Co-expression of nicastrin and presenilin rescues a loss of function mutant of APH-1.
gamma-Secretase is an intramembrane-cleaving aspartyl protease complex that mediates the final cleavage of beta-amyloid precursor protein to liberate the neurotoxic amyloid-beta peptide implicated in Alzheimer's disease. The four proteins presenilin (PS), nicastrin (NCT), APH-1, and PEN-2 are sufficient to reconstitute gamma-secretase activity in yeast. Although PS seems to contribute the catalytic core of the gamma-secretase complex, no distinct function could be attributed to the other components so far. In Caenorhabditis elegans, mutation of a glycine to an aspartic acid within a conserved GXXXG motif in the fourth transmembrane domain of APH-1 causes a loss of function phenotype. Surprisingly, we now found that the human homologue APH-1a carrying the equivalent mutation G122D is fully active in yeast co-expressing PS1, NCT, and PEN-2. To address this discrepancy, we expressed APH-1a G122D in HEK293 cells. As reported previously, overexpressed APH-1a G122D was not incorporated into the gamma-secretase complex. Separate overexpression of PS1, NCT, or PEN-2 together with APH-1a G122D allowed the formation of heterodimers lacking the other endogenous components. Only the combined overexpression of PS1 and NCT together with APH-1a G122D facilitated the formation of a fully active gamma-secretase complex. Under these conditions, APH-1a G122D supported the production of normal amounts of Abeta. We conclude that cooperative effects may stabilize a trim-eric complex of APH-1a G122D together with PS1 and NCT. Upon successful complex assembly, the GXXXG motif becomes dispensable for gamma-secretase activity.
Edbauer
Dieter
D
Adolf-Butenandt-Institute, Department of Biochemistry, Laboratory for Alzheimer's and Parkinson's Disease Research, Schillerstr. 44, Ludwig-Maximilians-University, 80336 Munich, Germany. edbauer@mit.edu
Kaether
Christoph
C
Steiner
Harald
H
Haass
Christian
C
D000483:Alleles; D053829:Amyloid Precursor Protein Secretases; D002460:Cell Line; D010450:Endopeptidases; D006801:Humans; D008562:Membrane Glycoproteins / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics*; D009154:Mutation; D010447:Peptide Hydrolases; D053764:Presenilin-1
D008562:Membrane Glycoproteins; D008565:Membrane Proteins; C508853:PSEN1 protein, human; D053764:Presenilin-1; C413604:nicastrin protein; C475154:APH1A protein, human; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D010447:Peptide Hydrolases