Biochemical and structural characterisation of MprF homologue, LpiA from Agrobacterium

Multiple peptide resistance factor (MprF) are bi-functional enzymes encoded by several bacterial species and carry out the transfer of an amino acid from a charged tRNA to the lipid head group and further translocate the lipid across the membrane. Biochemical studies have revealed that the soluble synthase domain generates specificity and the structures of MprF have defined the general architecture of these enzymes, and that they can exist in different oligomeric states. Here, we characterise the gene product of lpiA, a MprF homologue from Agrobacterium fabrum ( formerly called A. tumefaciens strain C58), a microbe that is commonly used in plant molecular biology. Cryo-EM analysis of AfMprF reveals a dimeric structure both in detergent micelle and in lipid nanodisc, and similar in architecture to the homologous enzyme from related Rhizobium sp. We further analyse some conserved residues in the soluble domain and suggest that the sulphur-aromatic motifs play a key role in substrate binding. Similar architecture of enzymes in closely related bacterial species of Agrobacterium and Rhizobium hints an evolutionary relationship but the importance of these oligomeric states in vivo remains to be analysed.