Bacterial glycoglycerolipid synthases: Processive and non-processive glycosyltransferases in mycoplasma

Glycoglycerolipids are abundant membrane components in the photosynthetic tissues of plants and in cyanobacteria, with highly conserved structures (galactolipids). In non-photosynthetic bacteria, glycoglycerolipids are also widespread but with higher structural diversity. They are synthesized by the action of glycosyltransferases (GT), which transfers a glycosyl unit from a sugar nucleotide donor to diacylglycerol to form monoglycosyldiacylglycerol followed by a second transfer to give diglycosyldiacylglycerol. Both transferase activities are catalysed by different GT enzymes in plants, and many bacteria; however, processive enzymes, in which a single GT transfers the first and second (and eventually more) glycosyl units are also found in some bacteria. In this review, we summarize the diversity of glycosyltransferases involved in glycolipid biosynthesis in bacteria, focussing on mycoplasma enzymes and comparing processive and non-processive glycolipid synthases. Since glycoglycerolipids are key structural components of the plasma membrane in mycoplasmas, the glycolipid synthases involved in their biosynthesis are proposed as targets for the design of new antibiotics against mycoplasma infections.