Structure and mechanism of the Nap adhesion complex from the human pathogen Mycoplasma genitalium

Abstract

Mycoplasma genitalium is a human pathogen adhering to host target epithelial cells and causing urethritis, cervicitis and pelvic inflammatory disease. Essential for infectivity is a transmembrane adhesion complex called Nap comprising proteins P110 and P140. Here we report the crystal structure of P140 both alone and in complex with the N-terminal domain of P110. By cryo-electron microscopy (cryo-EM) and tomography (cryo-ET) we find closed and open Nap conformations, determined at 9.8 and 15 Å, respectively. Both crystal structures and the cryo-EM structure are found in a closed conformation, where the sialic acid binding site in P110 is occluded. By contrast, the cryo-ET structure shows an open conformation, where the binding site is accessible. Structural information, in combination with functional studies, suggests a mechanism for attachment and release of M. genitalium to and from the host cell receptor, in which Nap conformations alternate to sustain motility and guarantee infectivity.

Immunodominant proteins P1 and P40/P90 from human pathogen Mycoplasma pneumoniae

“…8) although, according to in vivo studies, 6SL binds at a much lower affinity than 3SL 37,38 . For P1, SPR shows no binding to sialylated oligosaccharides, in agreement with what is observed for M. genitalium 17 .…”

“…In the Nap, the conformational changes required by the foot/leg activity during gliding have to be synchronized with the binding/release to the cell receptors, which are thought to be randomly distributed on the host surface. The binding site in P40/P90 could be regulated by the interaction with P1 as found in M. genitalium 17 . This may be the reason why P1 was expected to contain the binding site.…”

“…The crystals from P1 belong to space group C2 and could contain, by packing considerations, only one subunit in the asymmetric unit. We tried to solve these P1 crystals by heavy atoms and SeMet derivatives, but finally the resolution was achieved by density modification techniques applying solvent flattening and averaging with crystals from the M. genitalium orthologous protein P140, whose structure was also unknown at that time 17 . With this procedure the structures of P1 and of P140 (with a sequence identity of 41% between their ectodomains) were solved simultaneously.…”

“…P140 and P110 are the M. genitalium orthologues of P1 and P40/P90, respectively. Therefore, it was most unexpected to find that in M. genitalium the binding site for sialic acid oligosaccharides is in P110 and not in P140 17,18 . P1 is considered to be one of the most immunodominant proteins in M. pneumoniae cells, playing a major role in the immune response of infected patients and accordingly in diagnosis and epidemiologic studies 3,19,20 .…”

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

“…Mycoplasma genitalium, the causative agent of urethritis in men and cervicitis and pelvic inflammatory disease in women, presents arguably the smallest genome amongst organisms that are capable of self-replication and axenic growth (McGowin & Anderson-Smits, 2011;Glass et al, 2006). The adherence of M. genitalium to host target epithelial cells is mediated by an $0.5 MDa transmembrane complex called Nap, which is composed of a dimer of the heterodimer formed by the P110 and P140 proteins (Aparicio et al, 2018(Aparicio et al, , 2020Burgos et al, 2006;Mernaugh et al, 1993;Scheffer et al, 2017). In M. genitalium and in other members of the pneumonia cluster of mycoplasmas, such as the important human pathogen M. pneumoniae, the Nap adhesion complex also participates in a unique type of gliding cell motility that is essential for infectivity (Krause, 1996;Krause & Baseman, 1982;Radestock & Bredt, 1977;Burgos et al, 2006;García-Morales et al, 2016;Nakane et al, 2011;Seto et al, 2005).…”