Transcriptional Control and mRNA Capping by the GDP Polyribonucleotidyltransferase Domain of the Rabies Virus Large Protein

Abstract

Rabies virus (RABV) is a causative agent of a fatal neurological disease in humans and animals. The large (L) protein of RABV is a multifunctional RNA-dependent RNA polymerase, which is one of the most attractive targets for developing antiviral agents. A remarkable homology of the RABV L protein to a counterpart in vesicular stomatitis virus, a well-characterized rhabdovirus, suggests that it catalyzes mRNA processing reactions, such as 5′-capping, cap methylation, and 3′-polyadenylation, in addition to RNA synthesis. Recent breakthroughs in developing in vitro RNA synthesis and capping systems with a recombinant form of the RABV L protein have led to significant progress in our understanding of the molecular mechanisms of RABV RNA biogenesis. This review summarizes functions of RABV replication proteins in transcription and replication, and highlights new insights into roles of an unconventional mRNA capping enzyme, namely GDP polyribonucleotidyltransferase, domain of the RABV L protein in mRNA capping and transcription initiation.

Structure of a rabies virus polymerase complex from electron cryo-microscopy

“…The nascent RNA transcript with a 5′ triphosphate is first covalently linked to a catalytic histidine residue (H1241) in a reaction that leads to a monophosphate RNA-L intermediate. This linkage is subsequently thought to be attacked by a GTP molecule, resulting in addition of GDP to the monophosphate-RNA to form a GTP-capped pre-mRNA (23). Several residues in both RABV and VSV CAP that affect cap addition have been identified, including the GxxT and HR motifs broadly conserved throughout Mononegavirales (1,24).…”

RNA Synthesis and Capping by Non-segmented Negative Strand RNA Viral Polymerases: Lessons From a Prototypic Virus

“…Importantly, a recombinant form of the VSV L protein as well as native VSV L–P and RNP complexes was shown to catalyze the unique RNA capping reaction (Ogino and Banerjee, 2007). In striking contrast to the mononucleotide (GMP or m 7 GMP) transfer mechanisms employed by eukaryotes and other viruses (Figure 7A–C), rhabdoviruses, such as VSV (Ogino and Banerjee, 2007, 2008; Ogino et al, 2010), Chandipura virus (CHPV, Vesiculovirus ) (Ogino and Banerjee, 2010), and RABV ( Lyssavirus ) (Ogino et al, 2016; Ogino and Green, 2019), use a polynucleotide transfer mechanism to generate the cap core structure (Figure 7D). In the first step of the cap formation, the L protein-associated guanosine 5′-triphosphatase (GTPase) activity removes the γ-phosphate of GTP to generate GDP (Ogino and Banerjee, 2007, 2008).…”

“…In sharp contrast to eukaryotic capping enzyme (Venkatesan and Moss, 1980), the VSV L protein is able to cap pppRNAs, but not ppRNAs, with GDP (Ogino and Banerjee, 2007). Similarly, the RABV L protein specifically caps pppRNAs, but not ppRNAs, with the lyssaviral mRNA-start sequence 5′-AACA(C/U), in which the 5′-terminal AAC sequence is critical for the substrate activity (Ogino et al, 2016; Ogino and Green, 2019). Unlike the VSV L protein, the RABV L protein does not accept pppAGC-RNA as a pRNA donor substrate (Ogino et al, 2016).…”

Components and Architecture of the Rhabdovirus Ribonucleoprotein Complex

“…The L-protein is the enzymatically active component of the transcriptase and replicase complex (reviewed in [74]), with a molecular weight of 242 kD. The enzymatic activities of the L-protein include an RNA-dependent RNA-polymerase (RdRp, aa 35-865, positions are given for VSV) [6], a GDP polyribonucleotidyl transferase (aa 866-1334) [75], a methyltransferase (aa 1598-1892) [76][77][78][79] and it also acts as a polyadenylase [80].…”