title: Contributions of Charged Residues in Structurally Dynamic Capsid Surface Loops to Rous Sarcoma Virus Assembly.
abstract: Extensive studies of orthoretroviral capsids have shown that many regions of the CA protein play unique roles at different points in the virus life cycle. The N-terminal domain (NTD) flexible-loop (FL) region is one such example: exposed on the outer capsid surface, it has been implicated in Gag-mediated particle assembly, capsid maturation, and early replication events. We have now defined the contributions of charged residues in the FL region of the Rous sarcoma virus (RSV) CA to particle assembly. Effects of mutations on assembly were assessed in vivo and in vitro and analyzed in light of new RSV Gag lattice models. Virus replication was strongly dependent on the preservation of charge at a few critical positions in Gag-Gag interfaces. In particular, a cluster of charges at the beginning of FL contributes to an extensive electrostatic network that is important for robust Gag assembly and subsequent capsid maturation. Second-site suppressor analysis suggests that one of these charged residues, D87, has distal influence on interhexamer interactions involving helix α7. Overall, the tolerance of FL to most mutations is consistent with current models of Gag lattice structures. However, the results support the interpretation that virus evolution has achieved a charge distribution across the capsid surface that (i) permits the packing of NTD domains in the outer layer of the Gag shell, (ii) directs the maturational rearrangements of the NTDs that yield a functional core structure, and (iii) supports capsid function during the early stages of virus infection.
  
  
  
  The production of infectious retrovirus particles is a complex process, a choreography of protein and nucleic acid that occurs in two distinct stages: formation and release from the cell of an immature particle followed by an extracellular maturation phase during which the virion proteins and nucleic acids undergo major rearrangements that activate the infectious potential of the virion. This study examines the contributions of charged amino acids on the surface of the Rous sarcoma virus capsid protein in the assembly of appropriately formed immature particles and the maturational transitions that create a functional virion. The results provide important biological evidence in support of recent structural models of the RSV immature virions and further suggest that immature particle assembly and virion maturation are controlled by an extensive network of electrostatic interactions and long-range communication across the capsid surface.
authors.affiliation: Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
authors.forename: Katrina J
authors.initials: KJ
authors.lastname: Heyrana
authors.affiliation: Department of Physics and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
authors.forename: Boon Chong
authors.initials: BC
authors.lastname: Goh
authors.affiliation: Department of Physics and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA jperilla@illinois.edu rcraven@psu.edu.
authors.forename: Juan R
authors.initials: JR
authors.lastname: Perilla
authors.affiliation: Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
authors.forename: Tam-Linh N
authors.initials: TN
authors.lastname: Nguyen
authors.affiliation: Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: England
authors.affiliation: Department of Biochemistry and Molecular Biology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
authors.forename: Maria C
authors.initials: MC
authors.lastname: Bewley
authors.affiliation: Department of Physics and Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
authors.forename: Klaus
authors.initials: K
authors.lastname: Schulten
authors.affiliation: Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA jperilla@illinois.edu rcraven@psu.edu.
authors.forename: Rebecca C
authors.initials: RC
authors.lastname: Craven
mesh_terms: D000595:Amino Acid Sequence; D002213:Capsid / Q000378:metabolism; D036022:Capsid Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020285:Cryoelectron Microscopy; D015683:Gene Products, gag / Q000737:chemistry* / Q000235:genetics; D008854:Microscopy, Electron; D008958:Models, Molecular; D009154:Mutation; D052736:Rous sarcoma virus / Q000737:chemistry* / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D055672:Static Electricity; D014771:Virion / Q000378:metabolism / Q000648:ultrastructure; D019065:Virus Assembly
chemical_list: D036022:Capsid Proteins; D015683:Gene Products, gag