The active site regions of lacZ and ebg beta-galactosidases are homologous.
1983; Elsevier BV; Volume: 258; Issue: 17 Linguagem: Inglês
10.1016/s0021-9258(17)44440-1
ISSN1083-351X
AutoresAudrée V. Fowler, Peter J. Smith,
Tópico(s)Glycosylation and Glycoproteins Research
Resumoto alkylate methionine 502 in lac2 &galactosidase, was used to label the second naturally occurring &galactosidase of Escherichia coli (ebg').The reagent was also used to label two mutant forms of the enzyme (ebg" and ebgb) selected for enhanced lactase activity.In the case of ebg' and ebga, 75 and 85% of the label, respectively, was incorporated into a tryptic peptide which is homologous (38% identity) to residues 483-503 of the lac2 &galactosidase sequence.In the ebg' and ebg" enzymes, a serine probably is alkylated.In the case of the ebgb enzyme, 61% of the label is found on a tryptic peptide homologous (69% identity) with residues 457-468 of the lac2 &galactosidase.In this peptide, a glutamic acid and a tyrosine residue are both alkylated.Escherichia coli cells normally cannot grow on lactose when the lac2 gene, which codes for @-D-galactosidase (EC 3.2.1.23),is deleted.Cells with lucZ deletions selected for growth on lactose were found to have produced a new @-galactosidase.The name ebg' has been coined for this enzyme (1, a), that is, evolved @-galactosidase.The ebg gene maps at 66 min on the E. coli chromosome whereas lac2 maps at 8 min (3).The ebg enzyme has a subunit molecular weight of 120,000 (4), very close to that of the lucZ enzyme.However, the active ebg protein is a hexamer not a tetramer (4), and the two proteins do not cross-react with antisera prepared against each type of protein (5).Since it has been so central to studies of molecular biology,
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