Biology subjects

Sherif, A. A.

Publications and source records attributed to Sherif, A. A..

3 recordsLinked to original sources

bioRxiv2022

Structural basis of Irgb6 inactivation by Toxoplasma gondii through the phosphorylation of switch I.

Upon infection with Toxoplasma gondii, host cells produce immune-related GTPases (IRGs) to kill the parasite. T. gondii counters this response by releasing ROP18 kinase, which inactivates IRG GTPases and inhibits their recruitment to the T. gondii parasitophorous vacuole (PV). However, the molecular mechanisms of this process are entirely unknown. Here we report the atomic structures of Irgb6 with a phosphomimetic mutation by ROP18. The mutant has lower GTPase activity and is not recruited to the PV membrane (PVM). The crystal structure shows the mutant exhibit a distinct conformation from the physiological nucleotide-free form, thus preventing GTPase cycling. This change allosterically modifies the conformation of the membrane-binding interface, preventing physiological PVM-binding. Docking simulation of PI5P also supports the impaired binding of the mutant to PVM. We thus demonstrate the structural basis for T. gondii escape from host cell-autonomous defense, and provide a structural model for regulating enzymatic activity by phosphorylation.

microbiology↗

bioRxiv2022

TCR binding to a peptide-MHC complex raises a drawbridge for CD3 cross-membrane signaling

In this study, we present an allosteric mechanism for T cell receptor (TCR) triggering upon binding a peptide-MHC complex (pMHC), in which a conformational change in the TCR upon pMHC binding controls the mobility of the CD3 proteins. We found that the TCR{beta} FG loop serves as a gatekeeper, preventing accidental triggering, while the connecting peptide acts as a hinge for essential conformational changes in the TCR. Atomistic simulations and cell-based experiments with genetically modified connecting peptides demonstrate that rigidified hinge residues result in excessive CD3 dynamics and hypersensitivity to pMHC binding. Our model thus provides a clear connection between extracellular TCR-pMHC binding and changes in CD3 dynamic that propagate from outside to inside the cell.

molecular biology↗

bioRxiv2021

Structural basis of membrane recognition of Toxoplasma gondii vacuole by Irgb6

The p47 immunity-related GTPase (IRG) Irgb6 plays a pioneering role in host defense against Toxoplasma gondii infection. It is recruited to the parasitophorous vacuole membrane (PVM) formed by T. gondii and disrupts it. Despite the importance of this process, the molecular mechanisms accounting for PVM recognition by Irgb6 remain elusive due to lack of structural information on Irgb6. Here we report the crystal structures of mouse Irgb6 in the GTP-bound and nucleotide-free forms. Irgb6 exhibits a similar overall architecture to other IRGs in which GTP-binding induces conformational changes in both the dimerization interface and the membrane-binding interface. The membrane-binding interface of Irgb6 assumes a unique conformation, composed of N- and C-terminal helical regions forming a phospholipid binding site. In silico docking of phospholipids further revealed membrane binding residues that were validated through mutagenesis and cell-based assays. Collectively, these data demonstrate a novel structural basis for Irgb6 to recognize T. gondii PVM in a manner distinct from other IRGs. SummaryUpon Toxoplasma gondii infection, Irgb6 is recruited to the parasitophorous vacuole membrane (PVM) where it disrupts it. We solved the atomic structures of Irgb6 in two distinct nucleotide states, revealing a unique PVM binding interface sensitive to the GTPase cycling.

microbiology↗