THE PROLINE-RICH P65 PROTEIN OF MYCOPLASMA-PNEUMONIA IS A COMPONENT OF THE TRITON X-100-INSOLUBLE FRACTION AND EXHIBITS SIZE POLYMORPHISM IN THE STRAINS M129 AND FH

Previously, we described the identification of a novel Mycoplasma pneumoniae M129 protein, named P65 because of its apparent molecular mass of 65 kDa estimated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (T. Proft and R, Herrmann, Mel. Microbiol. 13:337-348, 1994). DNA sequence analysis of the P65 open reading frame (orfp65), however, revealed an ORF encoding a protein with a molecular weight of 47,034, This discrepancy can be explained by the unusual amino acid composition of this protein, According to the deduced amino acid sequence, the N-terminal half of P65 contains several penta- and hexapeptides (DPNAY and DPNQAY) forming a proline-rich acidic domain. Secondary-structure predictions indicated beta-sheets and turns within that region, suggesting an extended and rigid conformation. Near the C terminus of P65 the tripeptide Arg-Gly-Asp (RGD) was found, This motif is known to play an important role in binding of extracellular matrix proteins to integrins. P65 could be located exclusively to the Triton X-100-insoluble cell fraction, The results of immunofluorescence microscopy and of immunoadsorption experiments indicated that P65 carries surface-exposed regions. Mild treatment of whole cells with proteases resulted in cleavage of a limited amount of P65 molecules, suggesting either that only a small percentage of P65 molecules are exposed on the surface or that protease cleavage is hampered by a compact protein conformation or by binding of an unknown component to P65, P65 exhibits size polymorphism in Ill. pneumoniae M129 and FH. This is caused by an intragenetic duplication of a 54-bp sequence within the FH orfp65. As a consequence, the number of DPNAY pentapeptides increased from 9 to 12 repeats in the FH strain.