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

alpha-L-Arabinofuranosidases I and II were purified from the culture filtra te of Streptomyces chartreusis GS901 and were found to have molecular masse s 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 t hat 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). Thi s enzyme cleaved the (1 --> 3) linkages of the arabinosyl side-chains of me thyl 3,5-di-O-alpha-L-arabino furanosyl alpha-L-arabinofuranoside in prefer ence to the (1 --> 5) linkages. alpha-L-Arabinofuranosidase I hydrolysed ap prox. 30% of the arabinan but hydrolysed hardly any linear arabinan. In con trast, alpha-L-Arabinofuranosidase II hydrolysed only (1 --> 5)-arabinofura nobioside among the regioisomeric methyl arabinobiosides and did not hydrol yse the arabinotrioside. Linear 1 --> 5-linked arabinan was a good substrat e for this enzyme, but it hydrolysed hardly any of the arabinan. Synergism between the two enzymes was observed in the conversion of arabinan and debr anched arabinan into arabinose. Complete amino acid sequencing of alpha-L-a rabinofuranosidase I indicated that the enzyme consists of a central cataly tic domain that belongs to family 51 of the glycoside hydrolases and additi onally that unknown functional domains exist in the N-terminal and C-termin al regions. The amino acid sequence of a-L-arabinofuranosidase II indicated that this enzyme belongs to family 43 of the glycoside hydrolase family an d, as this is the first report of an exo-1,5-alpha-L-arabinofuranosidase, i t represents a novel type of enzyme.