Characterisation of an epitope specific to the neuron-specific isoform of human enolase recognised by a monoclonal antibody raised against a synthetic peptide corresponding to the C-terminus of β/A4-protein

Abstract

Antibodies to synthetic peptides corresponding to different regions of β/A4-protein recognize deposits of amyloid in the brains of patients with Alzheimer's disease. Down's syndrome cases and in the normal ageing brain. We have prepared a monoclonal antibody, mAb 22.212, raised against a synthetic C-terminal peptide of β/A4 protein (residues 28–40) which labelled senile plaques in Alzheimer's disease after proteolytic treatment of tissue sections. In addition to recognising synthetic β/A4-peptides that include the C-terminal residues 28–42, the mAb 22.212 was found to cross-react with a soluble, 47 kDa protein found in brain homogenates. This protein was shown, by amino acid sequence analysis and immunoassay, to be neuron-specific enolase (NSE). The mAb 22.212 did not recognize the non-neuronal enolase (NNE) or muscle-specific enolase (MSE) isoforms and its epitope was mapped to a short stretch of amino-acids unique to NSE, near the C-terminus. The cross-reactive NSE epitope is sited between residues 402–423 in NSE and shows no common sequence with β/A4, perharps suggesting that it is a conformational epitope. The significance and applications of these findings are discussed.