The Variable Internal Structure of the Mycoplasma penetrans Attachment Organelle Revealed by Biochemical and Microscopic Analyses: Implications for Attachment Organelle Mechanism and Evolution

Abstract

Although mycoplasmas have small genomes, many of them, including the HIV-associated opportunist Mycoplasma penetrans, construct a polar attachment organelle (AO) that is used for both adherence to host cells and gliding motility. However, the irregular phylogenetic distribution of similar structures within the mycoplasmas, as well as compositional and ultrastructural differences among these AOs, suggests that AOs have arisen several times through convergent evolution. We investigated the ultrastructure and protein composition of the cytoskeleton-like material of the M. penetrans AO with several forms of microscopy and biochemical analysis, to determine whether the M. penetrans AO was constructed at the molecular level on principles similar to those of other mycoplasmas, such as Mycoplasma pneumoniae and Mycoplasma mobile. We found that the M. penetrans AO interior was generally dissimilar from that of other mycoplasmas, in that it exhibited considerable heterogeneity in size and shape, suggesting a gel-like nature. In contrast, several of the 12 potential protein components identified by mass spectrometry of M. penetrans detergent-insoluble proteins shared certain distinctive biochemical characteristics with M. pneumoniae AO proteins, although not with M. mobile proteins. We conclude that convergence between M. penetrans and M. pneumoniae AOs extends to the molecular level, leading to the possibility that the less organized material in both M. pneumoniae and M. penetrans is the substance principally responsible for the organization and function of the AO.IMPORTANCE Mycoplasma penetrans is a bacterium that infects HIV-positive patients and may contribute to the progression of AIDS. It attaches to host cells through a structure called an AO, but it is not clear how it builds this structure. Our research is significant not only because it identifies the novel protein components that make up the material within the AO that give it its structure but also because we find that the M. penetrans AO is organized unlike AOs from other mycoplasmas, suggesting that similar structures have evolved multiple times. From this work, we derive some basic principles by which mycoplasmas, and potentially all organisms, build structures at the subcellular level.KEYWORDS Mycoplasma, cytoskeleton, electron microscopy, evolution, fractionation, mass spectrometry, transcriptomics

Unpicking the mysterious symbiosis ofMycoplasmain salmonids

“…The majority of the variable surface antigenic molecules of mycoplasmas are lipoproteins (74)(75)(76), which, depending on the species, are encoded by single or multiple genes (64,77). The expression of these lipoproteins, due to extensive antigenic variation, is thought to be a major factor for immune evasion, for example the P35 lipoprotein and its paralogs, which are distributed across the surface of M. penetrans cells, are immunodominant (78)(79)(80). Two lipoprotein encoding genes were found only in Mycoplasma penetrans but not in the Mycoplasma's MAG in this study (Supp.…”

Virulence and molecular adaptation of human urogenital mycoplasmas: a review

“…The virulence genes are in fact specific for each species of Mycoplasma, forming their own category within the Mycoplasma genome [35]. It has, therefore, been speculated that the cytadherence tip organelle might indeed be a homoplasy resulting from evolutionary convergence [26]. This would explain the diversity in protein composition and structural arrangement (in the tip organelle) in different Mycoplasma species.…”

“…The binding component of this ABC transporter is OppA which is known to act as an adhesin in M. hominis. OppA has not been identified in M. penetrans and as such OppF might be serving as the adhesin involved in attachment [26]. Also present in the plasma membrane of M. penetrans is the highly abundant and immunogenic lipoprotein P35 [60,61].…”

“…Two paralogs of P35 and MYPE6960 (which has an ortholog MG_309 in M. genitalium that is known to bind and activate Toll-like receptors) have also been identified in the tip organelle. Five proteins of unknown molecular function that possess predicted alpha-helical coiled-coil regions with molecular weights greater than 90 kDa have also been reported to exist within the tip organelle [26]. These properties are typical of cytoskeletal proteins, hence, they may be playing a structural role in the formation of the cytadherence tip organelle of M. penetrans.…”

“…This glycolytic enzyme thus acts as an adhesin in some species of mycoplasmas [23]. Similarly, the multifunctional lipoprotein, oligopeptide permease substrate-binding protein (OppA) of M. hominis PG21 [24,25] and OppF of M. penetrans [26] are involved in cytadherence to host cells. The reliance on its host for essential nutrients, along with the utilisation of Figure 1.…”