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Protein Homeostasis Lab
Research Theme of the Group
Regulation of protein quality control in health and disease.
1.Elucidating the Stress response pathways of Mitochondrial Proteotoxic Stress in yeast, Saccharomyces cerevisiae
Mitochondrial dysfunction and loss of proteostasis have been designated as two major hallmarks of aging. Mitochondria, an organelle of endosymbiotic origin, has become critically dependent for its protein pool on the host cell nuclear genome despite harbouring its own DNA and complete protein synthesis apparatus. Moreover, the complex two-membrane boundary of the organelle make the whole process of protein import, sorting into intra-mitochondrial compartments and finally folding into functional native form, a mammoth task. Designated molecular chaperones belonging to various classes maintain the mitochondrial protein homeostasis (can be called as 'mitostasis') although the stress sensors and effectors to restore the homeostasis, still remain elusive. Using yeast, S. cerevisiae, as a model system, we have recently elucidated the sub-mitochondrial compartment (Inter-membrane Space or IMS and Mitochondrial Matrix) specific proteotoxic stress response using forward and reverse genetics (PMID 35500842). We extensively used various biochemical and biophysical assays to address the problem. Various next-gen technologies like RNA sequencing, quantitative proteomics are also employed to address the question, in collaboration with various institutes like CSIR-IGIB, CSIR-CCMB etc. Over and above the generalized response of mitochondrial proteotoxic stress, we have also have discovered specific modulators of IMS stress (TOM complex subunits, Msp1, Ubx2) and matrix (Vms1) stress.
2.Understanding the Stress response pathways of Mitochondrial Proteotoxic Stress in mammalian cells
Similar to yeast system, we have also made sub-mitochondrial compartment (Inter-membrane Space or IMS and Mitochondrial Matrix) specific proteotoxic stress models in mammalian cells. By extensively using imaging techniques coupled with biochemical techniques, we are currently deciphering the stress response pathways following mitochondrial proteotoxic stress, in mammalian cells.
3.Delineation of structure-functions of Hsp70/Hsp110 molecular chaperones
Hsp70s are ubiquitous molecular chaperones involved in plethora of cellular functions. The physiological roles of this group of chaperones are tightly regulated by its helpers, also known as co-chaperones and mainly achieved by allosteric communication between its two functional modules/domains. An important sub-class of Hsp70s, called Hsp110s (Hsp105 in mammals) has been shown to function as nucleotide exchange factors (NEFs) for Hsp70s. The most striking feature of Hsp110s are its structural similarity with Hs70s. Hsp110s are also modular proteins like Hsp70s and contain two functional domains, N-terminal nucleotide binding domains and C-terminal peptide binding domain connected by a short linker sequence. So far, no NEF of Hsp70s were found to contain such two domain structures. Apart from its co-chaperone functions, Hsp110s have been implicated as a key aggregation preventing factor in many neurodegenerative disorders and it has been shown to harbour individual chaperone function. We have recently shown the rationale of Hsp70-like two-domain structure of Hsp110s and presence of domain allostery in Hsp110 proteins (PMID: 31423733). Currently we are exploring the non-canonical chaperone functions of Hsp110 protein of yeast in greater details.
4. Deciphering the unique chaperone function of Human Hsp60 in maintaining mitochondrial proteostasis.
Hsp60 chaperone, a member of the Class I chaperonin family, is a key player in maintenance of protein homeostasis of mitochondrial matrix, the innermost and major hub of mitochondrial biochemical reactions. The importance of Hsp60 in intracellular processes is underscored by its essentiality for cell viability and by association of a number of genomic variations in the Hsp60 gene in various devastating diseases. Various single substitution mutations of the protein have been found to be the causative factor for severely debilitating neurological disorders like Hereditary Spastic Paraplegia and Hypomyelinating leukodystrophy (HMLs), although the molecular level understanding of pathogenesis of such diseases remain largely obscure. Mechanistic details of chaperonine pathway of bacterial Hsp60/10 is very well established, although the working hypothesis of the human counterpart remains elusive. We have recently shown the differences in chaperoning mechanism of eukaryotic Hsp60/10s from bacterial GroEL/ES system (PMID: 35486698). We are trying to understand how do the common variants of human hsp60 gene affects the functionality of the protein. To address the question, we extensively employ molecular biology and protein biochemistry methods.
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