FIG 1.

Model for the glycosylation process of type I LTA in L. monocytogenes and LTA production in the WT and a gtlA mutant strain. (A) Model for the glycosylation process of type I LTA. In this model, an enzyme with a cytoplasmically located glycosyltransferase (GT) domain, likely with a GT-A fold, utilizes UDP-Gal as the substrate to generate the C₅₅-P-Gal lipid intermediate (step 1). Following this, the lipid-linked sugar intermediate is transferred across the membrane, presumably with the aid of a dedicated lipid flippase (step 2), where a GT with an extracellular catalytic domain and likely assuming a GT-C fold links the sugar onto LTA (step 3). It is of note that none of the enzymes has as of yet been identified in L. monocytogenes or any other bacterium producing type I LTA. This figure was adapted from Percy et al. (15). (B) LTA detection by Western blotting. Extracts from strains 10403S (WT), 10403S/pPL3e (WT pPL3e), 10403S ΔgtlA (ΔgtlA), 10403S ΔgtlA/pPL3e (ΔgtlA pPL3e), and 10403S ΔgtlA/pPL3e-gtlA (ΔgtlA pPL3e-gtlA) were prepared and separated in 15% PAA gels as described in Materials and Methods. The LTA polymer was detected by Western blotting using a polyglycerol phosphate-specific monoclonal antibody; positions of protein standards (in kilodaltons) are indicated on the left-hand side. Three independent experiments were performed, and a representative result is shown.