Biology subjects

Mapa, K.

Publications and source records attributed to Mapa, K..

6 recordsLinked to original sources

bioRxiv2025

The N-terminal Segment of the Human ANKZF1 negatively regulates its internal mitochondrial targeting signal to prevent its mitochondrial localization

ANKZF1, the human orthologue of yeast Vms1, is a multi-domain cytosolic protein. Occasionally, the protein is also found in mitochondria, although the reason for its mitochondrial localization and the mechanism of its mitochondrial targeting remains unclear. Despite the absence of any predicted Mitochondrial Targeting Sequence or Domain (MTS/MTD) in the protein, ANKZF1 possesses multiple internal Matrix-targeting sequence-like sequences (iMTS-Ls). In this study, we show that ANKZF1s N-terminal 73 residues negatively regulate its mitochondrial targeting. Interestingly, 1-72-ANKZF1 peptide hinders the mitochondrial targeting of {Delta}73-ANKZF1 upon co-expression. Using a series of truncation mutants of ANKZF1, we further show that iMTS-Ls constituted by residues 231-240 of ANKZF1 is indispensable for its mitochondrial localization. The sequence of 231-240 residues is extremely conserved across different organisms, indicating the importance of this segment for conditional mitochondrial targeting of the protein. Importantly, 231-324 residues containing two consecutive predicted iMTS-Ls constitute an independent mitochondrial signal sequence and can target Green Fluorescent Protein (GFP) to mitochondria when fused to N-terminus. Further, by Molecular Dynamic simulation, we show that the deletion of N-terminal 74 amino acids of ANKZF1 leads to a massive structural rearrangement within the protein leading to the opening of its C-terminal part and solvent exposure of the 231-240 residues. We posit that these structural rearrangements and exposure of the internal mitochondrial targeting sequence in the absence of N-terminal segment of ANKZF1 leads to its mitochondrial translocation.

cell biology↗

bioRxiv2024

ANKZF1 helps to eliminate the stress-damaged mitochondria by LC3-mediated mitophagy

Mitochondria, the double membrane-bound organelles of endosymbiotic origin, are crucial centers for cellular energy production and several essential metabolic pathways. Recent studies reveal that mitochondria become dysfunctional following numerous cellular stresses, and during pathologies, demanding an extensive investigation of mitochondrial turnover mechanisms. Apart from the specific response pathways to tackle different stresses, mitophagy or degradation of mitochondria by autophagy is a critical quality control mechanism that clears irreversibly damaged mitochondria. Mitophagy is majorly executed either by receptor-mediated or PINK1-Parkin-dependent pathways. Here, we show that the human orthologue of yeast Vms1, ANKZF1, participates in PINK-Parkin-mediated mitophagy. We show that ANKZF1 is extensively recruited to damaged mitochondria along with Parkin during mitochondrial proteotoxic stress induced by the expression of a single misfolded/aggregated protein or during uncoupler-induced membrane depolarization. Importantly, ANKZF1 recruitment to damaged mitochondria is significantly enhanced in the presence of Parkin, and ANKZF1 physically interacts with Parkin and LC3 during mitochondrial proteotoxic or depolarization stresses. ANKZF1 harbors six putative LC3-interacting regions (LIRs), LIR4 present at residues 333-336 is particularly important for ANKZF1-LC3 interaction. Furthermore, we show that ANKZF1 knockout cells are compromised in clearing stress-damaged mitochondria by mitophagy, indicating an important role of ANKZF1 in mitochondrial turnover during stress. In summary, we show a new role of ANKZF1 in eliminating the stress-damaged mitochondria, reiterating the mito-protective role of Vms1/ANKZF1 during mitochondrial stresses.

cell biology↗

bioRxiv2023

Sse1, Hsp110 chaperone of yeast, controls the cellular fate during Endoplasmic Reticulum-stress

Sse1 is a cytosolic Hsp110 molecular chaperone of yeast, Saccharomyces cerevisiae. Its multifaceted roles in cellular protein homeostasis as Nucleotide Exchange Factor (NEF), as protein-disaggregase and as a Chaperone linked to Protein Synthesis (CLIPS), are well documented. In the currently study, we show that SSE1 genetically interacts with IRE1 and HAC1, the Endoplasmic Reticulum-Unfolded Protein Response (ER-UPR) sensors implicating its role in ER protein homeostasis. Interestingly, absence of this chaperone imparts unusual resistance to tunicamycin-induced ER stress which depends on the intact Ire1-Hac1 mediated ER-UPR signalling. Furthermore, cells lacking SSE1 show ER-stress-responsive inefficient reorganization of translating ribosomes from polysomes to monosomes and increased monosome content that drive uninterrupted protein translation. In consequence, the kinetics of ER-UPR is starkly different in sse1{Delta} strain where we show that stress response induction and restoration of homeostasis is prominently faster in contrast to the wildtype (WT) cells. Importantly, Sse1 plays a critical role in controlling the ER-stress mediated cell division arrest which is escaped in sse1{Delta} strain during chronic tunicamycin stress. Consequently, sse1{Delta} strain shows significantly higher cell viability in comparison to WT yeast, following short-term as well as long-term tunicamycin stress. In summary, we demonstrate a new role of Sse1 in ER protein homeostasis where the chaperone genetically interacts with ER-UPR pathway, controls the protein translation during ER stress and the kinetics of ER-UPR. More importantly, we show the crtical role of Sse1 in regulating the ER-stress-induced cell division arrest and cell death during global ER stress by tunicamycin. Author SummarySse1 is a cytosolic Hsp110 molecular chaperone of yeast, Saccharomyces cerevisiae. It performs various functions as Nucleotide Exchange Factor (NEF), as a protein-disaggregase and as a Chaperone linked to Protein Synthesis (CLIPS) to maintain a healthy proteome in the cytosol. In the present study, we show that SSE1 is a critical player to maintain Endoplasmic Reticulum (ER) protein homeostasis. We report that SSE1 genetically interacts with the ER-Unfolded Protein Response (ER-UPR) sensors, IRE1 and HAC1. In absence of SSE1, yeast cells gain unusual fitness to tunicamycin (Tm)-induced ER stress which depends on the functional Ire1-Hac1 mediated ER-UPR signalling. Furthermore, Sse1 controls the ribosomal organization during tunicamycin-induced ER-stress and in absence of the chaperone the amount of polysomes and monosmes are high leading to uninterrupted protein translation during ER stress. Consequently, sse1{Delta} strain exhibits starkly different ER-UPR kinetics compared to wildtype (WT) cells. Importantly, our data reveal that cell division arrest and cell death due to Tm-induced ER-stress is critically controlled by Sse1.

cell biology↗

bioRxiv2020

Localized Proteotoxic Stress in Mitochondrial Intermembrane Space and Matrix Elicits Sub-compartment Specific Response Pathways Governed by Unique Modulators

The double-membrane-bound architecture of mitochondria, essential for ATP production, sub-divides the organelle into inter-membrane space (IMS) and matrix. IMS and matrix possess contrasting oxido-reductive environments and distinct protein quality control (PQC) machineries resulting different protein folding environments. To understand the nature of stress response elicited by equivalent proteotoxic stress to sub-mitochondrial compartments, we fused well-described bipartite or matrix-targeting signal sequences to misfolding and aggregation-prone stressor proteins to target and impart stress to yeast mitochondrial IMS or matrix. We show, mitochondrial proteotoxicity leads to growth arrest of yeast cells of varying degrees depending on nature of stressor proteins and the intra-mitochondrial location of stress. Next, using transcriptomics and proteomics, we report a comprehensive stress response elicited by two types of targeting signal-fused stressor proteins. Among global responses by mitochondria-targeted stressors by both types of signal sequences, an adaptive response of abrogated mitochondrial respiration and concomitant upregulation of glycolysis is uncovered. Beyond shared stress responses, specific signatures due to stress within mitochondrial sub-compartments are also revealed. We report that bipartite signal sequence-fused stressor proteins eliciting stress to IMS, leads to specific upregulation of IMS-chaperones and TOM complex components. In contrast, matrix-targeted stressors lead to specific upregulation of matrix-chaperones and cytosolic PQC components. Finally, by systematic genetic interaction using deletion strains of differentially upregulated genes, we found prominent modulatory role of TOM complex components during IMS-stress response. In contrast, VMS1 markedly modulates the stress response originated from matrix.

cell biology↗

bioRxiv2020

GroEL/ES Buffers Entropic Traps In Folding Pathway During Evolution Of A Model Substrate

The folding landscape of proteins can change during evolution with the accumulation of mutations that may introduce entropic or enthalpic barriers in the protein folding pathway, making it a possible substrate of molecular chaperones in vivo. Can the nature of such physical barriers of folding dictate the feasibility of chaperone-assistance? To address this, we have simulated the evolutionary step to chaperone-dependence keeping GroEL/ES as the target chaperone and GFP as a model protein in an unbiased screen. We find that the mutation conferring GroEL/ES dependence in vivo and in vitro encode an entropic trap in the folding pathway rescued by the chaperonin. Additionally, GroEL/ES can edit the formation of non-native contacts similar to DnaK/J/E machinery. However, this capability is not utilized by the substrates in vivo. As a consequence, GroEL/ES caters to buffer mutations that predominantly cause entropic traps, despite possessing the capacity to edit both enthalpic and entropic traps in the folding pathway of the substrate protein.

molecular biology↗

bioRxiv2017

Chaperone Network Based On Cellular Response Reveals The Non-Optimal Response To Perturbed Proteostasis

The proteostasis network (PN) comprises a plethora of proteins that are dedicated to aid in protein folding; some with over-lapping functions. Despite this, there are multiple pathophysiological states associated with depletion of chaperones. This is counter-intuitive assuming cells have the ability to re-program transcriptional outputs in accordance with its proteostasic limitations. To this effect, we have used S. cerevisiae to understand the route a cell takes as a response when challenged with different proteostasis impairments. Using 14 single deletion strains of genes of Protein Quality Control (PQC) system, we quantify their proteostasis impairment and the transcriptional response. In most cases cellular response was incapable of restoring proteostasis. The response did not activate proteostasis components or pathways that could complement the function of the missing PQC gene. Over-expression of alternate machineries, could restore part of the proteostasis defect in deletion strains. We posit that epistasis guided synthetic biology approaches may be helpful in realizing the true potential of the cellular chaperone machinery.

genetics↗