Gene expression and characterization of a novel GH family 18 chitinase from extremely halophilic archaeon Halobacterium salinarum NRC-1

An open reading frame encoding a chitinase homolog (ChiN1) was found in the genome of extremely halophilic archaeon Halobacterium salinarum NRC-1. ChiN1 is a multidomain enzyme consisting of a chitin-binding domain, a polycystic kidney disease domain and a catalytic domain belonging to glycoside hydrolase family 18. chiN1 gene was successfully expressed in extremely halophilic archaeon Haloarcula japonica TR-1 by employing the promoter sequence of its cell surface glycoprotein gene. A large amount of recombinant ChiN1 was secreted into the culture supernatant. The Ha. japonica-produced ChiN1 was purified and characterized. The optimal pH and temperature of ChiN1 are pH 4.5 and 55°C, respectively. ChiN1 was most active at 1.0 M NaCl and stable over a wide range of NaCl concentration from 1.0 to 4.5 M. This is the first report on a chitinase from extremely halophilic archaeon.