Digestive beta-glucosidases from the wood-feeding higher termite, Nasutitermes takasagoensis: intestinal distribution, molecular characterization, and alteration in sites of expression.
beta-Glucosidase [EC 3.2.1.21] hydrolyzes cellobiose or cello-oligosaccharides into glucose during cellulose digestion in termites. SDS-PAGE and zymogram analyses of the digestive system in the higher termite Nasutitermes takasagoensis revealed that beta-glucosidase activity is localized in the salivary glands and midgut as dimeric glycoproteins. Degenerate PCR using primers based on the N-terminal amino acid sequences of the salivary beta-glucosidase resulted in cDNA fragments of 1.7 kb, encoding 489 amino acids with a sequence similar to glycosyl hydrolase family 1. Moreover, these primers amplified cDNA fragments from the midgut, and the deduced amino acid sequences are 87-91% identical to those of the salivary beta-glucosidases. Successful expression of the cDNAs in Escherichia coli implies that these sequences also encode functional beta-glucosidases. These results indicate that beta-glucosidases that primarily contribute to the digestive process of N. takasagoensis are produced in the midgut. Reverse transcription-PCR analysis indicated the site-specific expression of beta-glucosidase mRNAs in the salivary glands and midgut. These results suggest that termites have developed the ability to produce beta-glucosidases in the midgut, as is the case for endo-beta-1,4-glucanase, in which the site of expression has shifted from the salivary glands of lower termites to the midgut of higher termites.
Tokuda
Gaku
G
Tropical Biosphere Research Center, COMB, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan. tokuda@comb.u-ryukyu.ac.jp
Miyagi
Mio
M
Makiya
Hiromi
H
Watanabe
Hirofumi
H
Arakawa
Gaku
G
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D044602:Cellulases / Q000235:genetics / Q000378:metabolism*; D005247:Feeding Behavior; D041981:Gastrointestinal Tract / Q000201:enzymology; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D020049:Isoptera / Q000201:enzymology*; D008969:Molecular Sequence Data; D014934:Wood
D044602:Cellulases