Hydrophobic segment of dengue virus C protein. Interaction with model membranes

Lipid Droplets: Formation, Degradation, and Their Role in Cellular Responses to Flavivirus Infections

Lipid droplets (LDs) are cellular organelles derived from the endoplasmic reticulum (ER), serving as lipid storage sites crucial for maintaining cellular lipid homeostasis. Recent attention has been drawn to their roles in viral replication and their interactions with viruses. However, the precise biological functions of LDs in viral replication and pathogenesis remain incompletely understood. To elucidate the interaction between LDs and viruses, it is imperative to comprehend the biogenesis of LDs and their dynamic interactions with other organelles. In this review, we explore the intricate pathways involved in LD biogenies within the cytoplasm, encompassing the uptake of fatty acid from nutrients facilitated by CD36-mediated membranous protein (FABP/FATP)-FA complexes, and FA synthesis via glycolysis in the cytoplasm and the TCL cycle in mitochondria. While LD biogenesis primarily occurs in the ER, matured LDs are intricately linked to multiple organelles. Viral infections can lead to diverse consequences in terms of LD status within cells post-infection, potentially involving the breakdown of LDs through the activation of lipophagy. However, the exact mechanisms underlying LD destruction or accumulation by viruses remain elusive. The significance of LDs in viral replication renders them effective targets for developing broad-spectrum antivirals. Moreover, considering that reducing neutral lipids in LDs is a strategy for anti-obesity treatment, LD depletion may not pose harm to cells. This presents LDs as promising antiviral targets for developing therapeutics that are minimally or non-toxic to the host.

Simultaneous membrane and RNA binding by tick-borne encephalitis virus capsid protein

Tick-borne encephalitis virus is an enveloped, pathogenic, RNA virus in the family Flaviviridae, genus Flavivirus. Viral particles are formed when the nucleocapsid, consisting of an RNA genome and multiple copies of the capsid protein, buds through the endoplasmic reticulum membrane and acquires the viral envelope and the associated proteins. The coordination of the nucleocapsid components to the sites of assembly and budding are poorly understood. Here, we investigate the interactions of the wild-type and truncated capsid proteins with membranes with biophysical methods and model membrane systems. We show that capsid protein initially binds membranes via electrostatic interactions with negatively-charged lipids, which is followed by membrane insertion. Additionally, we show that membrane-bound capsid protein can recruit viral genomic RNA. We confirm the biological relevance of the biophysical findings by using mass spectrometry to show that purified virions contain negatively-charged lipids. Our results suggest that nucleocapsid assembly is coordinated by negatively-charged membrane patches on the endoplasmic reticulum and that the capsid protein mediates direct contacts between the nucleocapsid and the membrane.

Seeking heterocyclic scaffolds as antivirals against dengue virus

Dengue is one of the most typical viral infection categorized in the Neglected Tropical Diseases (NTDs). It is transmitted via the female Aedes aegypti mosquito to humans and majorly puts risk to the lives of more than half of the world. Recent advancements in medicinal chemistry have led to the design and development of numerous potential heterocyclic scaffolds as antiviral drug candidates for the inhibition of the dengue virus (DENV). Thus, in this review, we have discussed the significance of inhibitory and antiviral activities of nitrogen, oxygen, and mixed (nitrogen-sulfur and nitrogen-oxygen) heterocyclic scaffolds that are published in the last seven years (2016–2022). Furthermore, we have also discussed the probable mechanisms of action and the diverse structure-activity relationships (SARs) of the heterocyclic scaffolds. In addition, this review has elaborately outlined the mechanism of viral infection and the life cycle of DENV in the host cells. The wide set of heterocycles and their SARs will aid in the development of pharmaceuticals that will allow the researchers to synthesize the promising anti-dengue drug candidate in the future.

Dengue virus entry/fusion inhibition by small bioactive molecules; A critical review

Many flaviviruses are remarkable human pathogens that can be transmitted by mosquitoes and ticks. Despite the availability of vaccines for viral infections such as yellow fever, Japanese encephalitis, and tick-borne encephalitis, flavivirus-like dengue is still a significant life-threatening illness worldwide. To date, there is no antiviral treatment for dengue therapy. Industry and the research community have been taking ongoing steps to improve anti-flavivirus treatment to meet this clinical need. The successful activity has been involved in the inhibition of the virus entry fusion process in the last two decades. In this study, the latest understanding of the use of small molecules used as fusion inhibitors has been comprehensively presented. We summarized the structure, the process of fusion of dengue virus E protein (DENV E), and the amino acids involved in the fusion process. Special attention has been given to small molecules that allow conformational changes to DENV E protein viz. blocking the pocket of βOG, which is important for fusion.

Structure and function of capsid protein in flavivirus infection and its applications in the development of vaccines and therapeutics

Flaviviruses are enveloped single positive-stranded RNA viruses. The capsid (C), a structural protein of flavivirus, is dimeric and alpha-helical, with several special structural and functional features. The functions of the C protein go far beyond a structural role in virions. It is not only responsible for encapsidation to protect the viral RNA but also able to interact with various host proteins to promote virus proliferation. Therefore, the C protein plays an important role in infected host cells and the viral life cycle. Flaviviruses have been shown to affect the health of humans and animals. Thus, there is an urgent need to effectively control flavivirus infections. The structure of the flavivirus virion has been determined, but there is relatively little information about the function of the C protein. Hence, a greater understanding of the role of the C protein in viral infections will help to discover novel antiviral strategies and provide a promising starting point for the further development of flavivirus vaccines or therapeutics.

Amplificación de la infección dependiente de anticuerpos en la inmunopatogénesis del dengue grave, implicaciones para el desarrollo y uso de las vacunas

Actualmente, la infección por el virus de dengue (DENV) es uno de los problemas más importantes de salud pública en países tropicales y endémicos como Colombia, pues en tanto puede ser producida por cuatro diferentes serotipos virales, durante las infecciones secundarias se presentan frecuentemente cuadros más severos que incluso pueden llevar a desenlaces fatales. El centro de la fisiopatología del dengue grave es el daño producido al endotelio, que se traduce en un aumento en la permeabilidad vascular que se evidencia como fuga plasmática, descontrol en la coagulación y daño de órganos. Aunque hay varias teorías que explican la enfermedad severa, el fenómeno denominado amplificación de la infección dependiente de anticuerpos (antibody dependent enhancement, ADE) es el más conocido. En este, se postula que el virus causante de una infección secundaria es reconocido, pero no neutralizado, por anticuerpos generados en la infección previa e internalizado en las células susceptibles usando receptores Fc-gamma, lo cual aumenta la replicación viral e induce modificaciones en la respuesta inmune celular que contribuyen al desarrollo de dengue grave. En este escrito, se realiza una revisión de los hallazgos sobre los mecanismos involucrados en el fenómeno de ADE y cómo pueden contribuir a la progresión hacia dengue grave, describiendo los conceptos de ADE extrínseco e intrínseco, además de como este fenómeno debe ser tenido en cuenta para el diseño, desarrollo e implementación de una vacuna para dengue, en tanto es capaz de afectar su eficacia y seguridad.

Antiviral Activity of a Turbot (Scophthalmus maximus) NK-Lysin Peptide by Inhibition of Low-pH Virus-Induced Membrane Fusion

Global health is under attack by increasingly-frequent pandemics of viral origin. Antimicrobial peptides are a valuable tool to combat pathogenic microorganisms. Previous studies from our group have shown that the membrane-lytic region of turbot (Scophthalmus maximus) NK-lysine short peptide (Nkl_71–100) exerts an anti-protozoal activity, probably due to membrane rupture. In addition, NK-lysine protein is highly expressed in zebrafish in response to viral infections. In this work several biophysical methods, such as vesicle aggregation, leakage and fluorescence anisotropy, are employed to investigate the interaction of Nkl_71–100 with different glycerophospholipid vesicles. At acidic pH, Nkl_71–100 preferably interacts with phosphatidylserine (PS), disrupts PS membranes, and allows the content leakage from vesicles. Furthermore, Nkl_71–100 exerts strong antiviral activity against spring viremia of carp virus (SVCV) by inhibiting not only the binding of viral particles to host cells, but also the fusion of virus and cell membranes, which requires a low pH context. Such antiviral activity seems to be related to the important role that PS plays in these steps of the replication cycle of SVCV, a feature that is shared by other families of virus-comprising members with health and veterinary relevance. Consequently, Nkl_71–100 is shown as a promising broad-spectrum antiviral candidate.

Properties and Functions of the Dengue Virus Capsid Protein

Dengue virus affects hundreds of millions of people each year around the world, causing a tremendous social and economic impact on affected countries. The aim of this review is to summarize our current knowledge of the functions, structure, and interactions of the viral capsid protein. The primary role of capsid is to package the viral genome. There are two processes linked to this function: the recruitment of the viral RNA during assembly and the release of the genome during infection. Although particle assembly takes place on endoplasmic reticulum membranes, capsid localizes in nucleoli and lipid droplets. Why capsid accumulates in these locations during infection remains unknown. In this review, we describe available data and discuss new ideas on dengue virus capsid functions and interactions. We believe that a deeper understanding of how the capsid protein works during infection will create opportunities for novel antiviral strategies, which are urgently needed to control dengue virus infections.

Understanding Dengue Virus Capsid Protein Interaction with Key Biological Targets

Dengue virus (DENV) causes over 500,000 hospitalizations and 20,000 deaths worldwide every year. Dengue epidemics now reach temperate regions due to globalization of trade and travel and climate changes. Currently, there are no successful therapeutic or preventive approaches. We previously developed a peptide drug lead, pep14-23, that inhibits the biologically relevant interaction of DENV capsid (C) protein with lipid droplets (LDs). Surprisingly, pep14-23 also inhibits DENV C interaction with very low-density lipoproteins (VLDL). We thus investigated the similarity between the proposed DENV C molecular targets in LDs and VLDL, respectively, the proteins perilipin 3 (PLIN3) and apolipoprotein E (APOE). APOE N-terminal and PLIN3 C-terminal regions are remarkably similar, namely APOE α-helix 4 (APOEα4) and PLIN3 α-helix 5 (PLIN3α5) sequences, which are also highly superimposable structurally. Interestingly, APOE α-helical N-terminal sequence and structure superimposes with DENV C α-helices α1 and α2. Moreover, the DENV C hydrophobic cleft can accommodate the structurally analogous APOEα4 and PLIN3α5 helical regions. Mirroring DENV C-LDs interaction (previously shown experimentally to require PLIN3), we experimentally demonstrated that DENV C-VLDL interaction requires APOE. Thus, the results fit well with previous data and suggest future drug development strategies targeting the above mentioned α-helical structures.

gH625: a milestone in understanding the many roles of membranotropic peptides

Here, we review the current knowledge about viral derived membranotropic peptides, and we discuss how they may be used for many therapeutic applications. While they have been initially discovered in viral fusion proteins and have been involved in the mechanism of viral entry, it is now clear that their features and their mode of interaction with membrane bilayers can be exploited to design viral inhibitors as well as to favor delivery of cargos across the cell membrane and across the blood–brain barrier. The peptide gH625 has been extensively used for all these purposes and provides a significant contribution to the field. We describe the roles of this sequence in order to close the gap between the many functions that are now emerging for membranotropic peptides.

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Membranotropic peptides and their therapeutic applications

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Membrane fusion, viral inhibition, drug delivery

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gH625, a peptide derived from Herpes simplex virus type I: a case study

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gH625 in vitro and in vivo delivery across the blood–brain barrier