Protein quality control and ubiquitin proteasome system: implications on cataract

Abstract

Purpose Accumulation of damaged or abnormal proteins is cytotoxic and is causally related to various age-related diseases, including cataract. The objective of this study is to investigate the effect of 19S regulatory complexes on the fate of damaged proteins. Methods The denaturation of firefly luciferase (a model protein) was performed at 43°C during 10 min in the presence of Hsp90 and denaturation of luciferase was monitored by the loss of its enzymatic activity. Luciferase activity in the cells was determined to monitor the refolding of denatured luciferase at 30°C in the presence or absence of ubiquitination system. Results The data showed that heat-denatured luciferase was preferentially ubiquitinated and degraded by the UPP as compared with the native form. Inhibition of the ubiquitination or proteolysis enhanced renaturation. The 19S regulatory complex enhances renaturation of denatured substrate in the presence of ubiquitinating activity. The data also suggested that recognition of a poliubiquitinated substrate requires that polyubiquitin chain interact with specific domains of the 19S cap of the proteasome and this interaction play an important role on the fate of denatured proteins. Additionally, the data shown that are critical lysines in the ubiquitin moiety are required for an efficient and productive interaction with proteasome. Conclusion Failure in the protein quality control system is likely to have important implication in loss of lens transparency and cataract formation.