Sequence properties of the 1,2-diacylglycerol 3-glucosyltransferase from Acholeplasma laidlawaii membranes - Recognition of a large group of lipid glycosyltransferases in eubacteria and archaea

Synthesis of the nonbilayer-prone alpha -monoglucosyldiacylglycerol (MGlcDA G) is crucial for bilayer packing properties and the lipid surface charge d ensity in the membrane of Acholeplasma laidlawii. The gene for the responsi ble, membrane-bound glucosyltransferase (alMGS) (EC 2.4.1.157) was sequence d and functionally cloned in Escherichia coli, yielding MGlcDAG in the re c ombinants. Similar amino acid sequences were encoded in the genomes of seve ral Gram-positive bacteria (especially pathogens), thermophiles, archaea, a nd a few eukaryotes. Ah of these contained the typical EX7E catalytic motif of the CAZy family 4 of alpha -glycosyltransferases. The synthesis of MGlc DAG by a close sequence analog from Streptococcus pneumoniae (spMGS) was ve rified by polymerase chain reaction cloning, corroborating a connection bet ween sequence and functional similarity for these proteins. However, alMGS and spMGS varied in dependence on anionic phospholipid activators phosphati dylglycerol and cardiolipin, suggesting certain regulatory differences. Fol d predictions strongly indicated a similarity for alMGS land spMGS) with th e two-domain structure of the E. coli MurG cell envelope glycosyltransferas e and several amphipathic membrane binding segments in various proteins. On the basis of this structure, the alMGS sequence charge distribution, and a nionic phospholipid dependence, a model for the bilayer surface binding and activity is proposed for this regulatory enzyme.