Biology subjects

Sunil, S.

Publications and source records attributed to Sunil, S..

5 recordsLinked to original sources

bioRxiv2022

Targeted photothrombotic stroke leads to disruptions in neurovascular coupling

Functional neuroimaging, which measures hemodynamic responses to brain activity, has great potential for monitoring stroke patients. However, the neurophysiological interpretations of these hemodynamic signals remain a challenge as the stroke is likely to alter both neural activity and neurovascular coupling. To address this challenge, we simultaneously captured neural activity, through fluorescence calcium imaging, and hemodynamics, through intrinsic optical signal imaging, during longitudinal stroke recovery. We found that photothrombotic stroke to somatosensory forelimb region altered neurovascular coupling in the acute phase (2 days and 1 week post-stroke) within the affected forelimb and peri-infarct regions. Neurovascular coupling was reestablished in the chronic phase (4 weeks post-stroke), and acute recovery of neurovascular coupling predicted sensorimotor function. Stroke also resulted in increases in the power of global brain oscillations, which showed distinct patterns between calcium and hemodynamics. Increased calcium excitability in the contralesional hemisphere was associated with increased intrahemispheric connectivity. Additionally, acute increases in hemodynamic oscillations were associated with improved sensorimotor outcomes. TeaserAcute ischemic stroke leads to neurovascular uncoupling and the extent of early recoupling predicts sensorimotor recovery.

physiology↗

bioRxiv2021

Zinc2+ ion inhibits SARS-CoV-2 main protease and viral replication in vitro.

Zinc deficiency is linked to poor prognosis in COVID-19 patients while clinical trials with Zinc demonstrate better clinical outcome. The molecular target and mechanistic details of anti-coronaviral activity of Zinc remain obscure. We show that ionic Zinc not only inhibits SARS-CoV-2 main protease (Mpro) with nanomolar affinity, but also viral replication. We present the first crystal structure of Mpro-Zn2+ complex at 1.9 [A] and provide the structural basis of viral replication inhibition. We show that Zn2+ coordinates with the catalytic dyad at the enzyme active site along with two previously unknown water molecules in a tetrahedral geometry to form a stable inhibited Mpro-Zn2+ complex. Further, natural ionophore quercetin increases the anti-viral potency of Zn2+. As the catalytic dyad is highly conserved across SARS-CoV, MERS-CoV and all variants of SARS-CoV-2, Zn2+ mediated inhibition of Mpro may have wider implications.

biochemistry↗

bioRxiv2021

Guidelines for obtaining an absolute blood flow index with laser speckle contrast imaging

Laser speckle contrast imaging (LSCI) is a technique broadly applied in research and clinical settings for full-field characterization of tissue perfusion. It is based on the analysis of speckle pattern contrast, which can be theoretically related to the decorrelation time - a quantitative measure of dynamics. A direct contrast to decorrelation time conversion, however, requires prior knowledge of specific parameters of the optical system and scattering media and thus is often impractical. For this reason, and because of the nature of some of the most common applications, LSCI is historically used to measure relative blood flow change. Over time, the belief that the absolute blood flow index measured with LSCI is not a reliable metric and thus should not be used has become more widespread. This belief has resulted from the use of LSCI to compare perfusion in different animal models and to obtain longitudinal blood flow index observations without proper consideration given to the stability of the measurement. Here, we aim to clarify the issues that give rise to variability in the repeatability of the quantitative blood flow index and to present guidelines on how to make robust absolute blood flow index measurements with conventional single-exposure LSCI. We also explain how to calibrate contrast to compare measurements from different systems and show examples of applications that are enabled by high repeatability.

bioengineering↗

bioRxiv2021

The plant immune receptors NRG1.1 and ADR1 are calcium influx channels

Plant nucleotide-binding leucine-rich repeat receptors (NLRs) regulate immunity and cell death. RPW8 domain-containing "helper" NLRs (RNLs) are required by many "sensor" NLRs. Our crystal structure of the RNL N REQUIREMENT GENE 1.1 (NRG1.1) N-terminal signaling domain resembled that of the resting state plant resistosome-forming HOPZ-ACTIVATED RESISTANCE 1 (ZAR1) and the animal MIXED-LINEAGE KINASE-LIKE (MLKL) cation channel. Active NRG1.1 oligomerized, was enriched in plasma membrane puncta and conferred cytoplasmic Ca2+ influx in plant and human HeLa cells. NRG1.1-dependent Ca2+ influx and cell death were sensitive to Ca2+ channel blockers. Ca2+ influx and cell death mediated by NRG1.1 and ACTIVATED DISEASE RESISTANCE 1 (ADR1), another RNL, required conserved negatively charged N-terminal residues. Thus, RNLs apparently form influx channels to directly regulate cytoplasmic [Ca2+] and consequent cell death. One Sentence SummaryA specific class of plant immune receptors function as calcium-permeable channels upon activation to induce cell death.

plant biology↗

bioRxiv2020

Coiled-coil and RPW8-type immune receptors function at the plasma membrane in a phospholipid dependent manner

Activation of intracellular nucleotide-binding leucine-rich repeat receptors (NLRs) results in immunity and a localized cell death response of infected cells. Cell death activity of many NLRs requires oligomerization and in some cases plasma membrane (PM) localization. However, the exact mechanisms underlying PM localization of NLRs lacking recognizable N- or C-terminal lipidation motifs or predicted transmembrane domains remains elusive. Here we show that the PM localization and stability of members of the RPW8-like coiled-coil (CCR) domain NLRs (RNLs) and a CC-type NLR (CNL) depend on the interaction with PM phospholipids. Depletion of phosphatidylinositol-4-phosphate (PI4P) from the PM led to a mislocalization of the analyzed NLRs and consequently inhibited their cell death activity. We further demonstrate activation-dependent self-association of cell death inducing RNLs. Our results provide new insights into the molecular mechanism of NLR PM localization and defines an important role of phospholipids for CNL and RNL activity during immunity.

plant biology↗