Expression of Mycoplasma proteins carrying an affinity tag in M. pneumoniae allows rapid purification and circumvents problems related to the aberrant genetic code

Widespread ribosome stalling in a genome-reduced bacterium and the need for translational quality control

Trans-translation is a ubiquitous bacterial mechanism of ribosome rescue mediated by a transfer-messenger RNA (tmRNA) that adds a degradation tag to the truncated nascent polypeptide. Here, we characterize this quality control system in a genome-reduced bacterium, Mycoplasma pneumoniae (MPN), and perform a comparative analysis of protein quality control components in slow and fast-growing prokaryotes. We show in vivo that in MPN the sole quality control cytoplasmic protease (Lon) degrades efficiently tmRNA-tagged proteins. Analysis of tmRNA-mutants encoding a tag resistant to proteolysis reveals extensive tagging activity under normal growth. Unlike knockout strains, these mutants are viable demonstrating the requirement of tmRNA-mediated ribosome recycling. Chaperone and Lon steady-state levels maintain proteostasis in these mutants suggesting a model in which co-evolution of Lon and their substrates offer simple mechanisms of regulation without specialized degradation machineries. Finally, comparative analysis shows relative increase in Lon/Chaperone levels in slow-growing bacteria suggesting physiological adaptation to growth demand.

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Lon degrades efficiently tmRNA-tagged proteins in a genome-reduced bacterium

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tmRNA-tag mutants are viable and reveal extensive tagging activity in M. pneumoniae

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Co-evolution of Lon and their substrates offer simple mechanisms of regulation

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Chaperone and Lon relative levels correlate with bacterial growth rates

Mycoplasma pneumoniae, an underutilized model for bacterial cell biology

In recent decades, bacterial cell biology has seen great advances, and numerous model systems have been developed to study a wide variety of cellular processes, including cell division, motility, assembly of macromolecular structures, and biogenesis of cell polarity. Considerable attention has been given to these model organisms, which include Escherichia coli, Bacillus subtilis, Caulobacter crescentus, and Myxococcus xanthus. Studies of these processes in the pathogenic bacterium Mycoplasma pneumoniae and its close relatives have also been carried out on a smaller scale, but this work is often overlooked, in part due to this organism's reputation as minimalistic and simple. In this minireview, I discuss recent work on the role of the M. pneumoniae attachment organelle (AO), a structure required for adherence to host cells, in these processes. The AO is constructed from proteins that generally lack homology to those found in other organisms, and this construction occurs in coordination with cell cycle events. The proteins of the M. pneumoniae AO share compositional features with proteins with related roles in model organisms. Once constructed, the AO becomes activated for its role in a form of gliding motility whose underlying mechanism appears to be distinct from that of other gliding bacteria, including Mycoplasma mobile. Together with the FtsZ cytoskeletal protein, motility participates in the cell division process. My intention is to bring this deceptively complex organism into alignment with the better-known model systems.

Identification of an N-terminal 27 kDa fragment of Mycoplasma pneumoniae P116 protein as specific immunogen in M. pneumoniae infections

BACKGROUND

Mycoplasma pneumoniae is an important cause of respiratory tract infection and is increasingly being associated with other diseases such as asthma and extra-pulmonary complications. Considerable cross-reactivity is known to exist between the whole cell antigens used in the commercial serological testing assays. Identification of specific antigens is important to eliminate the risk of cross-reactions among different related organisms. Adherence of M. pneumoniae to human epithelial cells is mediated through a well defined apical organelle to which a number of proteins such as P1, P30, P116 and HMW1-3 have been localized, and are being investigated for adhesion, gliding and immunodiagnostic purposes.

METHODS

A 609 bp fragment P116(N-27), corresponding to the N-terminal region of M. pneumoniae P116 gene was cloned and expressed. A C-terminal fragment P1(C-40), of P1 protein of M. pneumoniae was also expressed. Three IgM ELISA assays based on P116(N-27), P1(C-40) and (P116 (N-27) + P1(C-40)) proteins were optimized and a detailed analysis comparing the reactivity of these proteins with a commercial kit was carried out. Comparative statistical analysis of these assays was performed with the SPSS version 15.0.

RESULTS

The expressed P116(N-27) protein was well recognized by the patient sera and was immunogenic in rabbit. P1(C-40) of M. pneumoniae was also immunogenic in rabbit. In comparison to the reference kit, which is reported to be 100% sensitive and 75% specific, ELISA assay based on purified P116(N-27), P1(C-40) and (P116(N-27) + P1(C-40)) proteins showed 90.3%, 87.1% and 96.8% sensitivity and 87.0%, 87.1% and 90.3% specificity respectively. The p value for all the three assays was found to be < 0.001, and there was a good correlation and association between them.

CONCLUSION

This study shows that an N-terminal fragment of P116 protein holds a promise for serodiagnosis of M. pneumoniae infection. The IgM ELISA assays based on the recombinant proteins seem to be suitable for the use in serodiagnosis of acute M. pneumoniae infections. The use of short recombinant fragments of P116 and P1 proteins as specific antigens may eliminate the risk of cross-reactions and help to develop a specific and sensitive immunodiagnostic assay for M. pneumoniae detection.