A c-di-GMP binding effector STM0435 modulates flagellar motility and pathogenicity in Salmonella

ABSTRACT

Flagella play a crucial role in the invasion process of Salmonella and function as a significant antigen that triggers host pyroptosis. Regulation of flagellar biogenesis is essential for both pathogenicity and immune escape of Salmonella. We identified the conserved and unknown function protein STM0435 as a new flagellar regulator. The ∆stm0435 strain exhibited higher pathogenicity in both cellular and animal infection experiments than the wild-type Salmonella. Proteomic and transcriptomic analyses demonstrated dramatic increases in almost all flagellar genes in the ∆stm0435 strain compared to wild-type Salmonella. In a surface plasmon resonance assay, purified STM0435 protein-bound c-di-GMP had an affinity of ~8.383 µM. The crystal structures of apo-STM0435 and STM0435&c-di-GMP complex were determined. Structural analysis revealed that R33, R137, and D138 of STM0435 were essential for c-di-GMP binding. A Salmonella with STM1987 (GGDEF protein) or STM4264 (EAL protein) overexpression exhibits completely different motility behaviours, indicating that the binding of c-di-GMP to STM0435 promotes its inhibitory effect on Salmonella flagellar biogenesis.

KEYWORDS:

• Salmonella typhimurium
• c-di-GMP
• STM0435
• flagellar biosynthesis
• virulence

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

BL contributed to the conception and design of the study. WW conceived and drafted the manuscript. YD, RL, YY, and NS conducted the study. YD, MZ, and HJ performed structural analyses. RL, XL, and ZM performed the sequence analyses. QL, XL, and XG performed statistical analyses. All authors have contributed to the manuscript and approved the submitted version.

Data Availability statement

The X-ray structures (coordinates and structure factor files) of STM0435 were submitted to the PDB under accession numbers 8K4I (Apo-STM0435) and 8K5Q (STM0435-c-di-GMP). Proteomic data were submitted to ProteomeX change via the PRIDE database (https://proteomecentral.proteomexchange.org/cgi/GetDataset?ID=PXD044133). The transcriptional data were submitted to the GEO database (https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE239303). Original data for this study can be found in the Mendeley Dataset (http://doi.org/10.17632/wvm6scwmdt.1).

Supplemental data

Supplemental data for this article can be accessed online at https://doi.org/10.1080/21505594.2024.2331265.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [32170034 to B.Q.L., 81902038 to W.W.W.], Special Fund for Taishan Scholars Program [tsqn202211216 to B.Q.L.], Shandong Excellent Youth Fund [ZR2023YQ060 to B.Q.L.], Academic Promotion Program of Shandong First Medical University [2019LJ001 to B.Q.L.], and Natural Science Foundation of Shandong Province [ZR2023MH095 to Y.Y.Y.]. Youth Innovation Technology Program innovation team of Shandong Provincial University [2023KJ170 to W.W.W.].