Du Pont V, Jiang Y, Plemper RK. Bipartite interface of the measles virus phosphoprotein X domain with the large polymerase protein regulates viral polymerase dynamics.
PLoS Pathog 2019;
15:e1007995. [PMID:
31381607 PMCID:
PMC6695210 DOI:
10.1371/journal.ppat.1007995]
[Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2019] [Revised: 08/15/2019] [Accepted: 07/22/2019] [Indexed: 11/18/2022] Open
Abstract
Measles virus (MeV) is a highly contagious, re-emerging, major human pathogen. Replication requires a viral RNA-dependent RNA polymerase (RdRP) consisting of the large (L) polymerase protein complexed with the homo-tetrameric phosphoprotein (P). In addition, P mediates interaction with the nucleoprotein (N)-encapsidated viral RNA genome. The nature of the P:L interface and RdRP negotiation of the ribonucleoprotein template are poorly understood. Based on biochemical interface mapping, swapping of the central P tetramerization domain (OD) for yeast GCN4, and functional assays, we demonstrate that the MeV P-to-L interface is bipartite, comprising a coiled-coil microdomain proximal to the OD and an unoccupied face of the triangular prism-shaped C-terminal P X-domain (P-XD), which is distinct from the known P-XD face that binds N-tail. Mixed null-mutant P tetramers regained L-binding competence in a ratio-dependent manner and fully reclaimed bioactivity in minireplicon assays and recombinant MeV, demonstrating that the individual L-binding interface elements are physically and mechanistically distinct. P-XD binding competence to L and N was likewise trans-complementable, which, combined with mathematical modeling, enabled the mechanistic characterization of P through two- and stoichiometrically-controlled three-way complementations. Only one each of the four XDs per P tetramer must be L or N binding-competent for bioactivity, but interaction of the same P-XD with L and N was mutually exclusive, and L binding superseded engaging N. Mixed P tetramers with a single, designated L binding-competent P-XD caused significant RdRP hyperactivity, outlining a model of iterative resolution and reformation of the P-XD:L interface regulating polymerase mobility.
MeV belongs to the order of non-segmented negative polarity RNA viruses, which includes devastating human pathogens. While all feature encapsidated RNA genomes and P-L type polymerase complexes, insight into the intermolecular interactions within the polymerase hetero-oligomer and between the polymerase complex and the RNA-encapsidating N protein is rudimentary. Our mapping of the MeV P-to-L interaction revealed a bipartite interface with physically and mechanistically distinct contact zones, which provided a unique experimental platform to dissect the stoichiometry and dynamics of P interactions with L and N through functional trans-complementation assays in minireplicon settings and, ensuring physiological significance, recombinant virions. The identification and functional characterization of a novel L-binding face on the P-XD triangular prism, distinct from the side contacting N-tail, places P-XD at the center of a regulatory mechanism that controls the dynamics of polymerase advancement along the encapsidated genome through iterative separation and restoration of P-XD interaction with L. These observations and the high structural homology of polymerase components within the Paramyxoviridae recommend the P-XD:L protein-protein interface as premier target for directed drug discovery against emerging and re-emerging paramyxoviruses.
Collapse