A novel beta-galactosidase gene isolated from the bacterium Xanthomonas manihotis exhibits strong homology to several eukaryotic beta-galactosidases.
The gene encoding a beta-galactosidase from Xanthomonas manihotis was cloned into Escherichia coli. The gene resides on a 2.4 kb DNA fragment which was isolated from a partial Sau3A library in the cloning vector pUC19 using 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-gal) as the selection. The enzyme produced by the clone has a specificity for beta 1-3- > beta 1-4-linked galactose. The nucleotide sequence of the gene was determined. The deduced protein sequence contained 597 amino acids yielding a monomeric molecular mass of 66 kDa. The cloned beta-galactosidase showed no similarity to any known prokaryotic beta-galactosidase. However, extensive similarity was observed with eukaryotic beta-galactosidases from animals, plants and fungi. The strongest similarity was with the beta-galactosidases found in the human and mouse lysosomes (42 and 41% identity, respectively). Alignment of the X.manihotis and eukaryotic beta-galactosidase sequences revealed seven highly conserved domains common to each protein. Additionally, Domain 1 in X.manihotis showed similarity to regions within catalytic domains from seven xylanases and cellulases belonging to family 10 of glucosyl hydrolases. A region spanning Domain 2 showed similarity to the catalytic domain of endo beta 1-3 glucanases from tobacco and barley.
Taron
C H
CH
New England Biolabs Inc., Beverly, MA 01915, USA.
Benner
J S
JS
Hornstra
L J
LJ
Guthrie
E P
EP
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D004269:DNA, Bacterial; D004926:Escherichia coli / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid; D014974:Xanthomonas / Q000201:enzymology / Q000235:genetics*; D001616:beta-Galactosidase / Q000235:genetics* / Q000378:metabolism
D004269:DNA, Bacterial; D001616:beta-Galactosidase