A cold-active glucanase from the ruminal bacterium Fibrobacter succinogenes S85

We previously characterized two endoglucanases, CelG and EGD, from the meso philic ruminal anaerobe Fibrobacter succinogenes S85, Further comparative e xperiments have shown that CelG is a cold-active enzyme whose catalytic pro perties are superior to those of several other intensively studied cold-act ive enzymes. It has a lower temperature optimum, of 25 degrees C, and retai ns about 70% of its maximum activity at 0 degrees C, while EGD has a temper ature optimum of 35 degrees C and retains only about 18% of its maximal act ivity at 0 degrees C. When assayed at 4 degrees C, CelG exhibits a 33-fold- higher k(cat) value and a 73-fold-higher physiological efficiency (k(cat)/K -m) than EGD, CelG has a low thermal stability, as indicated by the effect of temperature on its activity and secondary structure. The presence of sma ll amino acids around the putative catalytic residues may add to the flexib ility of the enzyme, thereby increasing its activity at cold temperatures. Its activity is modulated by sodium chloride, with an increase of over 1.8- fold at an ionic strength of 0.03, Possible explanations for the presence o f a cold-active enzyme in a mesophile are that cold-active enzymes are more broadly distributed than previously expected, that lateral transfer of the gene from a psychrophile occurred, or that F. succinogenes originated from the marine environment.