SAM (sterile alpha motif) domain of STIM1 (Stromal interaction molecule) subfamily proteins is a putative protein-protein interaction domain. STIM1 and STIM2 human proteins are type I transmembrane proteins. The N-terminal part of them includes "hidden" EF-hand and SAM domains. This region is responsible for sensing changes in store-operated and basal cytoplasmic Ca2+ levels and initiates oligomerization. "Hidden" EF hand and SAM domains have a stable intramolecular association, and the SAM domain is a component that regulates stability within STIM proteins. Destabilization of the EF-SAM association during Ca2+ depletion leads to partial unfolding and aggregation (homooligomerization), thus activating the store-operated Ca2+ entry. Immunoprecipitation analysis indicates that STIM1 and STIM2 can form co-precipitable oligomeric associations in vivo. It was suggested that STIM1 protein is an activator of store operated channels in plasma membrane.
Comment:Highlighted residues drive SAM aggregation by formation SAM/SAM intermolecular contacts coupled with destabilization of the entire EF-SAM entity upon Ca depletion (based on mutagenesis).
Jiyao W et al.(2023). "The conserved domain database in 2023.",