The Many Substrates of Presenilin/gamma-Secretase

The Alzheimer's disease (AD)-associated amyloid-beta protein precursor (A beta PP) is cleaved by alpha-, beta-, and presenilin (PS)/gamma-secretases through sequential regulated proteolysis. These proteolytic events control the generation of the pathogenic amyloid-beta (A beta) peptide, which excessively accumulates in the brains of individuals afflicted by AD. A growing number of additional proteins cleaved by PS/gamma-secretase continue to be discovered. Similarly to A beta PP, most of these proteins are type-I transmembrane proteins involved in vital signaling functions regulating cell fate, adhesion, migration, neurite outgrowth, or synaptogenesis. All the identified proteins share common structural features, which are typical for their proteolysis. The consequences of the PS/gamma-secretase-mediated cleavage on the function of many of these proteins are largely unknown. Here, we review the current literature on the proteolytic processing mediated by the versatile PS/gamma-secretase complex. We begin by discussing the steps of A beta PP processing and PS/gamma-secretase complex composition and localization, which give clues to how and where the processing of other PS/gamma-secretase substrates may take place. Then we summarize the typical features of PS/gamma-secretase-mediated protein processing. Finally, we recapitulate the current knowledge on the possible physiological function of PS/gamma-secretase-mediated cleavage of specific substrate proteins.