Mechanisms and Regulation of Intracellular Proteolysis

Th e proteins which make up the cells and tissues of living organisms are constantly being made and broken- down. Under normal conditions the rates of these processes are equal and there is no net change in the protein composition of cells. However, under many conditions either or both of these processes do change and lead to changes in the protein composition of cells . We are interested in understanding the specific biochemical mechanisms for the breakdown of proteins. We have already identified an enzyme named macropain that is capable o f this function . This enzyme has a number of features which are similar to what is known about the process of protein breakdown in intact cells and therefore we believe that it is an excellent candidate for an important component of this process. Our work deals with the study of this enzyme. We will use a cell system which we can easily manipulate experimentally in order to examine the function of macropain. We will test the hypothesis that macropain attacks cellular proteins that are “tagged” by another cellular protein, ubiquitin. We believe that this work will provide basic information about a fundamental cellular process, and may also provide critical insights to neuropathologies such as Alzheimer’s disease (AD). For example, there is evidence that one of the features of AD is the accumulation of various ubiquitin-tagged proteins. Therefore, something may go wrong with cellular protein breakdown systems in AD. These accumulated proteins which normally should be degraded, may interfere with important cellular processes. By knowing the features of protein breakdown under normal conditions, our work may ultimately allow us to identify cellular defects in AD and thus serve as a possible basis for understanding or even treatment of this disease.