Maupin-Furlow Julie A
Department of Microbiology and Cell Science, University of Florida, Gainesville, Florida 32611; email:
Annu Rev Microbiol. 2014;68:155-75. doi: 10.1146/annurev-micro-091313-103447. Epub 2014 May 29.
Prokaryotes form ubiquitin (Ub)-like isopeptide bonds on the lysine residues of proteins by at least two distinct pathways that are reversible and regulated. In mycobacteria, the C-terminal Gln of Pup (prokaryotic ubiquitin-like protein) is deamidated and isopeptide linked to proteins by a mechanism distinct from ubiquitylation in enzymology yet analogous to ubiquitylation in targeting proteins for destruction by proteasomes. Ub-fold proteins of archaea (SAMPs, small archaeal modifier proteins) and Thermus (TtuB, tRNA-two-thiouridine B) that differ from Ub in amino acid sequence, yet share a common β-grasp fold, also form isopeptide bonds by a mechanism that appears streamlined compared with ubiquitylation. SAMPs and TtuB are found to be members of a small group of Ub-fold proteins that function not only in protein modification but also in sulfur-transfer pathways associated with tRNA thiolation and molybdopterin biosynthesis. These multifunctional Ub-fold proteins are thought to be some of the most ancient of Ub-like protein modifiers.
原核生物通过至少两种不同的、可逆且受调控的途径，在蛋白质的赖氨酸残基上形成类泛素（Ub）异肽键。在分枝杆菌中，Pup（原核类泛素蛋白）的C末端Gln发生脱酰胺作用，并通过一种在酶学上不同于泛素化但在靶向蛋白质被蛋白酶体降解方面类似于泛素化的机制与蛋白质形成异肽键。古菌的Ub折叠蛋白（SAMPs，小型古菌类修饰蛋白）和嗜热栖热菌的（TtuB，tRNA-双硫尿苷B）在氨基酸序列上与Ub不同，但具有共同的β-抓握折叠结构，它们也通过一种与泛素化相比显得更为简化的机制形成异肽键。研究发现，SAMPs和TtuB属于一小类Ub折叠蛋白，它们不仅在蛋白质修饰中起作用，还参与与tRNA硫醇化和钼蝶呤生物合成相关的硫转移途径。这些多功能Ub折叠蛋白被认为是一些最古老的类泛素蛋白修饰剂。
