TPPP/p25: A New Unstructured Protein Hallmarking Synucleinopathies

There is increasing evidence that unfolded and misfolded proteins initiate a cascade of pathogenic protein-protein interactions that culminate in neuronal dysfunction. This is a multistep process which results in toxic protein aggregates; thus they are potent targets for development of early diagnosis and of drugs to improve therapies of conformational diseases. The hallmark proteins of these diseases such as Parkinson’s, Alzheimer’s or Huntington’s diseases, are α-synuclein, tau or mutant huntingtin, respectively, which do not have well-defined 3D structures and require protein partners to express their pathological functions. In this paper we review a new unstructured protein denoted Tubulin Polymerization Promoting Protein, TPPP/p25, from the discovery to its enrichment in human pathological inclusions characteristic for synucleinopathies with specific emphasis on its pursuits in single cells. There is a gappy area in the research of unfolded proteins referring to their structure-derived physiological and pathological functions. The studies of TPPP-homologous proteins at different levels of organization, molecular, cellular and tissue levels, rendered possible to reveal some TPPP/p25 specific structural and functional features, in addition to the general items for the role of the unfolded regions of the highly flexible proteins in their physiological and/or pathological functions.