Functional aspects of cellular microcompartmentation in the development of neurodegeneration: mutation induced aberrant protein-protein associations.

Research in the last 10 years has revealed that the development of neurodegeneration is a multistep process during which one or few specific mutant protein species of altered conformation initiate aberrant protein-protein interactions resulting in aggregates forming plaques. This review focuses on the heteroassociations of the mutant proteins with subcellular structures, such as cytoskeleton, cell membranes or with glycolytic enzymes, which may be crucial in the initiation of neurodegeneration such as in Huntington's disease or Alzheimer's disease. Triosephosphate isomerase enzymopathy is a unique glycolytic enzyme deficiency coupled with neurodegeneration. We present data on the mutation induced misfolding process, which likely plays a crucial role in the enhanced associations of the enzyme with the truncated fragment of the isomerase, with the red cell membrane or with the microtubular network. On the basis of our recent clinical and experimental results obtained with two compound heterozygote Hungarian brothers it became obvious that the mutations alone are not sufficient to explain the development of the neurological sympthomes. This underscores the fact that the mutations alone are not enough for the development of the clinical phenotype of a disease.