Molecular characterization of β-fructofuranosidases from Rhizopus delemar and Amylomyces rouxii.

Of the 19 strains of Rhizopus delemar deposited as Rhizopus oryzae, seven of them, NBRC 4726, NBRC 4734, NBRC 4746, NBRC 4754, NBRC 4773, NBRC 4775, and NBRC 4801, completely hydrolyzed exogenous sucrose and fructooligosaccharides. The sucrose-hydrolyzing enzyme was purified from the culture filtrate of R. delemar NBRC 4754 and classified to β-fructofuranosidase, similar to that of Amylomyces rouxii CBS 438.76. Fragments including β-fructofuranosidase genes (sucA) of seven strains of R. delemar and A. rouxii CBS 438.76 were amplified and sequenced by PCR with degenerated primers synthesized on the basis of the internal amino acid sequences of purified enzymes and successive inverse PCR. Nucleotide sequences of the obtained fragments revealed that open reading frames of 1,569 bp have no intron and encode 522 amino acids. The presumed proteins contained the typical domain of the glycoside hydrolase 32 family, including β-fructofuranosidase, inulinase, levanase, and fructosyltransferases. Amino acid sequences of SucA proteins from the seven strains of R. delemar were identical and showed 90.0 % identity with those of A. rouxii CBS 438.76. A dendrogram constructed from these amino acid sequences showed that SucA proteins are more closely related to yeast β-fructofuranosidases than to other fungal enzymes.