A novel beta-agarase with high pH stability from marine Agarivorans sp. LQ48.
A novel endo-type beta-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 40 degrees C, the purified recombinant AgaA had a high specific activity of 349.3 micromol min(-1) mg(-1), a K(m) of 3.9 mg ml(-1), and a V(max) of 909.1 micromol min(-1) mg(-1) for agarose. The recombinant enzyme hydrolyzed the beta-1,4-glycosidic linkages of agarose, yielding neoagarotetraose and neoagarohexaose as the main products. Enzyme activity analysis revealed that the optimal temperature and pH of the recombinant AgaA were 40 degrees C and 7.0, respectively. Notably, AgaA still retained more than 95% activity after incubation at pH 3.0-11.0 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.
Long
Mengxian
M
State Key Laboratory of Agricultural Microbiology, Huazhong Agricultural University, Wuhan 430070, People's Republic of China.
Yu
Ziniu
Z
Xu
Xun
X
D000595:Amino Acid Sequence; D004795:Enzyme Stability; D020563:Gammaproteobacteria / Q000201:enzymology*; D006026:Glycoside Hydrolases / Q000737:chemistry* / Q000145:classification* / Q000378:metabolism; D008969:Molecular Sequence Data; D013379:Substrate Specificity
D006026:Glycoside Hydrolases; C019624:agarase