Mycoplasma pneumoniae (Mpn) is a major cause of community acquired pneumonia predominantly in children and the elderly. Mpn is remarkable in that it produces an attachment organelle that dictates how Mpn adheres to the human respiratory epithelium and the direction of motility. The attachment organelle focuses several key adhesion molecules to the tip of the organelle including the P1 and P30 adhesins. Three accessory proteins known as High Molecular Weight proteins HMW1, HMW2 and HMW3 as well as the product of the mpn142 gene are thought to play a significant role in localising the adhesins to the attachment organelle. At present there is no data to suggest that these accessory proteins have a direct role in adherence and their cellular location is still unresolved.

In this study we characterised the function of HMW1. HMW1 is 112 kDa protein that migrates abnormally during SDS-PAGE at approximately 250 kDa. Four recombinant fragments spanning HMW1 were constructed as polyhistidine fusion proteins, expressed in Escherichia coli and purified using nickel-affinity chromatography. Rabbit antisera were raised to each to these purified fragments and used to localise HMW1 in the attachment organelle by immunofluorescence microscopy. In preliminary experiments aimed at determining if HMW1 plays a role in binding host molecules, affinity chromatography columns separately loaded with feutin, actin, fibronectin, heparin or plasminogen were constructed. Binding interactions between these bait proteins and native Mpn proteins were identified by LC-MS/MS. Our data suggests that HMW1 contains binding domains for several of these host molecules. Specific binding affinity involving different regions of HMW1 and host molecules will be measured by thermophoresis.