title: The maturational refolding of the β-hairpin motif of equine infectious anemia virus capsid protein extends its helix α1 at capsid assembly locus.
abstract: A retroviral capsid (CA) protein consists of two helical domains, CA(N) and CA(C), which drive hexamer and dimer formations, respectively, to form a capsid lattice. The N-terminal 13 residues of CA refold to a β-hairpin motif upon processing from its precursor polyprotein Gag. The β-hairpin is essential for correct CA assembly but unexpectedly it is not within any CA oligomeric interfaces. To understand the β-hairpin function we studied the full-length CA protein from equine infectious anemia virus (EIAV), a lentivirus sharing the same cone-shaped capsid core as HIV-1. Solution NMR spectroscopy is perfectly suited to study EIAV-CA that dimerizes weaker than HIV-1-CA. Comparison between the wild-type (wt) EIAV-CA and a variant lacking the β-hairpin structure demonstrated that folding of the β-hairpin specifically extended the N terminus of helix α1 from Tyr(20) to Pro(17). This coil to helix transition involves the conserved sequence of Thr(16)-Pro(17)-Arg(18) (Ser(16)-Pro(17)-Arg(18) in HIV-1-CA). The extended region of helix α1 constituted an expanded EIAV-CA(N) oligomeric interface and overlapped with the HIV-1-CA hexamer-core residue Arg(18), helical in structure and pivotal in assembly. Therefore we propose the function of the maturational refolding of the β-hairpin in CA assembly is to extend helix α1 at the N terminus to enhance the CA(N) oligomerization along the capsid assembly core interface. In addition, NMR resonance line broadening indicated the presence of micro-millisecond exchange kinetics due to the EIAV-CA(N) domain oligomerization, independent to the faster EIAV-CA(C) domain dimerization.
authors.affiliation: Laboratory of Molecular Biophysics, NHLBI, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Kang
authors.initials: K
authors.lastname: Chen
authors.forename: Grzegorz
authors.initials: G
authors.lastname: Piszczek
authors.forename: Carol
authors.initials: C
authors.lastname: Carter
authors.forename: Nico
authors.initials: N
authors.lastname: Tjandra
mesh_terms: D000595:Amino Acid Sequence; D036022:Capsid Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017124:Conserved Sequence; D004926:Escherichia coli / Q000235:genetics; D015870:Gene Expression; D015497:HIV-1 / Q000737:chemistry / Q000235:genetics; D004860:Infectious Anemia Virus, Equine / Q000737:chemistry* / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D017510:Protein Folding; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D040681:Structural Homology, Protein; D014771:Virion / Q000737:chemistry* / Q000235:genetics; D019065:Virus Assembly
chemical_list: D036022:Capsid Proteins; D011994:Recombinant Proteins