Acidic pH irreversibly activates the signaling enzyme SARM1. (13th July 2021)

• Record Type: Journal Article
• Authors: Zhao, Yong Juan; He, Wei Ming; Zhao, Zhi Ying; Li, Wan Hua; Wang, Qian Wen; Hou, Yun Nan; Tan, Yongjun; Zhang, Dapeng
• Is Part Of: FEBS journal. Volume 288:Number 23(2021)
• Page Start: 6783
• Page End: 6794
• Publication Date: 2021-07-13
• Subjects: acid‐induced activation -- E689Q -- nicotinamide mononucleotide -- PC6 -- R216Q -- SARM1; Biochemistry -- Periodicals; Molecular biology -- Periodicals; Pathology, Molecular -- Periodicals; 572
• DOI: 10.1111/febs.16104
• Languages: English
• ISSNs: 1742-464X

Abstract

Abstract : SARM1, an executioner in axon degeneration, is an autoinhibitory NAD‐consuming enzyme, composed of multiple domains. NMN and its analogs, CZ‐48 and VMN, are the only known activators, which can release the inhibitory ARM domain from the enzymatic TIR domain. Here, we document that acid can also activate SARM1, even more efficiently than NMN, possibly via the protonation of the negative residues. Systematic mutagenesis revealed that a single mutation, E689Q in TIR, led to the constitutive activation of SARM1. It forms a salt bridge with R216 in the neighboring ARM, maintaining the autoinhibitory structure. Using this 'acid activation' protocol, mutation K597E was found to inhibit activation, while H685A eliminated SARM1 catalytic activity, revealing two distinct inhibitory mechanisms. The protocol has also been applied to differentiate two classes of chemical inhibitors. NAD, dHNN, disulfiram, CHAPS, and TRX‐100 mainly inhibited the activation process, while nicotinamide and Tweens mainly inhibited SARM1 catalysis. Taken together, we demonstrate a new mechanism for SARM1 activation and decipher two distinct inhibitory mechanisms of SARM1. Abstract : This study demonstrated that acidic pH activates the NAD signaling enzyme SARM1. Constitutive activation of the mutants mimicking the protonation of the negative residues upon acid treatment reveals a potential salt bridge formed between R216 and E689 in the inhibited conformation. Since the acid‐induced activation is independent of NMN binding and irreversible, the protocol can be applied in studying the structural or modulatory mechanisms of SARM1.