Purification, characterization and gene cloning of two α-L-arabinofuranosidases from Streptomyces chartreusis GS901

alpha-L-Arabinofuranosidases I and II were purified from the culture filtrate of Streptomyces chartreusis GS901 and were found to have molecular masses of 80 and 37 kDa and pi values of 6.6 and 7.5 respectively. Both enzymes demonstrated slight reactivity towards arabinoxylan and arabinogalactan as substrates but did not hydrolyse gum arabic or arabinoxylo-oligosaccharides. alpha-L-Arabinofuranosidase I hydrolysed all of the alpha-linkage types that normally occur between two alpha-L-arabinofuranosyl residues, with the following decreasing order of reactivity being observed for the respective disaccharide linkages: alpha-(1 --> 2) alpha-(1 --> 3) alpha-(1 --> 5). This enzyme cleaved the (1 --> 3) linkages of the arabinosyl side-chains of methyl 3,5-di-O-alpha-L-arabino furanosyl alpha-L-arabinofuranoside in preference to the (1 --> 5) linkages. alpha-L-Arabinofuranosidase I hydrolysed approx. 30% of the arabinan but hydrolysed hardly any linear arabinan. In contrast, alpha-L-Arabinofuranosidase II hydrolysed only (1 --> 5)-arabinofuranobioside among the regioisomeric methyl arabinobiosides and did not hydrolyse the arabinotrioside. Linear 1 --> 5-linked arabinan was a good substrate for this enzyme, but it hydrolysed hardly any of the arabinan. Synergism between the two enzymes was observed in the conversion of arabinan and debranched arabinan into arabinose. Complete amino acid sequencing of alpha-L-arabinofuranosidase I indicated that the enzyme consists of a central catalytic domain that belongs to family 51 of the glycoside hydrolases and additionally that unknown functional domains exist in the N-terminal and C-terminal regions. The amino acid sequence of a-L-arabinofuranosidase II indicated that this enzyme belongs to family 43 of the glycoside hydrolase family and, as this is the first report of an exo-1,5-alpha-L-arabinofuranosidase, it represents a novel type of enzyme.