Biology subjects

Basu, K.

Publications and source records attributed to Basu, K..

5 recordsLinked to original sources

bioRxiv2023

Phosphorylation of a Cleaved Tau Proteoform at a Single Residue Inhibits Binding to the E3 Ubiquitin Ligase, CHIP

Microtubule-associated protein tau (MAPT/tau) accumulates in a family of neurodegenerative diseases, including Alzheimers disease (AD). In disease, tau is aberrantly modified by post-translational modifications (PTMs), including hyper-phosphorylation. However, it is often unclear which of these PTMs contribute to taus accumulation or what mechanisms might be involved. To explore these questions, we focused on a cleaved proteoform of tau (tauC3), which selectively accumulates in AD and was recently shown to be degraded by its direct binding to the E3 ubiquitin ligase, CHIP. Here, we find that phosphorylation of tauC3 at a single residue, pS416, is sufficient to block its interaction with CHIP. A co-crystal structure of CHIP bound to the C-terminus of tauC3 revealed the mechanism of this clash and allowed design of a mutation (CHIPD134A) that partially restores binding and turnover of pS416 tauC3. We find that pS416 is produced by the known AD-associated kinase, MARK2/Par-1b, providing a potential link to disease. In further support of this idea, an antibody against pS416 co-localizes with tauC3 in degenerative neurons within the hippocampus of AD patients. Together, these studies suggest a discrete molecular mechanism for how phosphorylation at a specific site contributes to accumulation of an important tau proteoform.

biochemistry↗

bioRxiv2020

Dengue virus sustains viability of infected cells by counteracting apoptosis-mediated DNA breakage

NS1, a virotoxin, abundantly present in Dengue patients blood, is a major player behind disease patho-biogenesis including plasma leakage and damage to the liver. Despite the presence of NS1 in blood, Dengue is asymptomatic and self-limiting in [≥]80% Dengue virus (DV) infected people. We investigated this observation and found that plasmid-mediated NS1 expression and secretion in liver cells (Huh7) are sufficient to cause programmed cell death (apoptosis) and associated cellular DNA breakage. However, liver or kidney cell lines infected with DV and secreting equivalent amounts of NS1 didnt exhibit apoptotic DNA breakage. In fact, DV-infected cells showed better survival than cells in which only NS1 was transiently expressed by transfection. We also found that DV can even prevent chemical-induced apoptotic DNA damage in infected host cells. So, DV thwarts host antiviral defence i.e. apoptosis, by counteracting cellular DNA breakages and keeps the infected cells metabolically active to prolong virus replication.

microbiology↗

bioRxiv2020

Alternative Conformations and Motions Adopted by 30S Ribosomal Subunits Visualized by Cryo-Electron Microscopy.

It is only after recent advances in cryo-electron microscopy that is now possible to describe at high resolution structures of large macromolecules that do not crystalize. Purified 30S subunits interconvert between the "active" and "inactive" conformations. The active conformation was described by crystallography in the early 2000s, but the structure of the inactive form at high resolution remains unsolved. Here we used cryo-electron microscopy to obtain the structure of the inactive conformation of the 30S subunit to 3.6[A] resolution and study its motions. In the inactive conformation, three nucleotides at the 3 end of the 16S rRNA cause the region of helix 44 forming the decoding center to adopt an unlatched conformation and the 3 end of the 16S rRNA positions similarly to the mRNA during translation. Incubation of inactive 30S subunits at 42 {degrees}C reverts these structural changes. The position adopted by helix 44 dictates the most prominent motions of the 30S subunit. We found that extended exposures to low magnesium concentrations induces unfolding of large rRNA structural domains. The air-water interface to which ribosome subuints are exposed during sample preparation also peel off some ribosomal proteins. Overall this study provides new insights about the conformational space explored by the 30S ribosomal subunit when the ribosomal particles are free in solution.

molecular biology↗

bioRxiv2019

Tubulin Lattice in Cilia is in a Stressed Form Regulated by Microtubule Inner Proteins

Cilia, the hair-like protrusions that beat at high frequencies to propel a cell or move fluid around the cell, are composed of radially bundled doublet microtubules. The doublet microtubule is composed of a 13-protofilament A-tubule, a partial 10-protofilament B-tubule and microtubule inner proteins (MIPs) inside the tubulin lattice. In this study, we present the near-atomic resolution map of the Tetrahymena doublet microtubules. The map demonstrates that the network of microtubule inner proteins is weaving into the tubulin lattice, forming an inner sheath of proteins. In addition, we also obtain the tubulin lattice structure with missing MIPs by Sarkosyl treatment. In this structure, the tubulin lattice showed significant longitudinal compaction and lateral angle changes between protofilaments. These results are evidence that the binding of MIPs directly affects and stabilizes the tubulin lattice. It is also suggested that the doublet microtubule is an intrinsically stressed filament and this stress could be exploited in the regulation of ciliary waveforms.

biophysics↗

bioRxiv2019

Role of Era in Assembly and Homeostasis of the Ribosomal Small Subunit

To reveal the role of the essential protein Era in the assembly of the 30S ribosomal subunit, we analyzed assembly intermediates that accumulated in Era-depleted Escherichia coli cells using quantitative mass spectrometry, cryo-electron microscopy and in-cell footprinting. Our combined approach allowed for visualization of the small subunit as it assembled and revealed that with the exception of key helices in the platform domain, all other 16S rRNA domains were able to fold even in the absence of Era. Notably, the maturing particles did not stall while waiting for the platform domain to mature and instead re-routed their folding pathway to enable concerted maturation of other structural motifs spanning multiple rRNA domains. We also found that binding of Era to the mature 30S subunit destabilized helix 44 and the decoding center preventing binding of YjeQ, another assembly factor. This work establishes Eras role in ribosome assembly and suggests new roles in maintaining ribosome homeostasis.

molecular biology↗