Evolutionary History of Alzheimer Disease-Causing Protein Family Presenilins with Pathological Implications

Presenilin proteins make the catalytic component of γ-secretase, a multiprotein transmembrane protease, and are type II transmembrane proteins. Amyloid protein, Notch, and beta catenin are among more than 90 substrates of Presenilins. Mutations in Presenilins lead to defects in proteolytic cleavage of its substrate resulting in some of the most devastating pathological conditions including Alzheimer disease (AD), developmental disorders, and cancer. In addition to catalytic roles, Presenilin protein is also shown to be involved in many non-catalytic roles, i.e., calcium homeostasis, regulation of autophagy, and protein trafficking, etc. These proteolytic proteins are highly conserved and are present in almost all the major eukaryotic groups. Studies, performed on a wide variety of organisms ranging from human to unicellular dictyostelium, have shown the important catalytic and non-catalytic roles of Presenilins. In this study, we infer the evolutionary patterns and history of Presenilins as well as of other γ-secretase proteins. We show that Presenilins are the most ancient of the γ-secretase proteins and that Presenilins may have their origin in the last common ancestor (LCA) of Eukaryotes. We also demonstrate that Presenilin proteins generally lack diversifying selection during the course of their evolution. Through evolutionary trace analysis, we show that Presenilin protein sites that undergo mutations in Familial Alzheimer disease, are highly conserved in metazoans. Finally, we discuss the evolutionary, physiological, and pathological implications of our findings and propose that the evolutionary profile of Presenilins supports the loss of function hypothesis of AD pathogenesis.