Biochemical Characterization of a New β-Agarase from Cellulophaga algicola

Abstract

<i>Cellulophaga algicola</i> DSM 14237, isolated from the Eastern Antarctic coastal zone, was found to be able to hydrolyze several types of polysaccharide materials. In this study, a predicted β-agarase (<i>Ca</i>Aga1) from <i>C</i>. <i>algicola</i> was heterologously expressed in <i>Escherichia coli</i>. The purified recombinant <i>Ca</i>Aga1 showed specific activities of 29.39, 20.20, 14.12, and 8.99 U/mg toward agarose, pure agar, and crude agars from <i>Gracilaria lemaneiformis</i> and <i>Porphyra haitanensis</i>, respectively. <i>Ca</i>Aga1 exhibited an optimal temperature and pH of 40 ^oC and 7, respectively. <i>Ca</i>Aga1 was stable over a wide pH range from 4 to 11. The recombinant enzyme showed an unusual thermostability, that is, it was stable at temperature below or equal to 40^oC and around 70 ^oC, but was thermolabile at about 50 ^oC. With the agarose as the substrate, the <i>K</i>_m and <i>V</i>_max values for <i>Ca</i>Aga1 were 1.19 mg/mL and 36.21 U/mg, respectively. The reducing reagent (dithiothreitol) enhanced the activity of <i>Ca</i>Aga1 by more than one fold. In addition, <i>Ca</i>Aga1 was salt-tolerant given that it retained approximately 70% of the maximum activity in the presence of 2 M NaCl. The thin layer chromatography results indicated that <i>Ca</i>Aga1 is an endo-type β-agarase and efficiently hydrolyzed agarose into neoagarotetraose (NA4) and neoagarohexaose (NA6). A structural model of <i>Ca</i>Aga1 in complex with neoagarooctaose (NA8) was built by homology modeling and explained the hydrolysis pattern of <i>Ca</i>Aga1.