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 pneu moniae M129 protein, named P65 because of its apparent molecular mass of 65 kDa estimated by sodium dodecyl sulfate polyacrylamide gel elect rophoresis (T. Proft and R, Herrmann, Mel. Microbiol. 13:337-348, 1994 ). DNA sequence analysis of the P65 open reading frame (orfp65), howev er, revealed an ORF encoding a protein with a molecular weight of 47,0 34, This discrepancy can be explained by the unusual amino acid compos ition of this protein, According to the deduced amino acid sequence, t he N-terminal half of P65 contains several penta- and hexapeptides (DP NAY and DPNQAY) forming a proline-rich acidic domain. Secondary-struct ure predictions indicated beta-sheets and turns within that region, su ggesting an extended and rigid conformation. Near the C terminus of P6 5 the tripeptide Arg-Gly-Asp (RGD) was found, This motif is known to p lay an important role in binding of extracellular matrix proteins to i ntegrins. P65 could be located exclusively to the Triton X-100-insolub le cell fraction, The results of immunofluorescence microscopy and of immunoadsorption experiments indicated that P65 carries surface-expose d regions. Mild treatment of whole cells with proteases resulted in cl eavage of a limited amount of P65 molecules, suggesting either that on ly a small percentage of P65 molecules are exposed on the surface or t hat protease cleavage is hampered by a compact protein conformation or by binding of an unknown component to P65, P65 exhibits size polymorp hism in Ill. pneumoniae M129 and FH. This is caused by an intragenetic duplication of a 54-bp sequence within the FH orfp65. As a consequenc e, the number of DPNAY pentapeptides increased from 9 to 12 repeats in the FH strain.