Stability, interdependence, and fibronectin-binding capabilities of the putative cytoskeletal proteins of Mycoplasma gallisepticum

Date of Completion

January 2006


Biology, Microbiology




The avian pathogen Mycoplasma gallisepticum is known to attach to epithelia using the attachment organelle. The assembly of the attachment organelle for the closely related human pathogen Mycoplasma pneumoniae and the hierarchal stability of its components have been described previously by Balisli & Krause. Scanning electron microscopy indicates that the low passage variant of the pathogenic M. gallisepticum Strain R (Rlow) and its attenuated, high passage derivative (Rhigh) produce a short, broad-based attachment organelle that differs in shape from that of M. pneumoniae. Examination of the M. gallisepticum homologues of the attachment organelle components of M. pneumoniae as they exist in Rlow and Rhigh revealed changes in gene size and in some cases genomic organization. In addition, the hierarchy of stability described for M. pneumoniae appears markedly different from that observed for M. gallisepticum. The work presented describes features of the attachment organelle proteins, including the previously characterized GapA, CrmA, and MGC2, as well as the newly designated Hlp1, Hlp2, Hlp3, and PlpA, with regard to their interdependence, hierarchal stability, co-transcription, and impact on attachment organelle formation. In addition to being the homologues of M. pneumoniae cytoskeletal proteins, PlpA and Hlp3 were found to confer upon virulent Mycoplasma gallisepticum strain Rlow the ability to bind the extracellular matrix protein fibronectin. Rhigh, which was found to lack PlpA, was deficient in this ability. A twenty-amino acid region of PlpA was demonstrated to bind the gelatin/heparin-binding domain of fibronectin, and represents a novel binding mechanism. PlpA, consistent with its M. pneumoniae counterpart, was demonstrated to be a surface-exposed, integral membrane protein despite a lack of classical membrane-spanning domains. Short, hydrophobic peptides from predicted low-complexity regions of PlpA were shown to embed within liposomes and mycoplasmal membranes, indicating that these regions may function as atypical transmembrane domains. The data presented represent the first description of the M. gallisepticum homologues of the cytoskeletal proteins of M. pneumoniae. Despite sequence homology and similarities in chemical properties for each set of proteins, their function and roles in virulence appear to be distinct in M. gallisepticum and M. pneumoniae. ^