MOLECULAR-CLONING OF CDNA-ENCODING AN UNRECOGNIZED COMPONENT OF AMYLOID IN ALZHEIMER-DISEASE

A neuropathological hallmark of Alzheimer disease (AD) is a widespread amyloid deposition. We analyzed the entire amino acid sequences in an amyloid preparation and found, in addition to the major beta/A4-prote in (Abeta) fragment, two unknown peptides. We raised antibodies agains t synthetic peptides using subsequences of these peptides. These antib odies immunostained amyloid in neuritic and diffuse plaques as well as vascular amyloid. Electron microscopic analysis demonstrated that the immunostaining was localized on amyloid fibrils. We have isolated an apparently full-length cDNA encoding a 140-amino-acid protein within w hich two previously unreported amyloid sequences are encoded in tandem in the most hydrophobic domain. We tentatively named this 35-amino ac id peptide NAC (non-Abeta component of AD amyloid) and its precursor N ACP. NAC is the second component, after Abeta, identified chemically i n the purified AD amyloid preparation. Secondary structure predictions indicate that the NAC peptide sequence has a strong tendency to form beta-structures consistent with its association with amyloid. NACP is detected as a M(r) 19,000 protein in the cytosolic fraction of brain h omogenates and comigrates on immunoblots with NACP synthesized in Esch erichia coli from NACP cDNA. NACP mRNA is expressed principally in bra in but is also expressed in low concentrations in all tissues examined except in liver, suggesting its ubiquitous and brain-specific functio ns. The availability of the cDNA encoding full-length NACP should help to elucidate the mechanisms of amyloidosis in AD.