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Molecular characterization of the Mycoplasma gallisepticum pvpA gene which encodes a putative variable cytadhesin
S Boguslavsky1, D Menaker, I Lysnyansky
1Department of Membrane and Ultrastructure Research, The Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel.
Abstract:
A putative cytadhesin-related protein (PvpA) undergoing variation in its expression was identified in the avian pathogen Mycoplasma gallisepticum. The pvpA gene was cloned, expressed in Escherichia coli, and sequenced. It exhibits 54 and 52% homology with the P30 and P32 cytadhesin proteins of the human pathogens Mycoplasma pneumoniae and Mycoplasma genitalium, respectively. In addition, 50% homology was found with the MGC2 cytadhesin of M. gallisepticum and 49% homology was found with a stretch of 205 amino acids of the cytadherence accessory protein HMW3 of M. pneumoniae. The PvpA molecule possesses a proline-rich carboxy-terminal region (28%) containing two identical directly repeated sequences of 52 amino acids and a tetrapeptide motif (Pro-Arg-Pro-X) which is repeated 14 times. Genetic analysis of several clonal isolates representing different expression states of the PvpA product ruled out chromosomal rearrangement as the mechanism for PvpA phase variation. The molecular basis of PvpA variation was revealed in a short tract of repeated GAA codons, encoding five successive glutamate resides, located in the N-terminal region and subject to frequent mutation generating an in-frame UAA stop codon. Size variation of the PvpA protein was observed among M. gallisepticum strains, ranging from 48 to 55 kDa and caused by several types of deletions occurring at the PvpA C-terminal end and within the two directly repeated sequences. By immunoelectron microscopy, the PvpA protein was localized on the mycoplasma cell surface, in particular on the terminal tip structure. Collectively, these findings suggest that PvpA is a newly identified variable surface cytadhesin protein of M. gallisepticum.
Insights
A newly identified variable surface protein, PvpA, in Mycoplasma gallisepticum exhibits expression variation. This variation is due to mutations in a GAA codon repeat, affecting PvpA
Area of Science:
- Microbiology
- Molecular Biology
- Pathogen Research
Background:
- Mycoplasma gallisepticum is a significant avian pathogen.
- Cytadhesin proteins are crucial for mycoplasma adherence and pathogenicity.
- Phase variation in microbial surface proteins impacts host-pathogen interactions.
Purpose of the Study:
- To identify and characterize a novel cytadhesin-related protein (PvpA) in Mycoplasma gallisepticum.
- To elucidate the molecular mechanisms underlying PvpA expression and size variation.
- To determine the cellular localization of PvpA.
Main Methods:
- Cloning, expression in Escherichia coli, and sequencing of the pvpA gene.
- Homology analysis with known cytadhesin proteins.
- Genetic analysis of PvpA expression states and structural variations.
- Immunoelectron microscopy for protein localization.
Main Results:
- PvpA shows homology to cytadhesins from human and avian Mycoplasma species.
- PvpA variation is driven by mutations in a GAA codon repeat in the N-terminal region, leading to premature stop codons.
- Size variation (48-55 kDa) is caused by C-terminal deletions.
- PvpA localizes to the Mycoplasma gallisepticum cell surface, particularly the terminal tip.
Conclusions:
- PvpA is a novel, variable surface cytadhesin in Mycoplasma gallisepticum.
- The identified molecular mechanism explains PvpA phase variation.
- PvpA likely plays a role in M. gallisepticum adherence and pathogenesis.