Structural explanation for allolactose (lac operon inducer) synthesis by lacZ β-galactosidase and the evolutionary relationship between allolactose synthesis and the lac repressor.

ABSTRACT: β-Galactosidase (lacZ) has bifunctional activity. It hydrolyzes lactose to galactose and glucose and catalyzes the intramolecular isomerization of lactose to allolactose, the lac operon inducer. β-Galactosidase promotes the isomerization by means of an acceptor site that binds glucose after its cleavage from lactose and thus delays its exit from the site. However, because of its relatively low affinity for glucose, details of this site have remained elusive. We present structural data mapping the glucose site based on a substituted enzyme (G794A-β-galactosidase) that traps allolactose. Various lines of evidence indicate that the glucose of the trapped allolactose is in the acceptor position. The evidence includes structures with Bis-Tris (2,2-bis(hydroxymethyl)-2,2',2″-nitrilotriethanol) a

SUBMITTER: Wheatley RW 

PROVIDER: S-EPMC3642343 | biostudies-literature | 2013 May

REPOSITORIES: biostudies-literature