Biology subjects

Immadisetty, K.

Publications and source records attributed to Immadisetty, K..

7 recordsLinked to original sources

bioRxiv2024

Rapid metabolic regulation of a novel arginine methylation of KCa3.1 attenuates T cell exhaustion.

T cell receptor (TCR) engagement initiates the activation process, and this signaling event is regulated in multifaceted ways. Nutrient availability in the immediate niche is one such mode of regulation1-3. Here, we investigated how the availability of an essential amino acid methionine (Met) and TCR signaling might interplay in the earliest events of T cell activation to affect subsequent T cell fate and function. We found that limiting Met during only the initial 30 minutes of CD8+ T cell activation increased Ca2+ influx, Ca2+-mediated NFAT1 (Nfatc2) activation, NFAT1 promoter occupancy, and T cell exhaustion. We identified changes in the protein arginine methylome during the initial 30 min of TCR engagement and discovered a novel arginine methylation of a Ca2+-activated potassium transporter, KCa3.1, which regulates Ca2+-mediated NFAT1 signaling to ensure optimal activation. Ablation of arginine methylation in KCa3.1 led to increased NFAT1 activation, rendering T cells dysfunctional in murine tumour and infection models. Furthermore, acute Met supplementation at early stages reduced nuclear NFAT1 in tumour-infiltrating T cells and augmented their anti-tumour activity. Our findings identify a metabolic event occurring early after T cell activation that influences the subsequent fate of the cell.

immunology↗

bioRxiv2022

Importance of AB domain in parvalbumins' calcium binding affinity

1Members of the parvalbumin (PV) family of calcium binding proteins are found in a variety of vertebrates, where can they influence neural functions, muscle contraction and immune responses. It was reported that the -parvalbumin (PV)s AB domain comprising two -helices, dramatically increases the proteins calcium (Ca2+) affinity by {approx}10 kcal/mol. To understand the structural basis of this effect, we conducted all-atom molecular dynamics (MD) simulations of WT PV and truncated -parvalbumin ({Delta}PV) constructs. Additionally, we also examined the binding of magnesium (Mg2+) to these isoforms, which is much weaker than Ca2+ (Mg2+ actually does not bind to the {Delta}PV). Our key finding is that reorganization energies (RE) assessed using molecular mechanics generalized Born approximation (MM/GBSA) correctly rank-order the variants according to their published Ca2+ and Mg2+ affinities. The [Formula] of the {Delta}PV compared to the wild-type (WT) is 415.57{+/-}0.55 kcal/mol, indicating that forming a holo state of {Delta}PV in the presence of Ca2+ incurs a greater reorganization penalty than the WT. This is consistent with the {Delta}PV exhibiting lesser Ca2+ affinity than the WT ({approx}9.5 kcal/mol). Similar trend was observed for Mg2+ bound variants as well. Further, we screened for metrics such as oxygen coordination of EF hand residues with ions and found that the total oxygen coordination number (16 vs. 12 in WT:Ca2+ and {Delta}PV:Ca2+) correlate with the reported ion affinities (-22 vs. -12.6 kcal/mol in WT:Ca2+ and {Delta}PV:Ca2+), which indicates that AB domain is required for the protein to coordinate with maximal efficiency with the binding ions. To our surprise, no significant differences were observed between the Mg2+ bound WT and {Delta}PV isoforms. Additionally, we have screened for factors such as total number of waters, hydrogen bonds, protein helicity and {beta}-content for the entire protein, which enables us to understand the impact of lack of AB domain on the entire structure and not just binding sites. Our data indicate that AB improves the overall helicity ({approx}5%) in apo as well as holo forms. Particularly, AB increases -helicity in the D-helix residues (i.e., 60-65) upon ion binding by {approx}35% (90% vs. 55% in the Ca2+ bound WT and {Delta}PV, 60% vs. 20% in the Mg2+ bound WT and {Delta}PV), which likely contributes to high Ca2+ binding affinity. On the contrary, no significant effect on the overall {beta}-content was observed. Similarly, increased dehydration ({approx}50) and increase in total number of hydrogen bonds ({approx}7) were observed upon ion binding in both the WT and {Delta}PV systems, however, no significant differences were observed between the WT and {Delta}PV variants and also between Ca2+ and Mg2+ isoforms. We speculate that this is due to the partially folded apo state that was captured in our MD simulations, which might not be physiologically relevant as suggested by NMR experiments [1]. Also, we have identified seven different interactions that might play a key role in binding the AB domain with the CDEF helices, particularly the D22(AB)-S78(CDEF) hydrogen bond. Overall, this study indicates that local (i.e., the EF hands) as well as global factors play a role in improved ion binding due to AB domain.

physiology↗

bioRxiv2022

An Investigation of the YidC-Mediated Membrane Insertion of Pf3 Coat Protein Using Molecular Dynamics Simulations

YidC is a membrane protein that facilitates the insertion of newly synthesized proteins into lipid membranes. Through YidC, proteins are inserted into the lipid bilayer via the SecYEG-dependent complex. Additionally, YidC functions as a chaperone in protein folding processes. Several studies have provided evidence of its independent insertion mechanism. However, the mechanistic details of the YidC independent protein insertion mechanism remain elusive at the molecular level. This study elucidates the insertion mechanism of YidC at an atomic level through a combination of equilibrium and non-equilibrium molecular dynamics (MD) simulations. Different docking models of YidC-Pf3 in the lipid bilayer were built in this study to better understand the insertion mechanism. To conduct a complete investigation of the conformational difference between the two docking models developed, we used classical molecular dynamics simulations supplemented with a non-equilibrium technique. Our findings indicate that the YidC transmembrane (TM) groove is essential for this high-affinity interaction and that the hydrophilic nature of the YidC groove plays an important role in protein transport across the cytoplasmic membrane bilayer to the periplasmic side. At different stages of the insertion process, conformational changes in YidCs TM domain and membrane core have a mechanistic effect on the Pf3 coat. Furthermore, during the insertion phase, the hydration and dehydration of the YidCs hydrophilic groove are critical. These demonstrate that Pf3 interactions with the membrane and YidC vary in different conformational states during the insertion process. Finally, this extensive study directly confirms that YidC functions as an independent insertase.

biophysics↗

bioRxiv2020

Structural determinants of calcium binding beyond the EF-hand binding site: A study of alpha parvalbumins

1Parvalbumin (PV) is a calcium binding protein expressed in humans, fish and avian species. In these organisms, the calcium (Ca2+) affinities of specific PV isoforms can vary by orders of magnitude. Despite the availability of high resolution structural data for many PV isoforms, the structural bases for how such proteins confer widely-varying divalent Ca2+ affinities and selectivities against common ions like magnesium (Mg2+) has been difficult to rationalize. We therefore conducted molecular simulations of several -pavalbumin (-parvalbumin (PV)) constructs with Ca2+ affinities in the micromolar to nanomolar ranges to identify properties of conformations that contribute to their wide-ranging binding constants and selectivities against Mg2+. Specifically, we examined a D94S/G98E construct with a reported lower Ca2+ affinity ({approx} -18.2 kcal/mol) relative to the WT ({approx} -22 kcal/mol), an S55D/E59D variant with enhanced affinity ({approx} -24 kcal/mol), and a truncated variant of PV with weak affinity ({approx} -12.6 kcal/mol). We performed molecular dynamics simulations of these constructs and assessed their Ca2+ and Mg2+ binding properties using scores from molecular mechanics generalized Born approximation (MM/GBSA), ion/oxygen coordination patterns and thermodynamics via mean spherical approximation (MSA) theory, as well as via metrics of protein structure and hydration. Our key findings are that although MM/GBSA and MSA scores successfully rank-ordered the variants according to their previously-published affinities and Mg2+ selectivity, importantly, properties of Ca2+ loops in CBPs such as coordination, and charge are alone insufficient to rationalize their binding properties. Rather, Ca2+ affinity and selectivity against Mg2+ are emergent properties stemming from both local effects within the proteins ion binding sites as well as non-local contributions from protein folding and solubility. Our findings broaden our understanding of the molecular bases governing PV ion binding that are likely shared by many Ca2+ binding proteins.

biophysics↗

bioRxiv2019

Conformational Transition Pathways in Major Facilitator Superfamily Transporters

AbstractThe major facilitator superfamily (MFS) of transporters contains three classes of membrane transporters: symporters, uniporters, and antiporters. Despite utilizing a variety of transport methods, MFS transporters are believed to undergo similar con-formational changes within their distinct transport cycles. Although the similarities regarding conformational changes between the classes of MFS transporters are note-worthy, the differences are also valuable because they may explain the distinct functions of the classes within the MFS. Here, we have performed a variety of equilibrium and non-equilibrium all-atom molecular dynamics (MD) simulations of the bacterial proton-coupled oligopeptide transporter (GkPOT) and the human glucose transporter 1 (GluT1). To compare the similarities and differences of the conformational dynamics found within the three different classes of transporters we have also referenced previous simulations involving the glycerol-3-phosphate (GlpT) transporter. All of the proteins discussed here were simulated in the apo state in explicit membrane environments. Our results suggest a very similar conformational transition for all transporter types involving interbundle salt-bridge formation/disruption coupled with the orientation changes of transmembrane (TM) helices, specifically H1/H7 and H5/H11, resulting in an alternation in the accessibility of water at the cyto- and periplasmic gates.

biophysics↗

bioRxiv2019

Elucidating the Molecular Basis of pH Activation of an Engineered Mechanosensitive Channel

Mechanosensitive (MS) channels detect and respond to changes in the pressure profile of cellular membranes and transduce the mechanical energy into electrical and/or chemical signals. However, by re-engineering the MS channels, chemical signals such as pH change can trigger the activation of some MS channels. This paper elucidate the activation mechanism of an engineered MS channel of large conductance (MscL) at an atomic level through a combination of equilibrium, non-equilibrium, biased, and unbiased molecular dynamics (MD) simulations for the first time. Comparing the wild-type and engineered MscL activation processes at an atomic level suggests that the two systems are likely to be associated with different active states and different transition pathways. These findings indicate that (1) periplasmic loops play a key role in the activation process of MscL, (2) the loss of various hydrogen bonds and salt bridge interactions in the engineered MscL channel causes the spontaneous opening of the channel, and (3) the most significant interactions lost during the activation process are those between the transmembrane (TM) helices 1 and 2 (TM1 and TM2) in engineered MscL channel. In this research, the orientation-based biasing approach for producing and optimizing an open MscL model is a promising way to characterize unknown protein functional states and to research the activation processes in ion channels. String method with swarms of trajectories (SMwST) was used to identify the optimal transition pathway and elucidate the activation mechanism of the engineered MscL. Finally, the free energy profile of engineered MscL associated with the activation process using a novel along-the-path free energy calculation approach is constructed. This work paves the way for a computational framework for the studies aimed at designing pH-triggered channel-functionalized drug delivery liposomes.

biophysics↗

bioRxiv2019

The Role of a Crystallographically Unresolved Cytoplasmic Loop in Stabilizing the Bacterial Membrane Insertase YidC2

YidC, a bacterial member of the YidC/Alb3/Oxa1 insertase family, mediates membrane protein assembly and insertion. Cytoplasmic loops are known to have functional significance in membrane proteins such as YidC. Employing microsecond-level molecular dynamics (MD) simulations, we show that the crystallographically unresolved C2 loop plays a crucial role in the structural dynamics of Bacillus halodurans YidC2. We have modeled the C2 loop and used allatom MD simulations to investigate the structural dynamics of YidC2 in its apo form, both with and without the C2 loop. The C2 loop was found to stabilize the entire protein and particularly the C1 region. C2 was also found to stabilize the alpha-helical character of the C-terminal region. Interestingly, the highly polar or charged lipid head groups of the simulated membranes were found to interact with and stabilize the C2 loop. These findings demonstrate that the crystallographically unresolved loops of membrane proteins could be important for the stabilization of the protein despite the apparent lack of structure, which could be due to the absence of the relevant lipids to stabilize them in crystallographic conditions.

biophysics↗