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C-terminal Mad Homology 2 (MH2) domain in SMAD6 The MH2 domain is located at the C-terminus of the SMAD (small mothers against decapentaplegic) family of proteins, which are signal transducers and transcriptional modulators that mediate multiple signaling pathways. The MH2 domain is responsible for type I receptor interaction, phosphorylation-triggered homo- and hetero-oligomerization, and transactivation. It is negatively regulated by the N-terminal MH1 domain, which prevents it from forming a complex with SMAD4. SMAD6, an inhibitory or antagonistic SMAD (I-SMAD), acts as a negative regulator of signaling mediated by the TGF-beta superfamily of ligands, by competing with SMAD4 and preventing the transcription of SMAD4's gene products. SMAD6 specifically inhibits bone morphogenetic protein (BMP) type I receptor mediated signaling. SMAD6 and SMAD7 act as critical mediators for effective TGF-beta I-mediated suppression of Interleukin-1/Toll-like receptor (IL-1R/TLR) signaling through simultaneous binding to Pellino-1, an adaptor protein of interleukin-1 receptor associated kinase 1 (IRAK1), via their MH2 domains. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",