A new neoagarobiose-producing agarase from Vibrio sp. LA1

Abstract

An agarolytic bacterium was isolated from the sea coast of Shantou in China and identified as Vibrio sp. LA1. The agarase gene agaA was cloned from Vibrio sp. LA1 by using degenerate oligonucleotide-primed PCR and genome walking technique. Gene agaA consists of a 2913 bp open reading frame encoding 970 amino acids; and the predicted molecular mass and isoelectric point were 108 kDa and 4.46, respectively. Based on the amino acid sequence similarity, the encoded protein (AgaA) of gene agaA should be an agarase of glycoside hydrolase family GH50 with a catalytic domain of glycoside hydrolase family GH42. Soluble expression of AgaA in Escherichia coli was obtained and investigated. The optimal temperature and pH for the activity of the purified recombinant agarase were 35°C and pH 6, respectively. The reducing reagent β-mercaptoethanol could increase the activity of agarase AgaA by more than 80%. AgaA showed exo-lytic activity on agarose degradation. It decomposed agarose to yield neoagarobiose as the sole product, which was different from the agarase Aga41A from Vibrio sp. CN41 that showed 95% identities of amino acid sequence to agarase AgaA. With single end product, purification procedure is easier than that with multi-products. Therefore, agarase AgaA could be a useful tool for producing the bioactive neoagarobiose.