biostudies-literatureJuers DHHoward Hughes Medical InstituteNIGMS NIH HHS1281-92https://www.ebi.ac.uk/biostudies/studies/S-EPMC2774438biostudies-literatureUnknown18(6)The active site of ss-galactosidase (E. coli) contains a Mg(2+) ion ligated by Glu-416, His-418 and Glu-461 plus three water molecules. A Na(+) ion binds nearby. To better understand the role of the active site Mg(2+) and its ligands, His-418 was substituted with Asn, Glu and Phe. The Asn-418 and Glu-418 variants could be crystallized and the structures were shown to be very similar to native enzyme. The Glu-418 variant showed increased mobility of some residues in the active site, which explains why the substitutions at the Mg(2+) site also reduce Na(+) binding affinity. The Phe variant had reduced stability, bound Mg(2+) weakly and could not be crystallized. All three variants have low catalytic activity due to large decreases in the degalactosylation rate. Large decreases in substrate bProtein science : a publication of the Protein SocietyDirect and indirect roles of His-418 in metal binding and in the activity of beta-galactosidase (E. coli).PMC2774438GM 20066Rob BMatthews BWDugdale MLRahimzadeh NLee MGiang CJuers DHHuber REfalseDirect and indirect roles of His-418 in metal binding and in the activity of beta-galactosidase (E. coli).The active site of ss-galactosidase (E. coli) contains a Mg(2+) ion ligated by Glu-416, His-418 and Glu-461 plus three water molecules. A Na(+) ion binds nearby. To better understand the role of the active site Mg(2+) and its ligands, His-418 was substituted with Asn, Glu and Phe. The Asn-418 and Glu-418 variants could be crystallized and the structures were shown to be very similar to native enzyme. The Glu-418 variant showed increased mobility of some residues in the active site, which explains why the substitutions at the Mg(2+) site also reduce Na(+) binding affinity. The Phe variant had reduced stability, bound Mg(2+) weakly and could not be crystallized. All three variants have low catalytic activity due to large decreases in the degalactosylation rate. Large decreases in substrate b2009-01-01T00:00:00Z2009 Jun2025-04-19T23:53:19.738Z2019-03-27T00:26:25ZS-EPMC27744381947241310.1002/pro.140