Mycoplasma pneumoniae (Mpn) is responsible for 15-20% of cases of community-acquired pneumonia. Up to 25% of infected patients develop extrapulmonary complications that can affect neurological, musculoskeletal, haematological and cardiovascular sites. Mpn is remarkable in that it produces an attachment organelle that directs how Mpn adheres to human respiratory epithelium by focusing several key adhesion molecules such as P1 and P30 to the tip. The P1 adhesin binds sialic acid moieties on surface of host cells. Notably, vaccines incorporating the P1 antigen have been problematic and currently there are no effective vaccines for Mpn.
Our surfaceome studies identify about 160 proteins on the cell surface of Mpn including a number that lack signal secretion sequences. One of these is elongation factor Tu (EfTu), a protein that moonlights on the surface of a number of Gram-positive and Gram-negative pathogens. Dallo et al., (20021) used immunogold EM microscopy to show the surface location of EfTu and described its ability to bind fibronectin (Fn). Subsequent studies identified two Fn binding motifs in EfTu (Balasubramanian et al., 20082, 20093). LC-MS/MS analysis of protein spots separated by 2D SDS-PAGE and SDS-PAGE of eluents from affinity column loaded with fetuin, actin, plasminogen, heparin and Fn as bait allowed us to map putative cleavage sites and identify cleavage fragments of EfTu that interact directly (or indirectly) with the bait proteins. Preliminary microscale thermophoresis experiments indicate that recombinant EfTu from Mpn binds heparin. Further experiments are underway to validate interactions between EfTu and other host molecules. EfTu is a multifunctional protein that is processed on the cell surface.