Now showing 1 - 10 of 10
  • Placeholder Image
    Publication
    Molecular Basis of Differential Stability and Temperature Sensitivity of ZIKA versus Dengue Virus Protein Shells
    (01-12-2020)
    Pindi, Chinmai
    ;
    Chirasani, Venkat R.
    ;
    Rahman, Mohammad Homaidur
    ;
    Ahsan, Mohd
    ;
    Revanasiddappa, Prasanna D.
    ;
    Rapid spread of ZIKA virus (ZIKV) and its association with severe birth defects have raised worldwide concern. Recent studies have shown that ZIKV retains its infectivity and remains structurally stable at temperatures up to 40 °C, unlike dengue and other flaviviruses. In spite of recent cryo-EM structures that showed similar architecture of ZIKA and dengue virus (DENV) E protein shells, little is known that makes ZIKV so temperature insensitive. Here, we attempt to unravel the molecular basis of greater thermal stability of ZIKV over DENV2 by executing atomistic molecular dynamics (MD) simulations on the viral E protein shells at 37 °C. Our results suggest that ZIKA E protein shell retains its structural integrity through stronger inter-raft communications facilitated by a series of electrostatic and H-bonding interactions among multiple inter-raft residues. In comparison, the DENV2 E protein shell surface was loosly packed that exhibited holes at all 3-fold vertices, in close agreement with another EM structure solved at 37 °C. The residue-level information obtained from our study could pave way for designing small molecule inhibitors and specific antibodies to inhibit ZIKV E protein assembly and membrane fusion.
  • Placeholder Image
    Publication
    Functional Gly297Ser Variant of the Physiological Dysglycemic Peptide Pancreastatin Is a Novel Risk Factor for Cardiometabolic Disorders
    (01-03-2022)
    Allu, Prasanna K.R.
    ;
    Kiranmayi, Malapaka
    ;
    Mukherjee, Sromona D.
    ;
    Chirasani, Venkat R.
    ;
    Garg, Richa
    ;
    Vishnuprabu, Durairajpandian
    ;
    Ravi, Sudesh
    ;
    Subramanian, Lakshmi
    ;
    Sahu, Bhavani S.
    ;
    Iyer, Dhanya R.
    ;
    Maghajothi, Sakthisree
    ;
    Sharma, Saurabh
    ;
    Ravi, Marimuthu S.
    ;
    Khullar, Madhu
    ;
    Munirajan, Arasambattu K.
    ;
    Gayen, Jiaur R.
    ;
    ;
    Mullasari, Ajit S.
    ;
    Mohan, Viswanathan
    ;
    Radha, Venkatesan
    ;
    Naga Prasad, Sathyamangala V.
    ;
    Pancreastatin (PST), a chromogranin A–derived potent physiological dysglycemic peptide, regulates glucose/insu-lin homeostasis. We have identified a nonsynonymous functional PST variant (p.Gly297Ser; rs9658664) that occurs in a large section of human populations. Association analysis of this single nucleotide polymorphism with cardiovas-cular/metabolic disease states in Indian populations (n 5 ~4,300 subjects) displays elevated plasma glucose, glyco-sylated hemoglobin, diastolic blood pressure, and cate-cholamines in Gly/Ser subjects as compared with wild-type individuals (Gly/Gly). Consistently, the 297Ser allele confers an increased risk (~1.3–1.6-fold) for type 2 diabe-tes/hypertension/coronary artery disease/metabolic syn-drome. In corroboration, the variant peptide (PST-297S) displays gain-of-potency in several cellular events relevant for cardiometabolic disorders (e.g., increased expression of gluconeogenic genes, increased catecholamine secre-tion, and greater inhibition of insulin-stimulated glucose uptake) than the wild-type peptide. Computational docking analysis and molecular dynamics simulations show higher affinity binding of PST-297S peptide with glucose-regu-lated protein 78 (GRP78) and insulin receptor than the wild-type peptide, providing a mechanistic basis for the enhanced activity of the variant peptide. In vitro binding assays validate these in silico predictions of PST peptides binding to GRP78 and insulin receptor. In conclusion, the PST 297Ser allele influences cardiovascular/metabolic phenotypes and emerges as a novel risk factor for type 2 diabetes/hypertension/coronary artery disease in human populations.
  • Placeholder Image
    Publication
    Structural plasticity of cholesteryl ester transfer protein assists the lipid transfer activity
    (09-09-2016)
    Chirasani, Venkat R.
    ;
    Revanasiddappa, Prasanna D.
    ;
    Cholesteryl ester transfer protein (CETP) mediates the transfer of cholesteryl esters (CEs) and triglycerides between different lipoproteins. Recent studies have shown that blocking the function of CETP can increase the level of HDL cholesterol in blood plasma and suppress the risk of cardiovascular disease. Hence, understanding the structure, dynamics, and mechanism by which CETP transfers the neutral lipids has received tremendous attention in last decade. Although the recent crystal structure has provided direct evidence of the existence of strongly bound CEs in the CETP core, very little is known about the mechanism of CE/triglyceride transfer by CETP. In this study, we explore the large scale dynamics of CETP by means of multimicrosecond molecular dynamics simulations and normal mode analysis, which provided a wealth of detailed information about the lipid transfer mechanism of CETP. Results show that the bound CEs intraconvert between bent and linear conformations in the CETP core tunnel as a consequence of the high degree of conformational flexibility of the protein. During the conformational switching, there occurred a significant reduction in hydrophobic contacts between the CEs and CETP, and a continuous tunnel traversing across the CETP long axis appeared spontaneously. Thus, our results support the recently proposed "tunnel mechanism" of CETP from cryo-EM studies for the transfer of neutral lipids between different lipoproteins. The detailed understanding obtained here could help in devising methods to prevent CETP function as a cardiovascular disease therapeutic.
  • Placeholder Image
    Publication
    Modulation of the mitochondrial voltage dependent anion channel (VDAC) by curcumin
    (01-01-2015)
    Tewari, Debanjan
    ;
    Ahmed, Tofayel
    ;
    Chirasani, Venkat R.
    ;
    Singh, Pradeep K.
    ;
    Maji, Samir K.
    ;
    ;
    Voltage dependent anion channel (VDAC) of mitochondria plays a crucial role in apoptosis. Human VDAC-1, reconstituted in planar lipid bilayer showed reduced conductance when treated with curcumin. Curcumin interacts with residues in the α helical N-terminus of VDAC and in the channel wall, as revealed by molecular docking, followed by mutational analysis. N-terminus mimicking peptide showed conformational changes in circular dichroism, upon curcumin treatment. We propose that the interaction of curcumin with amino acids in N-terminus and in channel wall fixes the α helix in closed conformation. This restricts its movement which is required for the opening of the channel.
  • Placeholder Image
    Publication
    Identifying crucial E-protein residues responsible for unusual stability of Zika virus envelope
    (21-09-2021)
    Pindi, Chinmai
    ;
    Chirasani, Venkat R.
    ;
    An outbreak of Zika virus (ZIKV) infections in 2015–16 that caused microcephaly and other congenital abnormalities in newborns prompted intense research across the globe. These studies have suggested that ZIKV can survive high temperatures and harsh physiological conditions, unlike the other flaviviruses such as dengue virus (DENV). In contrast, recent cryo-electron microscopy studies have shown very similar architecture of the ZIKV and DENV envelopes that constitute the primary level of viral protection. Encouraged by these findings, here we attempt to identify the crucial protein residues that make the ZIKV envelope so robust by employing coarse-grained and all-atomic molecular dynamics simulations and computational mutagenesis studies. In accordance with more recent cryo-electron microscopy findings, our simulation results exhibited stable ZIKV envelope protein shell both at 29oC and 40°C, whereas the DENV2 shell loosened up significantly at 40°C. Subsequently, we simulated a series of ZIKV variants to identify the specific domain and residues involved in maintaining the structural integrity of the viral protein shell at high temperatures. Our results suggest that the DIII domain—more specifically, the CD- and FG-loop residues of the ZIKV protein shell—play a crucial role in making the virus envelope thermostable by inducing strong raft-raft interactions. These findings can accelerate the rational design of ZIKV therapeutics.
  • Placeholder Image
    Publication
    Naturally occurring variants of the dysglycemic peptide pancreastatin: Differential potencies for multiple cellular functions and structure-function correlation
    (14-02-2014)
    Allu, Prasanna K.R.
    ;
    Chirasani, Venkat R.
    ;
    Ghosh, Dhiman
    ;
    Mani, Anitha
    ;
    ;
    Maji, Samir K.
    ;
    ;
    Mullasari, Ajit S.
    ;
    Background: Pancreastatin is a potent physiological regulator of plasma glucose/insulin. Results: We discovered two human variants of pancreastatin that are profoundly more potent than the wild-type peptide. Conclusion: Higher potencies of the variants correlate well with their enhanced propensity to adopt longer helical structures than the wild-type peptide. Significance: These findings provide new insights into the mechanism of human metabolic diseases. © 2014 by The American Society for Biochemistry and Molecular Biology, Inc..
  • Placeholder Image
    Publication
    Regulation of intestinal SGLT1 by catestatin in hyperleptinemic type 2 diabetic mice
    (01-01-2016)
    Dominguez Rieg, Jessica A.
    ;
    Chirasani, Venkat R.
    ;
    Koepsell, Hermann
    ;
    ;
    Mahata, Sushil K.
    ;
    Rieg, Timo
    The small intestine is the major site for nutrient absorption that is critical in maintenance of euglycemia. Leptin, a key hormone involved in energy homeostasis, directly affects nutrient transport across the intestinal epithelium. Catestatin (CST), a 21-amino acid peptide derived from proprotein chromogranin A, has been shown to modulate leptin signaling. Therefore, we reasoned that leptin and CST could modulate intestinal Na + -glucose transporter 1 (SGLT1) expression in the context of obesity and diabetes. We found that hyperleptinemic db/db mice exhibit increased mucosal mass, associated with an enhanced proliferative response and decreased apoptosis in intestinal crypts, a finding absent in leptin-deficient ob/ob mice. Intestinal SGLT1 abundance was significantly decreased in hyperleptinemic but not leptin-deficient mice, indicating leptin regulation of SGLT1 expression. Phlorizin, a SGLT1/2 inhibitor, was without effect in an oral glucose tolerance test in db/db mice. The alterations in architecture and SGLT1 abundance were not accompanied by changes in the localization of intestinal alkaline phosphatase, indicating intact differentiation. Treatment of db/db mice with CST restored intestinal SGLT1 abundance and intestinal turnover, suggesting a cross-talk between leptin and CST, without affecting plasma leptin levels. Consistent with this hypothesis, we identified structural homology between CST and the AB-loop of leptin and protein-protein docking revealed binding of CST and leptin with the Ig-like binding site-III of the leptin receptor. In summary, downregulation of SGLT1 in an obese type 2 diabetic mouse model with hyperleptinemia is presumably mediated via the short form of the leptin receptor and reduces overt hyperglycemia.
  • Placeholder Image
    Publication
    Mechanism of Inhibition of Cholesteryl Ester Transfer Protein by Small Molecule Inhibitors
    (25-08-2016)
    Chirasani, Venkat R.
    ;
    Sankar, Revathi
    ;
    Cholesteryl ester transfer protein (CETP) facilitates the bidirectional exchange of cholesteryl esters and triglycerides between high-density lipoproteins and low- or very low-density lipoproteins. Recent studies have shown that the impairment of lipid exchange processes of CETP can be an effective strategy for the treatment of cardiovascular diseases (CVDs). Understanding the molecular mechanism of CETP inhibition has, therefore, attracted tremendous attention in recent past. In this study, we explored the detailed mechanism of CETP inhibition by a series of recently reported small molecule inhibitors that are currently under preclinical testing. Our results from molecular dynamics simulations and protein-ligand docking studies suggest that the hydrophobic interactions between the CETP core tunnel residues and inhibitor moieties play a pivotal role, and physical occlusion of the CETP tunnel by these small molecules is the primary mechanism of CETP inhibition. Interestingly, bound inhibitors were found to increase the plasticity of CETP, which was explained by principal component analysis that showed a larger space of sampling of CETP C-domain due to inhibitor binding. The atomic-level details presented here could help accelerate the structure-based drug-discovery processes targeting CETP for CVD therapeutics.
  • Placeholder Image
    Publication
    Catestatin Gly364Ser Variant Alters Systemic Blood Pressure and the Risk for Hypertension in Human Populations via Endothelial Nitric Oxide Pathway
    (01-08-2016)
    Kiranmayi, Malapaka
    ;
    Chirasani, Venkat R.
    ;
    Allu, Prasanna K.R.
    ;
    Subramanian, Lakshmi
    ;
    Martelli, Elizabeth E.
    ;
    Sahu, Bhavani S.
    ;
    Vishnuprabu, Durairajpandian
    ;
    Kumaragurubaran, Rathnakumar
    ;
    Sharma, Saurabh
    ;
    Bodhini, Dhanasekaran
    ;
    ;
    Munirajan, Arasambattu K.
    ;
    Khullar, Madhu
    ;
    Radha, Venkatesan
    ;
    Mohan, Viswanathan
    ;
    Mullasari, Ajit S.
    ;
    Prasad, Sathyamangla V.Naga
    ;
    ;
    Catestatin (CST), an endogenous antihypertensive/antiadrenergic peptide, is a novel regulator of cardiovascular physiology. Here, we report case-control studies in 2 geographically/ethnically distinct Indian populations (n≈4000) that showed association of the naturally-occurring human CST-Gly364Ser variant with increased risk for hypertension (age-adjusted odds ratios: 1.483; P=0.009 and 2.951; P=0.005). Consistently, 364Ser allele carriers displayed elevated systolic (up to ≈8 mm Hg; P=0.004) and diastolic (up to ≈6 mm Hg; P=0.001) blood pressure. The variant allele was also found to be in linkage disequilibrium with other functional single-nucleotide polymorphisms in the CHGA promoter and nearby coding region. Functional characterization of the Gly364Ser variant was performed using cellular/molecular biological experiments (viz peptide-receptor binding assays, nitric oxide [NO], phosphorylated extracellular regulated kinase, and phosphorylated endothelial NO synthase estimations) and computational approaches (molecular dynamics simulations for structural analysis of wild-type [CST-WT] and variant [CST-364Ser] peptides and docking of peptide/ligand with β-adrenergic receptors [ADRB1/2]). CST-WT and CST-364Ser peptides differed profoundly in their secondary structures and showed differential interactions with ADRB2; although CST-WT displaced the ligand bound to ADRB2, CST-364Ser failed to do the same. Furthermore, CST-WT significantly inhibited ADRB2-stimulated extracellular regulated kinase activation, suggesting an antagonistic role towards ADRB2 unlike CST-364Ser. Consequently, CST-WT was more potent in NO production in human umbilical vein endothelial cells as compared with CST-364Ser. This NO-producing ability of CST-WT was abrogated by ADRB2 antagonist ICI 118551. In conclusion, CST-364Ser allele enhanced the risk for hypertension in human populations, possibly via diminished endothelial NO production because of altered interactions of CST-364Ser peptide with ADRB2 as compared with CST-WT.
  • Placeholder Image
    Publication
    How cholesteryl ester transfer protein can also be a potential triglyceride transporter
    (01-12-2017)
    Chirasani, Venkat R.
    ;
    CETP transfers cholesteryl esters (CEs) and triglycerides (TGs) between different lipoproteins and came in limelight as a drug-target against CVD. In the search for detailed mechanism of lipid transfer through CETP, enormous effort is devoted employing crystallographic, cryo-EM, and Molecular Dynamics (MD) studies. However, these studies primarily focused on CE-bound CETP structure and CE transfer mechanism. With the reported correlation that CETP looses significant CE transfer activity upon inhibiting TG transfer, it is of tremendous importance to understand the structure and dynamics of TG-bound CETP. Our results from large-scale all-atom and coarse-grained MD simulations show that CETP can accommodate two TG molecules in parallel N-N orientation with TG oleate chains majorly attaining the tuning-fork conformation. In TG-bound form, CETP not only maintained its secondary structures but also exhibited similar bending-twisting motions as reported for CE-CETP crystal structure. Obtained structural information are further validated by correlating to available functional data of 2-8 fold slower transfer rate of TG through CETP, where we show that TGs make 20% additional contacts with CETP compared to CEs. Identified CETP residues facilitating TG binding also match very well with reported mutagenesis data. The study could accelerate the drug-designing processes to combat CETP functionality and CVD.