Biochemistry of the Respiratory Syncytial Virus L Protein Embedding RNA Polymerase and Capping Activities

Abstract

The human respiratory syncytial virus (RSV) is a negative-sense, single-stranded RNA virus. It is the major cause of severe acute lower respiratory tract infection in infants, the elderly population, and immunocompromised individuals. There is still no approved vaccine or antiviral treatment against RSV disease, but new monoclonal prophylactic antibodies are yet to be commercialized, and clinical trials are in progress. Hence, urgent efforts are needed to develop efficient therapeutic treatments. RSV RNA synthesis comprises viral transcription and replication that are catalyzed by the large protein (L) in coordination with the phosphoprotein polymerase cofactor (P), the nucleoprotein (N), and the M2-1 transcription factor. The replication/transcription is orchestrated by the L protein, which contains three conserved enzymatic domains: the RNA-dependent RNA polymerase (RdRp), the polyribonucleotidyl transferase (PRNTase or capping), and the methyltransferase (MTase) domain. These activities are essential for the RSV replicative cycle and are thus considered as attractive targets for the development of therapeutic agents. In this review, we summarize recent findings about RSV L domains structure that highlight how the enzymatic activities of RSV L domains are interconnected, discuss the most relevant and recent antivirals developments that target the replication/transcription complex, and conclude with a perspective on identified knowledge gaps that enable new research directions.

Viral RNA capping: Mechanisms and antiviral therapy

“…21 In the meanwhile, some viral capping enzyme most likely has multiple functions. 1 Some viral capping enzymes also have extra transcription-related functions such as controlling access to the virus replication factories, 22 nucleic acid unwinding, 23 RdRp, 24,25 transcription termination regulation, 26 transcription proofreading, 27 and poly(A) polymerase, 28 which promotes the efficiency of viral transcription.…”

Small Molecule Drugs Targeting Viral Polymerases

“…It encompasses hallmark subdomains-the palm (residues 692-705 and 774-878), fingers (residues 434-659 and 706-773), and thumb (residues 879-968)-each contributing to catalysis and RNA binding. The catalytic motif, Gly810-Asp811-Asn812q, along with Asp700, coordinates two requisite Mg 2+ ions required for phosphodiester bond formation [133]. Ranging from residues 969 to 1460, the polyribonucleotidyl transferase (PRNTase or capping) domain governs crucial capping processes by adding a protective chemical group (cap) to the newly synthesized viral RNA transcripts.…”

Development of a Melting-Curve-Based Multiplex Real-Time PCR Assay for the Simultaneous Detection of Viruses Causing Respiratory Infection

“…These genes have been studied as potential therapeutic targets for the developme of antiviral agents [4,[41][42][43][44], reinforcing their crucial role in viral life cycles. For SAR CoV-2, genes encoding RdRp (ORF1ab) and N (gene: N) proteins were selected for prim design in this study.…”

“…The N protein is the most abundant in virions and pla several essential roles in the SARS-CoV-2 life cycle, including transcription, the replicatio of the viral genome, the encapsidation of the viral genome into a ribonucleotide comple and assembly into viral particles [47]. These genes have been studied as potential therapeutic targets for the development of antiviral agents [4,[41][42][43][44], reinforcing their crucial role in viral life cycles. For SARS-CoV-2, genes encoding RdRp (ORF1ab) and N (gene: N) proteins were selected for primer design in this study.…”

“…The L protein of HRSV contains an RdRp domain (RNA transcription/replication), a polyribonucleotidyltransferase (cap addition) domain, and a methyltransferase (cap methylation) domain, all of which are indispensable for the viral replicative cycle. Notably, the C-terminal region of the L protein is the most variable domain among non-segmented negative-strand viruses [44].…”