Which Enzymes Do Viruses Interact With?

This review discusses the structural studies of viral enzymes, which are essential for the replication process within a host cell. Viral genomes exhibit diverse diversity, ranging from single-stranded DNA to double-stranded RNA. Viruses can quickly adapt to the host’s immune response and drug treatment, and they can translocate proteins and genetic material from the cell into new virus particles.

Viral enzymes, including protease, reverse transcriptase, and integrase, play a crucial role in the viral life cycle. Viruses do not grow through cell division but use the machinery and metabolism of a host cell to produce new copies of themselves. After infecting a host cell, a virion uses the cell’s enzymes to catalyze simple chemical reactions.

For most families of DNA viruses, transcription and DNA replication take place in the cell nucleus using cellular RNA polymerase II and other cellular enzymes. Innate immunity, one of the integral branches of the immune system, serves as the first line of host defense against invading pathogens. Coronaviruses use an unusually large collection of RNA-synthesizing and RNA-processing enzymes to express and replicate a genome that is two to three times larger than normal.

Viral enzymes are listed in fact sheets for each virus genus or family, and many viruses do contain enzymes in their virions. Retroviruses contain the enzymes needed for replication and integration. Reverse transcriptase, a viral enzyme, converts the viral RNA into a complementary strand of DNA.

Viruses have evolved multiple strategies to hijack cellular metabolic enzymes, increasing the expression of metabolic enzymes or promoting them. In such cases, viruses must encode their own enzymes, with the viral proteins produced varying from virus to virus.

Do viruses lack enzymes?

Viruses do carry enzymes both inside their capsid and on their envelopes. For example, the paramyxoviruses have a protein/enzyme that causes membrane fusion on its surface. As previously stated, the orthomyxoviruses have a enzyme called neuraminidase on their surface that facilitates escape from the host cell.

Do capsids have enzymes?

Longer versions of the capsid protein are also included and required for infection, most likely because they contain a phospholipase A2 enzyme activity, as well as basic sequences that control the nuclear transport of the capsids and capsid proteins during infection and replication.

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What enzyme replicates viral RNA?

DNA viruses use DNA as their genetic material, which can be double-stranded (dsDNA) or single-stranded (ssDNA). They replicate their genomes using DNA-dependent DNA polymerases and transcribe mRNA using DNA-dependent RNA polymerases. RNA viruses have RNA genomes that can be either double-stranded (dsRNA) or single-stranded (ssRNA), and their genomes can be either plus (+) sense or minus (−) sense. Reverse-transcribing viruses replicate using reverse transcription, a process for making DNA from RNA templates.

There are four possible types of polymerases found in viruses: RNA-dependent RNA polymerases, RNA-dependent DNA polymerases, DNA-dependent RNA polymerases, and DNA-dependent DNA polymerases. RNA-dependent RNA polymerases and reverse transcriptases are unique to viruses since the host cell does not require RNA replication or reverse transcription.

The main function of a polymerase is to copy a template nucleic acid strand to produce a daughter strand. The primary catalytic activity of a polymerase is to transfer a nucleotidyl moiety of an incoming nucleoside triphosphate (NTP) that is complementary to the template strand to the 3′-hydroxyl end of a growing daughter strand of RNA or DNA. Two divalent metal ions, such as Mg 2+ or Mn 2+, are required for polymerase activity. The polymerase active site must have binding sites for a template strand, the DNA or RNA primer terminus (the initiation “i” site), and the incoming NTP (the “i + 1” site).

The catalytic reaction steps consist of binding of template–primer and NTP, incorporation of nucleoside monophosphate into the growing daughter strand, release of pyrophosphate, and translocation along the template. Upon binding, the correct NTP is incorporated into the daughter strand via Watson–Crick base-pairing with the template base. The polymerase active site provides conserved Asp residues that coordinate the two metal ions.

In summary, DNA viruses use DNA as their genetic material and replicate their genomes using various polymerases. The two-metal mechanism used by polymerases is crucial for the successful replication and transcription of DNA and RNA.

What enzyme does a retrovirus use?

A type of virus that uses RNA as its genetic material. After infecting a cell, a retrovirus uses an enzyme called reverse transcriptase to convert its RNA into DNA. The retrovirus then integrates its viral DNA into the DNA of the host cell, which allows the retrovirus to replicate. HIV, the virus that causes AIDS, is a retrovirus.

What type of enzyme is carried in the capsid of a group 5 virus?

Class V: -ssRNA. Minus-strand RNA viruses include many members notable for humans, such as influenza virus, rabies virus, and Ebola virus. Since the genome of minus-strand RNA viruses cannot be used directly as mRNA, the virus must carry an RNA-dependent RNA-polymerase within its capsid. Upon entrance into the host cell, the plus-strand RNAs generated by the polymerase are used as mRNA for protein production. When viral genomes are needed the plus-strand RNAs are used as templates to make minus-strand RNA.

Class VI: +ssRNA, retroviruses. Despite the fact that the retroviral genome is composed of +ssRNA, it is not used as mRNA. Instead, the virus uses its reverse transcriptase to synthesize a piece of ssDNA complementary to the viral genome. The reverse transcriptase also possesses ribonuclease activity, which is used to degrade the RNA strand of the RNA-DNA hybrid. Lastly, the reverse transcriptase is used as a DNA polymerase to make a complementary copy to the ssDNA, yielding a dsDNA molecule. This allows the virus to insert its genome, in a dsDNA form, into the host chromosome, forming a provirus. Unlike a prophage, a provirus can remain latent indefinitely or cause the expression of viral genes, leading to the production of new viruses. Excision of the provirus does not occur for gene expression.

Viroids. Viroids are small, circular ssRNA molecules that lack protein. These infectious molecules are associated with a number of plant diseases. Since ssRNA is highly susceptible to enzymatic degradation, the viroid RNA has extensive complementary base pairing, causing the viroid to take on a hairpin configuration that is resistant to enzymes. For replication viroids rely on a plant RNA polymerase with RNA replicase activity.

Do viruses have a metabolic enzyme?

Metabolic enzymes are crucial for cell survival and maintaining cellular homeostasis. They play a wide spectrum of metabolic pathways due to their distinct enzymatic activity, including carboxylases, dehydrogenases, lipoxygenases, oxidoreductases, kinases, lyases, and transferases. As obligate intracellular pathogens, viruses rely on host cell machinery to power the biosynthesis of essential components for progeny production, such as nucleic acids, proteins, and lipids. To maximize progeny virion production, viruses have evolved strategies to hijack cellular metabolic enzymes.

Viruses can increase the expression of metabolic enzymes or promote their activation, serving essential roles in their replication. Some viruses, particularly herpesviruses, encode their own metabolic enzymes, which often catalyze the rate-limiting steps of nucleotide biosynthesis, thereby unleashing host cell restrictions to promote viral replication. This adaptation highlights the virus’s intricate strategy that co-opts cellular resources to benefit viral infection, ultimately promoting its successful replication and dissemination within the host.

Cellular metabolism also plays a pivotal role within the immune system, providing precursors and meeting the unique energy requirements associated with various immunological processes. Innate immunity, one of the integral branches of the immune system, serves as the first line of host defense against invading pathogens. Numerous enzymes are intrinsically capable of modulating host immunity, either by catalyzing rate-limiting steps or regulating the synthesis or consumption of metabolites that directly participate in immune signaling events. Certain metabolic enzymes have evolved to demonstrate unique enzymatic activity in the immune response, which is distinct from their conventional enzymatic activities.

Are restriction enzymes produced by viruses?

Restriction enzyme, a protein produced by bacteria that cleaves DNA at specific sites along the molecule. In the bacterial cell, restriction enzymes cleave foreign DNA, thus eliminating infecting organisms. Restriction enzymes can be isolated from bacterial cells and used in the laboratory to manipulate fragments of DNA, such as those that contain genes; for this reason they are indispensible tools of recombinant DNA technology ( genetic engineering ).

A bacterium uses a restriction enzyme to defend against bacterial viruses called bacteriophages, or phages. When a phage infects a bacterium, it inserts its DNA into the bacterial cell so that it might be replicated. The restriction enzyme prevents replication of the phage DNA by cutting it into many pieces. Restriction enzymes were named for their ability to restrict, or limit, the number of strains of bacteriophage that can infect a bacterium.

Each restriction enzyme recognizes a short, specific sequence of nucleotide bases (the four basic chemical subunits of the linear double-stranded DNA molecule— adenine, cytosine, thymine, and guanine ). These regions are called recognition sequences, or recognition sites, and are randomly distributed throughout the DNA. Different bacterial species make restriction enzymes that recognize different nucleotide sequences.

Which enzyme is used by some viruses to form DNA?

Reverse Transcriptase. Reverse Transcriptase is an enzyme that converts RNA into DNA, commonly found in retroviruses like HIV.

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Do viruses use their own catabolic enzymes?

Viruses are unable to produce catabolic enzymes to generate energy on their own. They could only do so by expressing their genomes either in the nucleus (for DNA viruses) or cytoplasm (for RNA viruses) of the host cell.

Do viruses make proteins?

I. Introduction. Viruses are unable to replicate on their own, and they need the intracellular environment and energy supplies to replicate. Indeed, they use the host translation machinery to synthesize their proteins, and the cell provides structures and/or host factors to achieve the synthesis of viral genomes. They also use cellular proteins and/or structures for intracellular transport and posttranslational modifications. Due to the structural and functional roles of cell membranes, major steps of the life cycle of viruses also depend on cellular membranes. A classic viral life cycle can be divided into three stages: early events (attachment to host cells, penetration, and uncoating) viral biosynthetic events (replication of the viral genome, transcription, and translation), and virion assembly and release ( Fig. 1 ). Studying how viral proteins interact with host cell membranes is therefore important to understand how viruses enter host cells, replicate their genome, and produce progeny particles.

Viral life cycle in eukaryotic cells. Viruses are obligate intracellular parasites. They enter host cells, they use host cell machineries to replicate their genome and synthesize their proteins, and they produce progeny virions that are released in the extracellular environment.

Because they are obligate intracellular parasites, viruses need to cross the plasma membrane in order to initiate their replication. To enter the cell, a virus needs to bind a receptor and sometimes a coreceptor before delivering its genome into the cytosol by crossing either the plasma membrane or the membrane of an endocytic vesicle. For enveloped viruses, specialized envelope glycoproteins (fusion proteins) will trigger fusion of the viral membrane with the cell membrane. Recent structural data on some fusion proteins allow a better understanding of how these proteins interact with cell membranes to induce the fusion process.