2.A.50.2.1
The alanyl teichoic acid synthesis protein, DltB of 395 aas and 12 TMSs. It may transport activated alanine across the membrane (Perego et al., 1995).  Crystal structures of DltB, a membrane-bound O-acyl transferase, MBOAT, responsible for the D-alanylation of cell-wall teichoic acid in Gram-positive bacteri, both alone and in complex with the D-alanyl donor protein DltC (an acyl carrier protein) have been solved (Ma et al. 2018). DltB contains a ring of 11 peripheral transmembrane helices, which shield a highly conserved extracellular structural funnel extending into the middle of the lipid bilayer. The conserved catalytic histidine residue is located at the bottom of this funnel and is connected to the intracellular DltC (acyl carrier protein) through a narrow tunnel. Mutation of either the catalytic histidine or the DltC-binding site of DltB abolishes D-alanylation of lipoteichoic acid and sensitizes Bacillus subtilis to cell-wall stress, which suggests cross-membrane catalysis involving the tunnel. Structure-guided sequence comparisons among DltB and vertebrate MBOATs reveals a conserved structural core and suggests that MBOATs from different organisms have similar catalytic mechanisms (Ma et al. 2018).