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The Porphyromonas gingivalis type IX secretion system (T9SS) is a recently discovered protein secretion system that is widely distributed in Bacillus cereus. The T9SS is structurally complex and powerful. More than 20 T9SS components have been verified, and more than 30 virulence factors can be secreted by Porphyromonas gingivalis alone, which contributes significant to the pathogenicity of Porphyromonas gingivalis. T9SS is a large protein complex spanning the inner cell membrane, periplasm, and outer cell membrane. Through the structural and functional connections among its components, it forms a sophisticated functional complex that includes power provision, energy transduction, inner and outer membrane translocation, outer membrane modification, and regulatory systems to recognize, translocate, shear, and modify cargo proteins and translocate bacterial intracellular cargo proteins to the cell surface. In recent years, with advancements in X-ray diffraction and in situ cryoelectron microscopy, the exploration of T9SS has evolved from the functional study of single components to the in situ structural study of multiprotein complexes. Still, the structural resolution of the protein still has shortcomings such as low resolution and an inability to capture dynamic functional structures. Future research directions should focus more on exploring how T9SS interacts and functions with cargo proteins. In this paper, we review the research progress on Porphyromonas gingivalis T9SS on X-ray diffraction and cryoelectron microscopy structure resolution in order to gain a deeper understanding of the transport mechanism of T9SS.

Objective. To prepare and crystallize a novel oral bacterial serine protease inhibitor Tannerpin with high purity by means of biochemistry and structural biology. Methods. A novel serine protease inhibitor was screened from periodontal disease-related bacteria by amino acid sequence analysis, and named as Tannerpin. The fusion expression vector pSUMO3-Tannerpin was constructed and transferred into E. coli BL21 (DE3) system for induction expression. Tannerpin was isolated and purified by a combination of nickel-affinity chromatography, SUMO-specific protease 2 (SENP2) digestion and gel filtration chromatography, and was verified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Then, the crystallization conditions of the purified protein were screened and optimized, and its acting substrates were screened. Results. SDS-PAGE showed that SUMO3-Tannerpin fusion protein was successfully expressed in E. coli. After removing the fusion label of the protein by purification scheme, Tannerpin with relative molecular weight of about 43 000 was obtained. After crystallization screening and optimization, Tannerpin crystals with a resolution of 1.7 Å were finally obtained under the conditions of 20 °C, pH=6.0, precipitant of 28% polyethylene glycol 3350 and 8% Tacsimate. However, the acting substrate of Tannerpin was not obtained. Conclusion. A novel serine protease inhibitor Tannerpin secreted by oral bacteria and its crystal are successfully prepared, which may lay a foundation for subsequent structural analysis and functional study. [ABSTRACT FROM AUTHOR]

Epigenetics refers to a steady change in the level of gene expression caused by non-DNA sequence changes. Microbes can modulate host inflammation through epigenetic pathways to evade or expend immune responses. As an important part of human microbes, oral bacteria also have various epigenetic regulation mechanisms to affect host inflammatory responses. This article reviews the common pathways of epigenetic regulation in microbe infection and the regulation of host epigenetics by using oral microbes to provide a reference for the study of epigenetic-related mechanisms in oral diseases.