Interplay between Copper, Neprilysin, and N-Truncation of β-Amyloid

Sporadic Alzheimer's disease (AD) is associated with an inefficient clearance of the beta-amyloid (Afi) peptide from the central nervous system. The protein levels and activity of the Zn-dependent endopeptidase neprilysin (NEP) inversely correlate with brain A beta levels during aging and in AD. The present study considered the ability of Cu2+ ions to inhibit human recombinant NEP and the role for NEP in generating N-truncated A beta fragments with high-affinity Cu binding motifs that can prevent this inhibition. Divalent copper noncompetitively inhibited NEP (K-i = 1.0 mu M), while proteolysis of Afi yielded the soluble, A beta(4-9) fragment that can bind Cu' with femtomolar affinity at pH 7.4. This provides Afi4_9 with the potential to act as a Cu2+ carrier and to mediate its own production by preventing NEP inhibition. Enzyme inhibition at high Zn2+ concentrations (K, = 20 mu M) further suggests a mechanism for modulating NEP activity, A beta(4-9) production, and Cu2+ homeostasis.