Immunoaffinity chromatographic purification of amyloid-related proteins from Alzheimer's disease brain tissue

We describe the preparation and characterisation of an immunoaffinity column of immobilised monoclonal antibody 1G10/2/3 which was raised against a synthetic peptide representing residues 8-17 of the A4 amyloid protein (or beta-protein) of Alzheimer's disease (AD). In previous work we have shown that this antibody reacts in formalin-fixed, paraffin-embedded tissue sections with plaque cores, plaque periphery and cerebrovascular amyloid of AD. We have used the column in the immunoaffinity isolation from extracts prepared from AD brain tissue of a protein with an apparent molecular weight of 31,000; this protein is reactive with 1G10/2/3 in Western blots. The same protein is also present, but at lower level, in normal control brain tissue. Possible relationships of this protein to the predicted structures for full-length A4-precursors are discussed. However, in view of the preliminary nature of the observations and potential problems relating to proteolysis occurring post-mortem or during the extraction process, firm conclusions cannot be drawn about any role for this molecule in the normal functioning of A4-precursors or in the conversion of A4-precursor to the deposits of A4 seen in AD brain. Nevertheless, we conclude that we are seeing a stable but truncated form of A4-precursor and it will be of interest to see if further studies can clarify the possible relevance of the protein to normal or pathological processes in human brain tissue.