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Mar Biotechnol (2010) 12:6269 DOI 10.1007/s10126-009-9200-7
ORIGINAL ARTICLE
A Novel -Agarase with High pH Stability from Marine Agarivorans sp. LQ48
Mengxian Long & Ziniu Yu & Xun Xu
Received: 20 January 2009 /Accepted: 19 May 2009 /Published online: 30 May 2009 # Springer Science + Business Media, LLC 2009
Abstract A novel endo-type -agarase gene, agaA, was cloned from a newly isolated marine bacterium, Agarivorans sp. LQ48. It encodes a protein of 457 amino acids with a calculated molecular mass of 51.2 kDa. The deduced protein contains a typical N-terminal signal peptide of 25 amino acid residues, followed by a catalytic module, which is homologous to that of glycoside hydrolase family 16. A sequence similar to a carbohydrate-binding module is found in the C-terminal region of the enzyme. The overall amino acid sequence shares a highest identity of 73% with the sequence of beta-agarase AgaB from Pseudoalteromonas sp. strain CY24. The mature agarase was highly expressed extracellularly in Escherichia coli. At pH 7.0 and 40C, the purified recombinant AgaA had a high specific activity of 349.3 mol min1 mg1, a Km of 3.9 mg ml1, and a Vmax of 909.1 mol min1 mg1 for agarose. The recombinant enzyme hydrolyzed the -1,4-glycosidic linkages of aga-rose, yielding neoagarotetraose and neoagarohexaose as the main products. Enzyme activity analysis revealed that the optimal temperature and pH of the recombinant AgaA were 40C and 7.0, respectively. Notably, AgaA still retained more than 95% activity after incubation at pH 3.011.0 for 1 h, a characteristic much different from other agarases reported. It is the first agarase identified to have so wide a pH range stability. This favorable property could make
AgaA to be attractive to the food, cosmetic, and medical industrial applications.
Keywords -Agarase . Agarivorans sp. . Characterization . pH stability. GH16
Introduction
Agar, as a usual gelling substance in scientific research and as an ingredient in the food industry, is found in the cell wall of marine red algae and consists of two different components of agarose and agaropectin (Araki 1937). Agarose is a linear polysaccharide composed of alternating residues of 3-O-linked -D-galactopyranose and 4-O-linked 3,6-anhydro--L-galactopyranose (Hamer et al. 1977). Neoagarooligosaccharides, the agarase- hydrolization product from agar or agarose, possess diverse biological functions and have many potential applications in...