SIRT5-mediated desuccinylation of the porcine deltacoronavirus M protein drives pexophagy to enhance viral proliferation.

Porcine deltacoronavirus (PDCoV) is an emerging enteropathogenic coronavirus capable of infecting various animal species, including humans. In this study, we explored the roles of sirtuins (SIRTs), a conserved family of protein deacylases and mono-adenosine diphosphate-ribosyltransferases, in PDCoV replication. Surprisingly, we found that SIRT5-a unique member of SIRTs with distinct desuccinylation, demalonylation, and deglutarylation activities-is a proviral factor essential for PDCoV replication; its catalytic activities are crucial in this process. Mechanistically, SIRT5 interacts with and desuccinylates the PDCoV membrane (M) protein. This modification activates the ataxia-telangiectasia mutated (ATM) pathway, facilitates ubiquitination of peroxisomal biogenesis protein 5 (PEX5), and recruits sequestosome 1 (SQSTM1/p62) to initiate selective peroxisomal autophagy (pexophagy). The pexophagy process disrupts peroxisomal function, elevates reactive oxygen species (ROS) levels, and suppresses type I and III interferon production, thereby enhancing viral replication. We also identified lysine 207 (K207) as the primary succinylation site of the M protein. Mutations mimicking the desuccinylated or succinylated states of K207 substantially influence viral replication and the ability to induce pexophagy. These findings reveal a novel role for SIRT5 in regulating pexophagy during viral infection and suggest a therapeutic target for efforts to combat coronavirus infections.