Suppression of innate antiviral response by severe acute respiratory syndrome coronavirus M protein is mediated through the first transmembrane domain

Coronaviruses have developed various measures to evade innate immunity, We have previously shown that severe acute respiratory syndrome （SARS） coronavirus M protein suppresses type I interferon （IFN） production by impeding the formation of functional TRAF3-containing complex. In this study, we demonstrate that the IFN-antagonizing activity is specific to SARS coronavirus M protein and is mediated through its first transmembrane domain （TM 1） located at the N terminus. M protein from human coronavirus HKU 1 does not inhibit IFN production. Whereas N-linked glycosylation of SARS coronavirus M protein has no influence on IFN antagonism, TM1 is indispensable for the suppression of IFN production. TM 1 targets SARS coronavirus M protein and heterologous proteins to the Golgi apparatus, yet Golgi localization is required but not sufficient for IFN antagonism. Mechanistically, TM 1 is capable of binding with RIG-I, TRAF3, TBK1 and IKK~, and preventing the interaction of TRAF3 with its downstream effectors. Our work defines the molecular architecture of SARS coronavirus M orotein reouired for suooression of innate antiviral re~nnn~e.