title: The assembly pathway of an icosahedral single-stranded RNA virus depends on the strength of inter-subunit attractions.
abstract: The strength of attraction between capsid proteins (CPs) of cowpea chlorotic mottle virus (CCMV) is controlled by the solution pH. Additionally, the strength of attraction between CP and the single-stranded RNA viral genome is controlled by ionic strength. By exploiting these properties, we are able to control and monitor the in vitro co-assembly of CCMV CP and single-stranded RNA as a function of the strength of CP-CP and CP-RNA attractions. Using the techniques of velocity sedimentation and electron microscopy, we find that the successful assembly of nuclease-resistant virus-like particles (VLPs) depends delicately on the strength of CP-CP attraction relative to CP-RNA attraction. If the attractions are too weak, the capsid cannot form; if they are too strong, the assembly suffers from kinetic traps. Separating the process into two steps-by first turning on CP-RNA attraction and then turning on CP-CP attraction-allows for the assembly of well-formed VLPs under a wide range of attraction strengths. These observations establish a protocol for the efficient in vitro assembly of CCMV VLPs and suggest potential strategies that the virus may employ in vivo.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA.
authors.forename: Rees F
authors.initials: RF
authors.lastname: Garmann
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA.
authors.forename: Mauricio
authors.initials: M
authors.lastname: Comas-Garcia
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA.
authors.forename: Ajaykumar
authors.initials: A
authors.lastname: Gopal
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA.
authors.forename: Charles M
authors.initials: CM
authors.lastname: Knobler
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA; California NanoSystems Institute, and Molecular Biology Institute, University of California, Los Angeles, CA 90095, USA. Electronic address: gelbart@chem.ucla.edu.
authors.forename: William M
authors.initials: WM
authors.lastname: Gelbart
mesh_terms: D017795:Bromovirus / Q000502:physiology*; D036022:Capsid Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008854:Microscopy, Electron; D012367:RNA, Viral / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019065:Virus Assembly / Q000502:physiology*
chemical_list: D036022:Capsid Proteins; D012367:RNA, Viral
keywords: cowpea chlorotic mottle virus; packaging; self-assembly; ssRNA; virus-like particle