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The Viruses
Published in Julius P. Kreier, Infection, Resistance, and Immunity, 2022
The structural proteins surrounding viral genomes are arranged into one of two symmetrical forms called capsids that are either helical or icosahedral in shape. The simplest viruses consist of a rodlike helix or coil of RNA closely associated with structural proteins. There are no known animal viruses lacking an outer envelope and thus naked helical morphology; however, an example of one found in plants is the tobacco mosaic virus. The simplest animal viruses are naked icosahedral viruses such as the parvoviruses. They consist of a DNA or RNA strand within a protein shell called a capsid (Figure 16.1 A). The capsid consists of a structure created by the regular arrangement of structural subunits called “capsomeres.” Each capsomer is composed of a set of viral structural proteins. The other major forms of viruses are the enveloped icosahedral viruses such as the herpesviruses or the enveloped helical viruses such as the rhabdoviruses (Figure 16.1 B and 16.1C). Viral nucleic acid strands with bound proteins generally have helical morphology while viral genomes within a capsid structure also referred to as a nucleocapsid are characteristically icosahedral in morphology.
Virus-Based Nanocarriers for Targeted Drug Delivery
Published in Devarajan Thangadurai, Saher Islam, Charles Oluwaseun Adetunji, Viral and Antiviral Nanomaterials, 2022
Semra Akgönüllü, Monireh Bakhshpour, Yeşeren Saylan, Adil Denizli
The viral capsids, as outer protein walls, package the genome of the virus that is used in the delivery of drug molecules. The capsid proteins have governed by the packaging of the viral genome (RNA or DNA). Sequence and structural properties of the capsid protein and the viral RNA(s) play a magnificent role in genome packaging such as disassembly or self-assembly processes (Speir and Johnson 2012). The mechanism of virus packaging plays a significant role in drug delivery enforcement through reengineering capsids or blocking viral propagation. The capsid proteins can be reassembled into null viruses-like nanoparticles. So, this specific coat protein content can be able to utilise in drug delivery systems. These viruses-like nanoparticles have a rod-shaped and/or spherical shape.
SARS-CoV-2 Morphology, Genomic Organisation and Lifecycle
Published in Srijan Goswami, Chiranjeeb Dey, COVID-19 and SARS-CoV-2, 2022
Srijan Goswami, Ushmita Gupta Bakshi
The capsid, located just below the viral envelope, is a thin shell made up of proteins and encloses the genetic material of the virus. Nucleocapsid proteins are located below the capsid, associated with the viral genetic material, and thus create a protective covering around it. The nucleocapsid plays three critical roles in the virus lifecycle (UniProtKB – P59595, n.d.). First, it protects viral particles by inhibiting the host's defence mechanisms, second, it assists viral RNA in replicating itself, and third, it aids in the generation of new viral particles (UniProtKB – P59595, n.d.).
Mechanisms of cellular and humoral immunity through the lens of VLP-based vaccines
Published in Expert Review of Vaccines, 2022
Hunter McFall-Boegeman, Xuefei Huang
Virus-like particles (VLPs) are protein-based nanoparticles made up of repeating copies of a coat protein(s). These structures usually include the surface proteins and another macromolecule (RNA, DNA, or protein) encapsulated to aid in the assembly of a capsid[17,18]. Because of their viral origin, VLPs almost always contain a helper T cell epitope that can boost the immune response and bias it towards a long-lasting immunological memory[19]. Initial forays into the use of VLPs in vaccination strategies utilized human viral capsids such as Hepatitis B surface antigen (HBsAg) or Human Papilloma Virus (HPV) L1 Major Capsid Protein[20,21]. Commercial vaccines against HPV and hepatitis B have been approved using recombinant VLPs. These vaccines have been safe and widely effective[22–24]. Yet, there is much to learn based on clinical observations, such as the effect of age of vaccination on levels of antibodies elicited[25].
Role of structural disorder in the multi-functionality of flavivirus proteins
Published in Expert Review of Proteomics, 2022
Shivani Krishna Kapuganti, Aparna Bhardwaj, Prateek Kumar, Taniya Bhardwaj, Namyashree Nayak, Vladimir N. Uversky, Rajanish Giri
The capsid protein interacts with lipids and helps in encapsidation of the viral genome. Its function may be similar to cellular histones in that it may have a role in charge neutralization and compaction of RNA [69]. The PrM associates with envelope protein and protects the fusion peptide. The cleavage of PrM give rise to mature membrane protein which is required to form an infectious virion [70]. The surface envelope glycoprotein mediates entry into host cells such as epidermal keratinocytes, fibroblasts, immature dendritic cells, stem cells derived human neural progenitors etc. It has three domains – EDI, EDII, and EDIII – which initiate fusion with a highly hydrophobic fusion loop and contains putative receptor-binding sites [71,72]. The fusion peptide region is present at the end of EDII. EDIII serves as a receptor attachment domain and also acts as an antigenic determinant site.
Differential expression of miRNAs in a human developing neuronal cell line chronically infected with Zika virus
Published in Libyan Journal of Medicine, 2021
Omar Bagasra, Narges Sadat Shamabadi, Pratima Pandey, Abdelrahman Desoky, Ewen McLean
Capsid protein is a ~ 12-kDa protein comprising the first ~105 residues of the ZIKV polyprotein. Capsid is the primary structural protein that interacts with the viral genome within virus particles and is essential for efficient packaging. Capsid dimers can bind a wide range of nucleic acid templates including the host RNAs, interfering in RNA splicing and RNA transcription. Capsid also enter the nucleolus and interacts with miRNAs and, therefore, may quell the molecular immune response against ZIKV [20,22]. Capsid protein expresses hydrophobic and hydrophilic regions that appear to play important roles in the pathogenesis of the virus. Capsid also causes significant dysregulation of host ribosomal biogenesis [20,22–25]. The hydrophobic regions of capsid proteins interact with the membrane of the endoplasmic reticulum (ER) whereas the hydrophilic region interacts with viral RNA. Binding of RNA to capsid starts particle formation by initiating aggregation of capsid. The aggregation of membrane-associated capsid into the nucleocapsid structure induces budding into the ER and the formation of immature virus particles. Capsid protein binds ssRNA, dsRNA and DNA in a sequence-independent manner via electrostatic interactions with the negatively charged phosphate backbone [20]. The packaging inside ER membrane compartments precludes capsid from packaging host RNAs.