Molecular cloning and purification of an endochitinase from Serratia marcescens (Nima)

An endochitinase gene from the Serratia marcescens Nima strain (chiA Nima) was cloned, sequenced, and expressed in Escherichia coli DH5alphaF', and the recombinant protein (ChiA Nima) was purified by hydrophobic interaction chromatography. chiA Nima contains an open reading frame (ORF) that encodes an endochitinase with a deduced molecular weight and an isoelectric point of 61 kDa and 6.84, respectively. A sequence at the 5'-end was identified as a signal peptide, recognized by Gram-negative bacteria transport mechanism. Comparison of ChiA Nima with other chitinases revealed a modular structure formed by the catalytic domain and a putative chitin-binding domain. The purified chitinase was able to hydrolyze both trimeric and tetrameric fluorogenic substrates, but not a chitobiose analog substrate. ChiA Nima showed high enzymatic activity within a broad pH range (pH 4.0-10.0), with a peak activity at pH 5.5. The optimal temperature for enzymatic activity was detected at 55 degrees C.