The adhesin related 30-kDa protein of Mycoplasma pneumoniae exhibits size and antigen variability.

Mycoplasma pneumoniae is a pathogenic bacterium colonizing epithelial cells of the human respirator tract. Using an erythrocyte binding assay we isolated a cytadsorption negative mutant designated M7 which has lost 12 of a total of 13 repetitive sequences of a proline rich C-terminal region of the adhesin related 30-kDa protein. The truncated adhesin related protein of 22 kDa showed reduced antigenicity compared to the corresponding wild-type protein. Moreover, the mutant M7 proved incapable of adhering to erythrocytes and to a human colon carcinoma cell line indicating that the repetitive C-terminal region of the 30-kDa protein is essential for effective cytadherence. The adhesin related 30-kDa protein as well as the truncated forms of the corresponding protein were accessible to carboxypeptidase Y which clearly shows surface exposure of the C-terminus of this protein.