A novel type of subtilase from the psychrotolerant bacterium Pseudoalteromonas sp. SM9913: catalytic and structural properties of deseasin MCP-01

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Abstract
MCP-01, the main protease secreted by the deep-sea cold-adapted bacterium Pseudoalteromonas sp. SM9913, is a cold-adapted serine protease. Gene mcp01 encoding MCP-01 contains an ORF of 2508 bp encoding a protein of 835 amino acid residues with an M r of 87 773 Da, which is a multidomain subtilase precursor. Mature MCP-01 purified from the culture of strain SM9913 with an M r of 65.84 kDa is a multidomain protein composed of a catalytic domain, a linker, a P_proprotein domain and a polycystic kidney disease (PKD) domain. To the best of the authors' knowledge, no mature subtilase has been reported to date with this domain architecture. Phylogenetic analyses of subtilases showed that MCP-01 and 12 hypothetical proteins retrieved from public databases form a strongly supported group within the subtilase subfamily. These 13 proteins are predicted to share a similar domain architecture and represent a structurally novel group within the S8A subfamily. The substrate specificities of MCP-01 towards synthetic peptides differed from that of a typical S8A protease, subtilisin Carlsberg. Since most of this new subgroup of subtilases, including MCP-01 and the 12 MCP-01-like subtilases, are from deep-sea bacteria, they are termed deseasins. MCP-01 is the type example of a deseasin, since it is the only one that has been purified and characterized. In addition, the structural characteristics and catalytic properties of deseasin MCP-01 show that structurally and kinetically it is adapted to low temperatures.