Role of interfacial amino acid residues in assembly, stability, and conformation of a spherical virus capsid.
Twenty-eight amino acid residues involved in most noncovalent interactions between trimeric protein subunits in the capsid of the parvovirus minute virus of mice were truncated individually to alanine, and the effects on capsid assembly, thermostability, and conformation were analyzed. Only seven side chains were essential for protein subunit recognition. These side chains virtually corresponded with those that either buried a large hydrophobic surface on trimer association or formed buried intertrimer hydrogen bonds or salt bridges. The seven residues are evolutionarily conserved, and they define regularly spaced spots on a thin equatorial belt surrounding each trimer. Truncation of the many side chains that were dispensable for assembly, including those participating in solvent-accessible polar interactions, did not substantially affect capsid thermostability either. However, the interfacial residues located at the base of the pores delineating the capsid five-fold axes participated in a heat-induced conformational rearrangement associated with externalization of the capsid protein N terminus, and they were needed for infectivity. Thus, at the subunit interfaces of this model virus capsid, only key residues involved in the strongest interactions are critical for assembly and stability, but additional residues fulfill other important biological roles.
Reguera
Juan
J
Centro de Biología Molecular Severo Ochoa (CSIC-UAM), Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid, Spain.
Carreira
Aura
A
Riolobos
Laura
L
Almendral
José María
JM
Mateu
Mauricio G
MG
D019943:Amino Acid Substitution; D000596:Amino Acids / Q000737:chemistry*; D000818:Animals; D001665:Binding Sites; D036022:Capsid Proteins / Q000737:chemistry*; D002460:Cell Line; D051379:Mice; D008915:Minute Virus of Mice / Q000737:chemistry* / Q000472:pathogenicity; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry
D000596:Amino Acids; D036022:Capsid Proteins; D011994:Recombinant Proteins; C095548:capsid protein VP2, parvovirus B19