Amyloid beta-protein precursor juxtamembrane domain regulates specificity of gamma-secretase-dependent cleavages.
Amyloid beta-protein (Abeta), the major component of cerebral plaques associated with Alzheimer disease, is derived from amyloid beta-protein precursor (APP) through sequential proteolytic cleavage involving beta- and gamma-secretase. The intramembrane cleavage of APP by gamma-secretase occurs at two major sites, gamma and epsilon, although the temporal and/or mechanistic relationships between these cleavages remain unknown. In our attempt to address this issue, we uncovered an important regulatory role for the APP luminal juxtamembrane domain. We demonstrated in cell-based assays that domain replacements in this region can greatly reduce secreted Abeta resulting from gamma-cleavage without affecting the epsilon-cleavage product. This Abeta reduction is likely due to impaired proteolysis at the gamma-cleavage site. Further analyses with site-directed mutagenesis identified two juxtamembrane residues, Lys-28 and Ser-26 (Abeta numbering), as the critical determinants for efficient intramembrane proteolysis at the gamma-site. Consistent with the growing evidence that epsilon-cleavage of APP precedes gamma-processing, longer Abeta species derived from the gamma-cleavage-deficient substrates were detected intracellularly. These results indicate that the luminal juxtamembrane region of APP is an important regulatory domain that modulates gamma-secretase-dependent intramembrane proteolysis, particularly in differentiating gamma- and epsilon-cleavages.
Ren
Zhao
Z
Elan Pharmaceuticals, Inc., South San Francisco, California 94080, USA.
Schenk
Dale
D
Basi
Guriqbal S
GS
Shapiro
I Paul
IP
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D053829:Amyloid Precursor Protein Secretases / Q000378:metabolism*; D016229:Amyloid beta-Peptides / Q000737:chemistry* / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D008239:Lysine / Q000737:chemistry; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000737:chemistry; D013997:Time Factors
D016229:Amyloid beta-Peptides; D012694:Serine; D053829:Amyloid Precursor Protein Secretases; D008239:Lysine