Figure 1

DNA sequence of chromosomal region encoding chitosanase Cho4239-1 and deduced amino acid sequence. Nucleotide numbers and amino acid numbers are indicated, omitting the first 24 amino acid residues suggested to function as a signal peptide. The translation initiation codon (ATG) and the stop codon (TAA) of the open reading frame are shown in bold. A predicted signal peptidase II recognition sequence is underlined, and a vertical arrow indicates the putative signal peptide cleavage site. An alternative ATG initiation codon and the corresponding signal peptidase I recognition sequence and cleavage site is underlined with gray. Amino acid residues believed to have significant function in substrate binding, catalysis and structural conformation are shown in bold. Substrate binding subsites B (Pro₁₇₉), C (Gly₇₇;Asp₈₄), D (Ile₇₆;Glu₂₂₆) and E (Tyr₆₂) are conserved among chitosanases with residues in subsites C and E as characteristics of glycosyl hydrolase family 46. Also the catalytic glutamic acid (Glu₅₀) is conserved but the corresponding aspartic acid which is conserved among other chitosanases could not be identified here. The alternative active site residues (Glu₆₄ and Thr₇₂; [29]) are indicated in bold. Protein stabilizing residues identified in other chitosanases were also found to be conserved here (Trp₅₆;Trp₁₂₈;Arg₂₃₅;Trp₂₅₇) [12, 13].