Biology subjects

Vashisth, H.

Publications and source records attributed to Vashisth, H..

3 recordsLinked to original sources

bioRxiv2024

Viral Insulin/IGF-like Peptides Selectively Activate Host Insulin/IGF Signaling pathways during Grouper Iridovirus Infection

Until our recent discovery of viral insulin/IGF-1-like peptides (VILPs), examples of viral mimicry were mostly limited to immunomodulatory proteins and growth factors. We previously showed that six viruses in the Iridoviridae family encode genes mimicking insulin and IGF-1. While VILP-carrying viruses are isolated from fish, the role of VILPs in host-pathogen interactions remain elusive. In this study, we used the Grouper Iridovirus (GIV), one of the VILP-carrying viruses, to examine the impact of the GIV-VILPs on the host IGF-1R/IR system during infection. Our structural analysis revealed that GIV-VILP is 35% identical to both zebrafish insulin and 35 IGF-1. We also showed that GIV-VILPs are early viral transcripts and resulting peptides are secreted during viral infection. Both single-chain (sc, resembling IGF-1) and double chain (dc, resembling insulin) forms of chemically synthesized GIV-VILPs can stimulate insulin receptor (IR) and IGF-1 receptor (IGF1R) phosphorylation. They could also stimulatepost-receptor signaling in both grouper kidney (GK) and zebrafish AB.9 cells as potently as insulin. Notably, supernatants obtained from GIV-infected cells could stimulate insulin/IGF system in a dose dependent manner. Interestingly, GIV-VILP was able to selectively activate the Akt/PI3K pathway while had no or minimal effect on Erk/MAPK pathway. Using either IR, IGF1R or dual inhibitors, we illustrated that inhibition of IR signaling suppressed GIV viral replication while inhibition of IGF1R enhanced viral replication. Consistent with selective signaling action of PI3K/Akt pathway, inhibition of the Akt reduced GIV viral replication however Erk pathway inhibition did not affect it. In summary, GIV-VILP is produced during GIV infection and manipulates host insulin/IGF signaling in a selective manner. Our findings reveal a previously unknown viral strategy in which viruses mimic a host hormone to exploit the hosts endocrine system. This discovery unveils a novel viral pathogenesis mechanism, broadens our understanding of viral mimicry, and opens a new avenue to better understand viral strategies to manipulate the host.

microbiology↗

bioRxiv2024

Spontaneous Dimerization and Distinct Packing Modes of Transmembrane Domains in Receptor Tyrosine Kinases

The insulin receptor (IR) and the insulin-like growth factor-1 receptor (IGF1R) are homodimeric transmembrane glycoproteins that transduce signals across the membrane on binding of extracellular peptide ligands. The structures of IR/IGF1R fragments in apo and liganded states have revealed that the extracellular subunits of these receptors adopt {Lambda}-shaped configurations to which are connected the intracellular tyrosine kinase (TK) domains. The binding of peptide ligands induces structural transitions in the extracellular subunits leading to potential dimerization of transmembrane domains (TMDs) and autophosphorylation in TKs. However, the activation mechanisms of IR/IGF1R, especially the role of TMDs in coordinating signal-inducing structural transitions, remain poorly understood, in part due to the lack of structures of full-length receptors in apo or liganded states. While atomistic simulations of IR/IGF1R TMDs showed that these domains can dimerize in single component membranes, spontaneous unbiased dimerization in a plasma membrane having physiologically representative lipid composition has not been observed. We address this limitation by employing coarsegrained (CG) molecular dynamics simulations to probe the dimerization propensity of IR/IGF1R TMDs. We observed that TMDs in both receptors spontaneously dimerized independent of their initial orientations in their dissociated states, signifying their natural propensity for dimerization. In the dimeric state, IR TMDs predominantly adopted X-shaped configurations with asymmetric helical packing and significant tilt relative to the membrane normal, while IGF1R TMDs adopted symmetric V-shaped or parallel configurations with either no tilt or a small tilt relative to the membrane normal. Our results suggest that IR/IGF1R TMDs spontaneously dimerize and adopt distinct dimerized configurations. TOC Graphic O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=111 SRC="FIGDIR/small/593448v3_ufig1.gif" ALT="Figure 1"> View larger version (15K): org.highwire.dtl.DTLVardef@107bfdforg.highwire.dtl.DTLVardef@1c5ca00org.highwire.dtl.DTLVardef@50d859org.highwire.dtl.DTLVardef@1abc266_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2024

Structural Models for a Series of Allosteric Inhibitors of IGF1R Kinase

The allosteric inhibition of Insulin-like Growth Factor Receptor 1 Kinase (IGF1RK) is a potential strategy to overcome selectivity barriers in targeting receptor tyrosine kinases. We constructed structural models of a series of 12 indole-butyl-amine derivatives which have been reported as allosteric inhibitors of IGF1RK. We further studied dynamics and interactions of each inhibitor in the allosteric pocket via all-atom explicit-solvent molecular dynamics (MD) simulations. We discovered that a bulky carbonyl substitution at the R1 indole ring is structurally unfavorable for inhibitor binding in the IGF1RK allosteric pocket. Moreover, we found that the most potent derivative (termed C11) acquires a distinct conformation, forming an allosteric pocket channel with better shape complementarity and interactions with the receptor. In addition to a hydrogen bonding interaction with V1063, the cyano derivative C11 forms a stable hydrogen bond with M1156, which is responsible for its unique binding conformation in the allosteric pocket. Our findings show that the position of chemical substituents at the R1 indole ring with different pharmacophore features influences molecular interactions and binding conformations of the indole-butyl-amine derivatives, hence dramatically affecting their potencies. Our results provide a structural framework for the design of allosteric inhibitors with improved affinities and specificities against IGF1RK.

biophysics↗