ubiquitin-like (Ubl) domain found in a group of small sulfide carrier proteins
Ubiquitin-like (Ubl) domain found in a group of small sulfide carrier proteins This family includes ThiS, MoaD, CysO, QbsE, and their homologs, which are structurally homologous to ubiquitin (Ub) and may function as the sulfide donor for the biosynthesis of thiamin, molybdopterin, cysteine, thioquinolobactin, and other sulfur-containing natural products. Ub is a protein modifier in eukaryotes that is involved in various cellular processes, including transcriptional regulation, cell cycle control, and DNA repair. Ubiquitination is comprised of a cascade of E1, E2 and E3 enzymes that results in a covalent bond between the C-terminus of Ub and the epsilon-amino group of a substrate lysine. Like Ub, small sulfide carrier proteins in this family are adenylated at a diglycyl C-terminus by specific activating proteins. The adenylated C-terminus is subsequently converted to a thiocarboxylate, serving as the sulfide source. Those activating proteins are diverse and show little sequence similarity. This family also includes the small archaeal modifier protein (SAMP), including SAMP1, SAMP2 and SAMP3, which are Ub-like proteins that function as protein modifiers and are required for the production of sulfur-containing biomolecules in the archaeon Haloferax volcanii. SAMP1 and SAMP2 are involved in sulfur transfer during molybdenum cofactor biosynthesis and tRNA thiolation much like MoaD and Urm1, respectively. They can form covalent conjugates with their protein targets through an isopeptide linkage via their C-terminal diglycine motif in a streamlined archaeal E1-dependent pathway. SAMP2 also forms homo-conjugates through the intermolecular isopeptide bond between the C-terminal Gly and the Lys58 side chain, a feature that likely resembles polyubiquitination. SAMP3 conjugates are dependent on the Ub-activating E1 enzyme homolog of archaea (UbaA) for synthesis and are cleaved by the JAMM/MPN+ domain metalloprotease HvJAMM1.
Comment:the MoaD-MoaB, MoaD-MoaE, ThiS-ThiF, ThiS-ThiG, CysO-BexX and CysO-CysM interaction surfaces appear similar to that of other beta-grasp protein complexes
Structure:1ZUD; Escherichia coli ThiS interacts with thiazole biosynthesis adenylyltransferase ThiF, contacts at 4A - View structure with Cn3D
Comment:ThiS is a small protein that structurally resembles ubiquitin and the molybdopterin biosynthetic protein MoaD; ThiF has distinct sequence and structural similarity to the ubiquitin activating enzyme E1 and the molybdopterin biosynthetic protein MoeB; ThiS and ThiF are bacterial proteins involved in the synthesis of the thiazole moiety of thiamin
Jiyao W et al.(2023). "The conserved domain database in 2023.",