Proteolysis by the ubiquitin-proteasome system and kidney disease.

Proteins in all cells turnover continuously such that rigorous control of proteolysis is required to govern levels of proteins with vastly different half-lives and actions including those regulating transcription, metabolic pathways, or the breakdown of muscle proteins to amino acids used in gluconeogenesis or the synthesis of new proteins. Critical cellular functions would be disrupted without precise regulation of protein degradation. Thus, it is surprising that the bulk of protein in all cells is degraded by the ATP-dependent, ubiquitin-proteasome system. The system achieves remarkable specificity by selective conjugation of ubiquitin (Ub) to a doomed protein in a process catalyzed by >1000 ubiquitin ligases that recognize individual substrate proteins. Because the pathogenesis of certain kidney diseases and their complications are linked to the function of the ubiquitin-proteasome system, understanding its mechanisms could lead to novel therapies.