochemically examined. These two proteases displayed a molecular mass of 41.5 kDa and 45.7 kDa, respectively, on SDS polyacrylamide gels. Alignments with known protease sequences showed less than 55% amino acid sequence identity. These two serine proteases appear to belong to the subtilisin (S8A) family and displayed several unique biochemical properties. Protease DV1 had an optimum pH of 8 and an optimal activity at 55A degrees C, while protease M30 had an optimum pH > 11 and optimal activity at 40A degrees C. The properties of these enzymes make them potentially useful for biotechnological applications and again demonstrate that metagenomic approaches can be useful, especially when coupled with the study of novel environments such as deserts.