title: Intramembrane proteolysis by gamma-secretase.
abstract: Gamma-secretase mediates the final proteolytic cleavage, which liberates amyloid beta-peptide (Abeta), the major component of senile plaques in the brains of Alzheimer disease patients. Therefore, gamma-secretase is a prime target for Abeta-lowering therapeutic strategies. gamma-Secretase is a protein complex composed of four different subunits, presenilin (PS), APH-1, nicastrin, and PEN-2, which are most likely present in a 1:1:1:1 stoichiometry. PS harbors the catalytically active site, which is critically required for the aspartyl protease activity of gamma-secretase. Moreover, numerous familial Alzheimer disease-associated mutations within the PSs increase the production of the aggregation-prone and neurotoxic 42-amino acid Abeta. Nicastrin may serve as a substrate receptor, although this has recently been challenged. PEN-2 is required to stabilize PS within the gamma-secretase complex. No particular function has so far been assigned to APH-1. The four components are sufficient and required for gamma-secretase activity. At least six different gamma-secretase complexes exist that are composed of different variants of PS and APH-1. All gamma-secretase complexes can exert pathological Abeta production. Assembly of the gamma-secretase complex occurs within the endoplasmic reticulum, and only fully assembled and functional gamma-secretase complexes are transported to the plasma membrane. Structural analysis by electron microscopy and chemical cross-linking reveals a water-containing cavity, which allows intramembrane proteolysis. Specific and highly sensitive gamma-secretase inhibitors have been developed; however, they interfere with the physiological function of gamma-secretase in Notch signaling and thus cause rather significant side effects in human trials. Modulators of gamma-secretase, which selectively affect the production of the pathological 42-amino acid Abeta, do not inhibit Notch signaling.
authors.affiliation: Center for Integrated Protein Science Munich and Adolf Butenandt Institute, Department of Biochemistry, Laboratory for Neurodegenerative Disease Research, Ludwig Maximilians University, 80336 Munich, Germany. harald.steiner@med.uni-muenchen.de
authors.forename: Harald
authors.initials: H
authors.lastname: Steiner
authors.forename: Regina
authors.initials: R
authors.lastname: Fluhrer
authors.forename: Christian
authors.initials: C
authors.lastname: Haass
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism; D000595:Amino Acid Sequence; D053829:Amyloid Precursor Protein Secretases / Q000378:metabolism / Q000502:physiology*; D016229:Amyloid beta-Peptides / Q000378:metabolism*; D006801:Humans; D008562:Membrane Glycoproteins / Q000378:metabolism; D008854:Microscopy, Electron; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D051880:Receptors, Notch / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D014867:Water / Q000737:chemistry
chemical_list: D016229:Amyloid beta-Peptides; D008562:Membrane Glycoproteins; D051880:Receptors, Notch; C413604:nicastrin protein; D014867:Water; D053829:Amyloid Precursor Protein Secretases