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Proteolytic and conformational control of virus capsid maturation: the bacteriophage HK97 system.

Abstract：

:Bacteriophage capsid assembly pathways provide excellent model systems to study large-scale conformational changes and other mechanisms that regulate the formation of macromolecular complexes. These capsids are formed from proheads: relatively fragile precursor particles which mature by undergoing extensive remodeling. Phage HK97 employs novel features in its strategy for building capsids, including assembly without a scaffolding protein, and the formation of a network of covalent cross-links between neighboring subunits in the mature virion. In addition, proteolytic cleavage of the capsid protein from 42 kDa to 31 kDa is essential for maturation. To investigate the structural bases for proteolysis and cross-linking, we have used cryo-electron micrographs to reconstruct the three-dimensional structures of purified particles from four discrete stages in the assembly pathway: Prohead I, Prohead II, Head I and Head II. Prohead I has icosahedral T = 7 packing of blister-shaped pentamers and hexamers. The pentamers are 5-fold symmetric, but the hexamers exhibit an unusual departure from 6-fold symmetry, as if two trimers had undergone a shear dislocation of about 25 A. Proteolytic conversion to Prohead II leaves the outer surface largely unchanged, but a major loss of density from the inner surface is observed, which we infer to represent the excision of the amino-terminal domains of the capsid protein. Upon expansion to the Head I state, the capsid becomes markedly larger, thinner walled, and more polyhedral: moreover, the capsomer shapes change radically; especially notable is the disappearance of the large hexon dislocation. No differences between Head I and the covalently cross-linked Head II could be observed at the current resolution of about 25 A, from which we infer that it is the conformational rearrangements effected by expansion that create the micro-environments needed for the autocatalytic formation of the isodipeptide bonds found in the mature virions ("pseudo-active sites").

journal_name

J Mol Biol

journal_title

Journal of molecular biology

authors

Conway JF,Duda RL,Cheng N,Hendrix RW,Steven AC

doi

10.1006/jmbi.1995.0538

subject

Has Abstract

pub_date

1995-10-13 00:00:00

pages

86-99

issue

eissn

0022-2836

issn

1089-8638

pii

S0022-2836(85)70538-4

journal_volume

253

pub_type

杂志文章

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Proteolytic and conformational control of virus capsid maturation: the bacteriophage HK97 system.