Periodicity in Attachment Organelle Revealed by Electron Cryotomography Suggests Conformational Changes in Gliding Mechanism of Mycoplasma pneumoniae

Abstract

Mycoplasma pneumoniae, a pathogenic bacterium, glides on host surfaces using a unique mechanism. It forms an attachment organelle at a cell pole as a protrusion comprised of knoblike surface structures and an internal core. Here, we analyzed the three-dimensional structure of the organelle in detail by electron cryotomography. On the surface, knoblike particles formed a two-dimensional array, albeit with limited regularity. Analyses using a nonbinding mutant and an antibody showed that the knoblike particles correspond to a naplike structure that has been observed by negative-staining electron microscopy and is likely to be formed as a complex of P1 adhesin, the key protein for binding and gliding. The paired thin and thick plates feature a rigid hexagonal lattice and striations with highly variable repeat distances, respectively. The combination of variable and invariant structures in the internal core and the P1 adhesin array on the surface suggest a model in which axial extension and compression of the thick plate along a rigid thin plate is coupled with attachment to and detachment from the substrate during gliding.

Structural Study of MPN387, an Essential Protein for Gliding Motility of a Human-Pathogenic Bacterium, Mycoplasma pneumoniae

“…In the absence of HMW2, the force generated around the bowl complex may still be transmitted to the P1 adhesin much less efficiently than in the presence of HMW2, possibly through a distortion of the whole machinery. This hypothesis may also be supported by a recent observation based on electron cryotomography results showing that the flexible thick plate can move along the rigid thin plate (40). However, the consequence of the lack in MPN387 may not be simple, because the amounts of several component proteins of the attachment organelle were much reduced in the MPN387 mutant, although the strain retained the cytadherence activity (25).…”

“…The P1 adhesin complexes, somehow linked to the internal core, repeat a catch-pull-release cycle with sialylated oligosaccharides on the host surface. The organelle would then complete a gliding cycle by pulling forward the other parts of the cell connected to the back end of the bowl complex (22,40). The force generated in the bowl complex may be transmitted through MPN387 to the paired plates.…”

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

“…In contrast to M. pneumoniae, the M. penetrans AO consists solely of material whose lack of obvious organization is more reminiscent of the lucent area of M. pneumoniae than the core. Because both AOs, one with a core and one without, function in adherence and motility, it is possible that the core itself is dispensable for these functions in M. pneumoniae, as suggested previously (23,59), although this assertion is in opposition to some models (35,58). Therefore, we propose that the less organized material, constituting the ribosome-excluding zone in M. pneumoniae and perhaps the entire AO interior in M. penetrans, is the principal organizer of the AO, driving the concentration and organization of adhesins at the AO in both species and leaving motility to be carried out directly by adhesins with motor properties, as described for the more distantly related M. mobile (37).…”

“…The structure, which has been called the electron-dense core because of its prominent staining with metal-based dyes (56), has been the focus of considerable study (reviewed by Balish [2]). Because the ribosome-excluding zone is directly adjacent to the core, even in cells in which the core is detached from the membrane (35,57,58), it is likely formed by some fine substance linked to the core, probably regions of the same proteins that make up the core itself. Indeed, the failure to identify any non-core-associated proteins in the M. pneumoniae AO (58) supports this model.…”

Electron cryotomography of Mycoplasma pneumoniae mutants correlates terminal organelle architectural features and function

“…, white arrow), confirming previous observations from standard EMs of thin sections (Willby and Krause, ). Core duplication precedes cell division (Seto et al ., ; Hasselbring et al ., ), where wild‐type cores normally separate at the terminal button after duplication (Kawamoto et al ., ), by a process that likewise seems impaired in the absence of HMW3. Collectively these observations suggest a role in spatial organization for HMW3 in terminal organelle assembly and function.…”