Essential protein P116 extracts cholesterol and other indispensable lipids for Mycoplasmas

Mycoplasma pneumoniae, responsible for approximately 30% of community-acquired human pneumonia, needs to extract lipids from the host environment for survival and proliferation. Here, we report a comprehensive structural and functional analysis of the previously uncharacterized protein P116 (MPN_213). Single-particle cryo-electron microscopy of P116 reveals a homodimer presenting a previously unseen fold, forming a huge hydrophobic cavity, which is fully accessible to solvent. Lipidomics analysis shows that P116 specifically extracts lipids such as phosphatidylcholine, sphingomyelin and cholesterol. Structures of different conformational states reveal the mechanism by which lipids are extracted. This finding immediately suggests a way to control Mycoplasma infection by interfering with lipid uptake.

The Sialoglycan Binding Adhesins of Mycoplasma genitalium and Mycoplasma pneumoniae

Mycoplasma genitalium (Mge) and Mycoplasma pneumoniae (Mpn) are two human pathogens associated with urogenital and respiratory tract infections, respectively. The recent elucidation of the tridimensional structure of their major cytoadhesins by X-ray crystallography and cryo-electron microscopy/tomography, has provided important insights regarding the mechanics of infection and evasion of immune surveillance.

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

Mycoplasma pneumoniae is a bacterial human pathogen that causes primary atypical pneumonia. M. pneumoniae motility and infectivity are mediated by the immunodominant proteins P1 and P40/P90, which form a transmembrane adhesion complex. Here we report the structure of P1, determined by X-ray crystallography and cryo-electron microscopy, and the X-ray structure of P40/P90. Contrary to what had been suggested, the binding site for sialic acid was found in P40/P90 and not in P1. Genetic and clinical variability concentrates on the N-terminal domain surfaces of P1 and P40/P90. Polyclonal antibodies generated against the mostly conserved C-terminal domain of P1 inhibited adhesion of M. pneumoniae, and serology assays with sera from infected patients were positive when tested against this C-terminal domain. P40/P90 also showed strong reactivity against human infected sera. The architectural elements determined for P1 and P40/P90 open new possibilities in vaccine development against M. pneumoniae infections.

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

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.

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

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.