STRUCTURAL INVESTIGATIONS OF THE CDK5:P35 COMPLEX

This research plan concerns the functional mechanisms of a protein complex, whose deregulation is strongly correlated with the development of Alzheimer’s Disease. Our complex is formed by two proteins, known as CDK5 and p35. It exists exclusively in neurons of the central nervous system. CDK5 (for Cyclin-Dependent Kinase 5) is an enzyme, whose activity consists in the addition of a phosphate group onto a target protein substrate. This process is known as phosphorylation. Usually, it acts as a trigger that modulated the function of the protein substrate. The physiological consequences of phosphorylation can be particularly relevant for a cell. p35, on the other hand, acts as an activator of CDK5, and its presence is absolutely required for CDK5 function. Recent studies showed that conditions that are stressful for a cell, such as oxygen deprivation, result in the processing of p35 to a protein of reduced size (p25) through the action of a protease, a molecular scissors. p25 retains the ability of activating CDK5. Relative to p35, however, p25 shows increased stability, and it accumulates in the cell. This ultimately results in an increase of CDK5 activity. This deregulated and unnecessary activity of CDK5 has profoundly toxic effect for the neuronal cell. Eventually, neurons die as an effect of this hyper-activation: indeed, cellular death is one of the clearest manifestations of Alzheimer’s Disease. Our goal is to comprehend the molecular bases behind the malfunction of the CDK5:p25 complex. The goal of our studies is the characterisation of the reciprocal distribution of the atoms that constitute this complex. To this end, we use a rather sophisticated form of microscopy, known as X-ray crystallography. Using this approach, we hope to be able to design selective inhibitors of CDK5, which would allow to block its function under conditions that lead to its deregulation.