Periplasmic gatekeeping of phage DNA entry by rSAM enzyme-mediated maturation of an effector with His-X-Ser repeats

Li, M.; Sun, E.; Wang, S.; Huang, Y.; Song, H.; Kuang, S.; Li, G.; Liu, Y.; Xia, Z.; Zhang, X.; Han, J.; Dong, Z.; Rao, V. B.; Sun, L.; Tao, P.

doi:10.64898/2026.01.06.697848

bioRxiv · 10.64898/2026.01.06.697848

Periplasmic gatekeeping of phage DNA entry by rSAM enzyme-mediated maturation of an effector with His-X-Ser repeats

Li, M.·Sun, E.·Wang, S.·Huang, Y.·Song, H.·Kuang, S.·Li, G.·Liu, Y.·Xia, Z.·Zhang, X.·Han, J.·Dong, Z.·Rao, V. B.·Sun, L.·Tao, P.

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Abstract

In the relentless arms race between bacteria and phages, bacteria have evolved a variety of defense strategies to combat phage infection. However, no bacterial system has been identified that specifically target the phage DNA entry phase. Here, we present a novel bacterial antiphage system, termed HXS, which provides broad-spectrum and robust antiphage activity by interfering with phage DNA entry. The HXS system consists of two radical S-adenosylmethionine (rSAM) enzymes (HxsB and HxsC), a small protein (HxsD), and the effector HxsA with a peptidoglycan-binding domain and five His-Xaa-Ser (HXS) repeats. HxsB/HxsC catalyze rSAM enzyme-dependent maturation of HxsA, including N-terminal processing and a site-specific +8 Da modification, thereby producing a periplasmic effector required for HXS defense. Biochemical evidence supports a model in which the matured effector likely engages incoming DNA electrostatically to arrest entry, establishing an rSAM enzyme-modified protein effector in antiphage defense.

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Li, M., Sun, E., Wang, S., Huang, Y., Song, H., Kuang, S., Li, G., Liu, Y., Xia, Z., Zhang, X., Han, J., Dong, Z., Rao, V. B., Sun, L., Tao, P.. 2026-01-06. Periplasmic gatekeeping of phage DNA entry by rSAM enzyme-mediated maturation of an effector with His-X-Ser repeats. https://doi.org/10.64898/2026.01.06.697848

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