Capsid conformational sampling in HK97 maturation visualized by X-ray crystallography and cryo-EM.
Maturation of the bacteriophage HK97 capsid from a precursor (Prohead II) to the mature state (Head II) involves a 60 A radial expansion. The mature particle is formed by 420 copies of the major capsid protein organized on a T = 7 laevo lattice with each subunit covalently crosslinked to two neighbors. Well-characterized pH 4 expansion intermediates make HK97 valuable for investigating quaternary structural dynamics. Here, we use X-ray crystallography and cryo-EM to demonstrate that in the final transition in maturation (requiring neutral pH), pentons in Expansion Intermediate IV (EI-IV) reversibly sample 14 A translations and 6 degrees rotations relative to a fixed hexon lattice. The limit of this trajectory corresponds to the Head II conformation that is secured at this extent only by the formation of the final class of covalent crosslinks. Mutants that cannot crosslink or EI-IV particles that have been rendered incapable of forming the final crosslink remain in the EI-IV state.
Gan
Lu
L
Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
Speir
Jeffrey A
JA
Conway
James F
JF
Lander
Gabriel
G
Cheng
Naiqian
N
Firek
Brian A
BA
Hendrix
Roger W
RW
Duda
Robert L
RL
Liljas
Lars
L
Johnson
John E
JE
D010582:Bacteriophage lambda / Q000737:chemistry; D002213:Capsid / Q000737:chemistry*; D003432:Cross-Linking Reagents / Q000494:pharmacology; D020285:Cryoelectron Microscopy / Q000379:methods*; D003460:Crystallization; D018360:Crystallography, X-Ray / Q000379:methods*; D004583:Electrons; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D011487:Protein Conformation; D017510:Protein Folding; D019065:Virus Assembly
D003432:Cross-Linking Reagents