Purification and properties of ArfI, an alpha-L-arabinofuranosidase from Cytophaga xylanolytica.

Abstract

An alpha-L-arabinofuranosidase (alpha-L-arabinofuranoside arabinofuranohydrolase [EC 3.2.1.55]; referred to below as ArfI) from Cytophaga xylanolytica XM3 was purified 85-fold by anion-exchange and hydrophobic interaction column chromatography. The native enzyme had a pI of 6.1 and an apparent molecular mass of 160 to 210 kDa, and it appeared to be a trimer or tetramer consisting of 56-kDa subunits. With p-nitrophenyl-alpha-L-arabinofuranoside as the substrate, the enzyme exhibited a K(m) of 0.504 mM and a Vmax of 319 mumol.min-1.mg of protein-1, and it had optimum activity at pH 5.8 and 45 degrees C. ArfI was relatively stable over a pH range of 4 to 10 and at temperatures up to 45 degrees C, and it retained nearly full activity when stored at 4 degrees C for periods as long as 24 months. The enzyme also released arabinose from 4-methylumbelliferyl-alpha-L-arabinofuranoside, as well as from rye, wheat, corn cob, and oat spelt arabinoxylans and sugar beet arabinan, but not from arabinogalactan. ArfI showed no hydrolytic activity toward a range of p-nitrophenyl- or 4-methylumbelliferyl-glycosides other than arabinoside, for which it was entirely specific for the alpha-L-furanoside configuration. ArfI interacted synergistically with three partially purified endoxylanase fractions from C. xylanolytica in hydrolyzing rye arabinoxylan. However, cell fractionation studies revealed that ArfI was largely, if not entirely, cytoplasmic, so its activity in vivo is probably most relevant to hydrolysis of arabinose-containing oligosaccharides small enough to pass through the cytoplasmic membrane. Antibodies prepared against purified ArfI also cross-reacted with arabinofuranosidases from other freshwater and marine strains of C. xylanolytica, as well as with some proteins that did not possess arabinofuranosidase activity. To our knowledge, this is the first alpha-L-arabinofuranosidase to be purified and characterized from any gliding bacterium.