Taxonomic distribution of proteins containing Bgal_small_N domains

The tree below includes only several representative species and genera. The complete taxonomic breakdown of all proteins containing Bgal_small_N domains can be accessed here. Click the counts or percentage values to display the corresponding proteins.

A structural view of the action of Escherichia coli (lacZ)beta-galactosidase.

Juers DH, Heightman TD, Vasella A, McCarter JD, Mackenzie L, Withers SG, Matthews BW
Biochemistry. 2001; 40: 14781-94

The structures of a series of complexes designed to mimic intermediatesalong the reaction coordinate for beta-galactosidase are presented. Thesecomplexes clarify and enhance previous proposals regarding the catalyticmechanism. The nucleophile, Glu537, is seen to covalently bind to thegalactosyl moiety. Of the two potential acids, Mg(2+) and Glu461, thelatter is in better position to directly assist in leaving groupdeparture, suggesting that the metal ion acts in a secondary role. Asodium ion plays a part in substrate binding by directly ligating thegalactosyl 6-hydroxyl. The proposed reaction coordinate involves themovement of the galactosyl moiety deep into the active site pocket. Forthose ligands that do bind deeply there is an associated conformationalchange in which residues within loop 794-804 move up to 10 A closer to thesite of binding. In some cases this can be inhibited by the binding ofadditional ligands. The resulting restricted access to the intermediatehelps to explain why allolactose, the natural inducer for the lac operon,is the preferred product of transglycosylation.