The structure of the OmpA/Pal protein of Anaplasma phagocytophilum

Peptidoglycan associated lipoprotein (Pal) and Outer Membrane Protein A (OmpA), interact with the outer membrane and peptidoglycan in Gram-negative bacteria, conferring structural integrity to the bacterial cell and functioning in cell division. Both OmpA and Pal proteins have moonlighting roles as virulence factors, facilitating infection and host-pathogen interactions in a range of bacteria. The OmpA-like protein of Anaplasma phagocytophilum, a tick-borne pathogen that infects a wide range of hosts, seems to function primarily as a virulence factor, since this bacterium lacks a peptidoglycan cell wall. Here we present crystal structures of the OmpA-like protein of A. phagocytophilum, demonstrating that this protein has amino acid insertions that confer flexibility. This insertion is also found in the OmpA-like proteins of other pathogens, related to A. phagocytophilum. Whether this flexibility is reflective of any adaptations for host-pathogen interactions remains to be determined but, since the OmpA-like proteins of Anaplasma species are current targets for vaccine development, might have importance for these efforts.