Small archaeal modifier protein 2
Haloferax volcanii (strain ATCC 29605 / DSM 3757 / JCM 8879 / NBRC 14742 / NCIMB 2012 / VKM B-1768 / DS2)
Functions as a protein modifier covalently attached to lysine residues of substrate proteins, as well as a sulfur carrier in tRNA thiolation. The protein modification process is termed sampylation and involves the formation of an isopeptide bond between the SAMP2 C-terminal glycine carboxylate and the epsilon-amino group of lysine residues on target proteins. Is able to form polymeric chains with itself at Lys-58, similar to ubiquitin and other ubiquitin-like proteins. May serve as a proteolytic signal in the cell to target proteins for degradation by proteasomes.