We study molecular mechanisms underlying human disease and focusing at cellular signaling networks. A particular emphasis is given to the discovery and development of new chemical tools for regulating protein kinases- key elements in signal transduction networks. We employ multidisciplinary research platforms from in vitro assays, computational analyses, and animal models to decipher signaling components that contribute to molecular pathogenesis, and to identify and design bioactive agents as future therapies. Our goal is to develop new therapeutics for diverse pathological disorders including diabetes, neurodegenerative disorders and cancer.
Research Projects in Our Laboratory:
- Development of systematic platform for development of protein kinase inhibitors.
- Design bioactive molecules that function as substrate competitive inhibitors for protein kinases.
- Study the role of autophagy and lysosome network in neurodegenerative disorders and cancer.
- Study evolutionary perspective of protein kinases as a unique tool for novel drug design.
Dysregulation of GSK-3 activity is believed to play a key role in the pathogenesis of CNS disorders. GSK-3 and its downstream pathways were shown to be tightly linked with signaling pathways regulating synaptic modulation, neuroprotection and neuroplasticity. Of particular relevance to neurodegenarative disorders, GSK-3 binds and / or phosphoryltes tau, presenilin-1, and collapsin response mediator protein, CRMP2, proteins that are implicated in the etiology of Alzheimer’s disease. Specifically, GSK-3 phosphorylates tau in most serine and threonine residues which are hyperphosphorylated in PHF (paired helical filament) in brains of Alzheimer’s patients. Subsequently, the phosphorylation of CRMP2 by GSK-3 affects neuroplasticity and axon grwoth. In addition, GSK-3 activity contributes to the production of Aβ peptide, the principal protein component of amyloid plaques, the hallmark of Alzheimer’s disease pathology. Furthermore, recent work suggested a mechanistic link between amyloid signaling and tauopathy via activation of GSK-3.
The GSK-3 inhibitors are useful tool in treating pathologies. Our laboratory develop specific GSK-3 inhibitors that are substrate competitive inhibitors, in contrast to other protein kinase inhibitors available that are ATP competitive inhibitors. Our strategy is based on understanding of how the enzyme recognizes and interacts with its substrates, and combines biochemical and computational analyses. Accordingly, we developed a novel class of substrate-competitive peptide inhibitors, headed by the compound “L803-mts”. In vivo inhibition of GSK-3 by L803-mts demonstrated its therapeutic benefits in diabetic, depressive behavior, and Alzheimer’s models.
- Research of signaling pathways of GSK-3 in neurodegenerative models.
- Structure/function analyses of GSK-3 iszoymes- at bioinfomatic and evolutionary perspectives.
- Design and develop new selective GSK-3 inhibitors, followed by testing in novel biological systems.
Mammalian GSK-3 exists as two isozymes, α and β, encoded by two different genes. We found that unlike other vertebrates, the GSK-3α gene is missing in birds. The α and β isozymes split from a common precursor approximately at the time of emergence of vertebrates. Although both GSK-3α and β genes are present and highly conserved in fish, amphibians, reptiles and mammals, the GSK-3α gene is missing from the genomes and transcriptomes of avian species indicating that the GSK-3α gene was lost after the split of ancestral birds from reptilians. Additionally we found that unlike other substrates of GSK-3, lack of GSK-3α resulted in a robust reduction in tau phosphorylation in the adult bird brain.
The protein kinase super family accounts for nearly 2% of the genes in the human genome and codes for about 545 kinases. The eukaryotic protein kinases are subdivided into three classes: two major classes, the serine/threonine and the tyrosine kinases, and one small class of dual specific kinase (serine/threonine and tyrosine). The classes share extensive sequence and structure homologies. The catalytic domains are typically characterized by a small N-terminal lobe that contains a glycine-rich loop (P-loop) for ATP binding and a larger C-terminal domain that contains a conserved activation loop (also called ‘T-loop’ or activation segment). ATP and substrates bind in the cleft between the two lobes. ATP is bound in a hydrophobic pocket, whereas substrates bind along the cleft and interact with a set of conserved residues that catalyze phosphorylation.
The substrate specificity of protein kinases typically depends on the primary amino acid sequences immediately flanking the site of phosphorylation, called the ‘consensus sequence’. The numbers and types of interactions with residues surrounding the phosphorylation site vary considerably among kinases, reflecting differences in sequence specificity. Protein kinase families are thus classified into basophilic, acedophilic and proline-directed kinases. The first group, which includes kinases such as PKA, PKB and PKC, prefers positively charged residues within the recognition motif. The consensus sequences of acidophilic group kinases, like casein kinase1/2, have acidic residues near the phosphorylation site. The largest family is the proline-directed kinases (MAPK’s, CDK’s, GSK-3) and the recognition motifs of these kinases all include proline.
Although all ‘classical’ protein kinases share a common catalytic fold, these proteins show remarkable diversity in their substrate specificity and signal transmission. This is mainly attributed to additional elements, such as distinct regions located outside the catalytic core, regulatory domains, or adaptor molecules that can directly affect the interaction with substrates or other components within the signaling network.