Molecular Cloning, Structural Analysis, and Expression in Escherichia coli of a Chitinase Gene from

The gene chiA, which codes for endochitinase, was cloned from a soilborne Enterobacter agglomerans. Its com-plete sequence was determined, and the deduced amino acid sequence of the enzyme designated Chia_Entag yielded an open reading frame coding for 562 amino acids of a 61-kDa precursor protein with a putative leader peptide at its N terminus. The nucleotide and polypeptide sequences of Chia_Entag showed 86.8 and 87.7% identity with the corresponding gene and enzyme, Chia_Serma, of Serratia marcescens, respectively. Homology modeling of Chia_Entag’s three-dimensional structure demonstrated that most amino acid substitutions are at solvent-accessible sites. Escherichia coli JM109 carrying the E. agglomerans chiA gene produced and secreted Chia_Entag. The antifungal activity of the secreted endochitinase was demonstrated in vitro by inhibition of Fusarium oxysporum spore germination. The transformed strain inhibited Rhizoctonia solani growth on plates and the root rot disease caused by this fungus in cotton seedlings under greenhouse conditions. Many bacteria, fungi, and plants are able to hydrolyze chitin to oligomeric derivatives of N-acetyl-b-D-glucosamine (Glc-NAc), disaccharides, and GlcNAc monomer (15). The struc-tural genes encoding chitinases have been cloned from a wide variety of organisms, including bacteria (2, 8, 9, 17, 19, 20, 22)