Characterization of an endo-processive-type xyloglucanase having a β-1, 4-glucan-binding module and an endo-type xyloglucanase from Streptomyces avermitilis

摘要

We cloned two glycoside hydrolase family 74 genes, the sav_1856 gene and the sav_2574 gene, from streptomyces avermitilis nbrc14893 and characterized the resultant recombinant proteins.The sav_1856 gene product(saGH74a) consisted of a catalytic domain and a family 2 carbohydrate-binding module at the c terminus, while the sav_2574 gene product(sagh74b) consisted of only a catalytic domain.Sagh74a and sagh74b were expressed successfully and had molecular masses of 92 and 78 kda, respectively.Both recombinant proteins were xyloglucanases.SaGH74a had optimal activity at 60°c and ph 5.5, while sagh74b had optimal activity at 55°c and ph 6.0.SaGH74a was stable over a broad ph range(pH 4.5 to 9.0), whereas sagh74b was stable over a relatively narrow ph range(pH 6.0 to 6.5).Analysis of the hydrolysis products of tamarind xyloglucan and xyloglucan-derived oligosaccharides indicated that sagh74a was endo-processive, while sagh74b was a typical endo-enzyme.The c terminus of sagh74a, which was annotated as a carbohydrate-binding module, bound to β-1, 4-linked glucan-containing soluble polysaccharides such as hydroxyethyl cellulose, barley glucan, and xyloglucan.