Biology subjects

Yu, X.-J.

Publications and source records attributed to Yu, X.-J..

3 recordsLinked to original sources

bioRxiv2025

Salmonella effector kinase SteC is activated by host-mediated phosphorylation

The pathogen Salmonella, which causes significant human morbidity and mortality, encodes an effector kinase, SteC, which mediates actin polymerisation and cell migration. Given the minimal nature of its kinase domain, it remains unclear how SteC is catalytically active and how this activity is regulated. Here, we show that SteC is activated following the phosphorylation of the highly conserved S379 residue by a host kinase. Phosphorylation of S379 dramatically increases nucleotide binding affinity of SteC, enabling substrate phosphorylation and promoting actin polymerisation. Further mutational analysis identified the functional role of HD and DGD motifs that likely mimic the HxD and DFG motifs of eukaryotic kinases. Meanwhile, the C-tail of SteC, encompassing amino acids 429-457, is essential for function following translocation from Salmonella, but dispensable for catalysis in vitro. Overall, our findings uncover two previously unappreciated mechanisms that mediate the activity of the only Salmonella effector kinase within the host. HIGHLIGHTSSteC is phosphorylated at S379 in mammalian cells SteC phosphorylation is critical for kinase activity and actin polymerisation Phosphorylation at S379 promotes nucleotide binding The C-tail of SteC is not required for catalysis but is essential for activity in infected cells

microbiology↗

bioRxiv2023

Modulation of Salmonella virulence by a novel SPI-2 injectisome effector that interacts with the dystrophin-associated protein complex.

The injectisome encoded by Salmonella pathogenicity island 2 (SPI-2) had been thought to translocate 28 effectors. Here, we used a proteomic approach to characterise the secretome of a clinical strain of invasive non-typhoidal Salmonella enterica serovar Enteritidis, that had been mutated to cause hyper-secretion of the SPI-2 injectisome effectors. Along with many known effectors, we discovered the novel SseM protein. sseM is widely distributed between the five subspecies of Salmonella enterica, is found in many clinically-relevant serovars, and is co-transcribed with pipB2, a SPI-2 effector gene. Translocation of SseM required a functional SPI-2 injectisome. Following expression in human cells, SseM interacted with five components of the dystrophin-associated protein complex (DAPC), namely {beta}-2-syntrophin, utrophin/ dystrophin, -catulin, -dystrobrevin and {beta}-dystrobrevin. The interaction between SseM and {beta}-2-syntrophin and -dystrobrevin was verified in S. Typhimurium-infected cells and relied on the PDZ domain of {beta}-2-syntrophin and a sequence corresponding to a PDZ-binding motif (PBM) in SseM. A {Delta}sseM mutant strain had a small competitive advantage over the wild-type strain in the S. Typhimurium/mouse model of systemic disease. This phenotype was complemented by a plasmid expressing wild type SseM from S. Typhimurium or S. Enteritidis and was dependent on the PBM of SseM. Therefore, a PBM within a Salmonella effector mediates interactions with the DAPC and modulates systemic growth of bacteria in mice. ImportanceIn Salmonella enterica, the injectisome machinery encoded by Salmonella pathogenicity island 2 (SPI-2) is conserved among the five subspecies and delivers proteins (effectors) into host cells that are required for Salmonella virulence. The identification and functional characterisation of SPI-2 injectisome effectors advances our understanding of the interplay between Salmonella and its host(s). Using an optimised method for preparing secreted proteins and a clinical isolate of the invasive non-typhoidal (iNTS) Salmonella enterica serovar Enteritidis strain D24359, we identified 22 known SPI-2 injectisome effectors and one new effector - SseM. SseM modulates bacterial growth during murine infection and has a sequence corresponding to a PDZ-binding motif that is essential for interaction with the PDZ-containing host protein {beta}-2-syntrophin and other components of the dystrophin-associated protein complex (DAPC). To our knowledge, SseM is unique among Salmonella effectors in containing a functional PDZ-binding motif and is the first bacterial protein to target the DAPC.

microbiology↗

bioRxiv2020

Essential roles of plexin-B3+ oligodendrocyte precursor cells in the pathogenesis of Alzheimer's disease

The roles played by oligodendrocyte (OL) lineage cells, the largest glial population in the adult CNS, in the pathogenesis of Alzheimers disease (AD) remain elusive. Here, we show a newly developed culture method for adult OL progenitor cells (aOPCs) and identify novel plexin-B3-expressing (plexin-B3+) aOPCs as potential amyloid {beta} peptides (A{beta})-secreting cells. Fibroblast growth factor 2 (FGF2) promotes the survival and proliferation of aOPCs in a serum-free defined medium. Although the whole expression profiles of the expanded aOPCs closely resemble those of in vivo OPCs, we found a subpopulation (up to 5%) of plexin-B3+/olig2+ aOPCs in the cultures growing in FGF2. FGF2 withdrawal decreased NG2+, but increased plexin-B3+ aOPCs with increased APP expression, A{beta}1-40, -42 secretions and A{beta}1-42/total A{beta} ratios in association with cored senile plaque-like morphological changes. In vivo, plexin-B3+ aOPCs are distributed throughout the adult brain, although less densely so than NG2+ aOPCs. Spreading depolarization, a type of brain injury, induced unique delayed cortical plexin-B3+ aOPC gliosis in the ipsilateral, but not in the contralateral, remote cortex. In AD brains, virtually all senile plaques in the cortex were immunostained with plexin-B3 antibodies and the levels of cortical plexin-B3 expression increased significantly in the Salcosyl-soluble fractions. These findings suggest that plexin-B3+ aOPCs play important roles in the pathogenesis of AD most likely as a natural A{beta} source.

neuroscience↗