Alternative conformation of the C-domain of the P140 protein from Mycoplasma genitalium

Abstract

The human pathogen Mycoplasma genitalium is responsible for urethritis in men, and for cervicitis and pelvic inflammatory disease in women. The adherence of M. genitalium to host target epithelial cells is mediated through an adhesion complex called Nap, which is essential for infectivity. Nap is a transmembrane dimer of heterodimers of the immunodominant proteins P110 and P140. The M. genitalium genome contains multiple copies of portions that share homology with the extracellular regions of P140 and P110 encoded by the genes mg191 and mg192, respectively. Homologous recombination between the genes and the copies allows the generation of a large diversity of P140 and P110 variants to overcome surveillance by the host immune system. Interestingly, the C-terminal domain (C-domain) of the extracellular region of P140, which is essential for the function of Nap by acting as a flexible stalk anchoring the protein to the mycoplasma membrane, presents a low degree of sequence variability. In the present work, the X-ray crystal structures of two crystal forms of a construct of the P140 C-domain are reported. In both crystal forms, the construct forms a compact octamer with D4 point-group symmetry. The structure of the C-domain determined in this work presents significant differences with respect to the structure of the C-domain found recently in intact P140. The structural plasticity of the C-domain appears to be a possible mechanism that may help in the functioning of the mycoplasma adhesion complex.

Pathogenicity and virulence of Mycoplasma genitalium: Unraveling Ariadne’s Thread

“…The unique terminal Nap-covered structure plays an essential role in M. genitalium adherence to various eukaryotic cells [ 6 , 24 , 25 ], as evidenced by the polarity of mycoplasma terminal organelle-mediated adhesion events and the nature of some adhesin proteins, such as P140 [ 24 ]. Additionally, the Nap adhesion complex participates in a unique type of gliding motility in M. genitalium via a conformative alternation-dependent mechanism [ 6 , 25 ]. Furthermore, Nap exhibits strong immunoreactivity as the primary target of antibody reactions; however, it is worth noting that P140 and P110 are susceptible to antigenic variation, which allows them to evade host immune recognition [ 6 , 26 ].…”

“…P140 is a transmembrane adhesin that contains a large N -domain and a small C-domain, followed by a transmembrane helix required for attachment to host cells [ 25 ]. The N -terminal domain consists of a seven-bladed (β-sheet) propeller and a “crown” formed by the clustering of long polypeptide segments that emerge from the propeller [ 6 , 25 ]. Interestingly, the N -domain of P140 likely represents the signal peptide, as it corresponds to the predicted signal sequence, and the end of N-domain contains a few disordered residues.…”

“…Furthermore, a malleable region has been identified in the C- domain, which is sensitive to interaction with the N-domain, whereas the transmembrane helix connects the region free from the influence of N-domain interactions [ 36 ]. It was found that the N- and C-domains move relative to one another and act as important components in the conformational transitions of Nap during adhesion to host receptors [ 25 , 36 , 37 ]. Owing to the high homology between P140 of M. genitalium and P1 adhesin of M. pneumoniae , these cross-reactive epitopes show biological and immunological similarities [ 31 , 38 ].…”

“…Aparicio et al used cryo-electron microscopy and tomography to show that Nap can exist in a “closed” or “open” conformation, which may lead to structural rearrangements and is crucial for cytadherence and release to cell receptors [ 6 ]. The unique terminal Nap-covered structure plays an essential role in M. genitalium adherence to various eukaryotic cells [ 6 , 24 , 25 ], as evidenced by the polarity of mycoplasma terminal organelle-mediated adhesion events and the nature of some adhesin proteins, such as P140 [ 24 ]. Additionally, the Nap adhesion complex participates in a unique type of gliding motility in M. genitalium via a conformative alternation-dependent mechanism [ 6 , 25 ].…”

“…Mutation in P140 results in a cytadherence-negative phenotype, emphasizing the importance of P140 in M. genitalium pathogenesis [ 19 ]. P140 is a transmembrane adhesin that contains a large N -domain and a small C-domain, followed by a transmembrane helix required for attachment to host cells [ 25 ]. The N -terminal domain consists of a seven-bladed (β-sheet) propeller and a “crown” formed by the clustering of long polypeptide segments that emerge from the propeller [ 6 , 25 ].…”