Cloning and sequence analysis of Vibrio halioticoli genes encoding three types of polyguluronate lyase

The alginate lyase-coding genes of Vibrio halioticoli IAM 14596(T), which w as isolated from the gut of the abalone Haliotis discus hannai, were cloned using plasmid vector pUC 18, and expressed in Escherichia coli. Three algi nate lyase-positive clones, pVHB, pVHC, and pVHE, were obtained, and all cl ones expressed the enzyme activity specific for polyguluronate. Three genes , alyVG1, alyVG2, and alyVG3, encoding polyguluronate lyase were sequenced: alyVG1 from pVHB was composed of a 1056-bp open reading frame (ORF) encodi ng 352 amino acid residues; alyVG2 gene from pVHC was composed of a 993-bp ORF encoding 331 amino acid residues; and alyVG3 gene from pVHE was compose d of a 705-bp ORF encoding 235 amino acid residues. Comparison of nucleotid e and deduced amino acid sequences among AlyVG1, AlyVG2, and AlyVG3 reveale d low homologies. The identity value between AlyVG1 and AlyVG2 was 18.7%, a nd that between AlyVG2 and AlyVG3 was 17.0%. A higher identity value (26.0% ) was observed between AlyVG1 and AlyVG3. Sequence comparison among known p olyguluronate lyases including AlyVG1, AlyVG2, and AlyVG3 also did not reve al an identical region in these sequences. However, AlyVG1 showed the highe st identity value (36.2%) and the highest similarity (73.3%) to AlyA from K lebsiella pneumoniae. A consensus region comprising nine amino acid (YFKAGX YXQ) in the carboxy-terminal region previously reported by Mallisard and co lleagues was observed only in AlyVG1 and AlyVG2.