Dataset Information

Functional domains of the HK97 capsid maturation protease and the mechanisms of protein encapsidation.

ABSTRACT: Tailed double-stranded DNA bacteriophages and herpesviruses build capsids by co-assembling a major capsid protein with an internal scaffolding protein that then exits from the assembled structure either intact or after digestion in situ by a protease. In bacteriophage HK97, the 102-residue N-terminal delta domain of the major capsid protein is also removed by proteolysis after assembly and appears to perform the scaffolding function. We describe the HK97 protease that carries out these maturation cleavages. Insertion mutations at seven sites in the protease gene produced mutant proteins that assemble into proheads, and those in the N-terminal two-thirds were enzymatically inactive. Plasmid-expressed protease was rapidly cleaved in vivo but was stabilized by co-expression with the delta domain. Purified protease was found to be active during the assembly of proheads in vitro. Heterologous fusions to the intact protease or to C-terminal fragments targeted fusion proteins into proheads. We confirm that the catalytic activity resides in the N-terminal two-thirds of the protease polypeptide and suggest that the C-terminal one-fifth of the protein contains a capsid targeting signal. The implications of this arrangement are compared to capsid targeting systems in other phages, herpesviruses, and encapsulins.

SUBMITTER: Duda RL

PROVIDER: S-EPMC3709472 | biostudies-literature | 2013 Aug

REPOSITORIES: biostudies-literature

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Functional domains of the HK97 capsid maturation protease and the mechanisms of protein encapsidation.

Duda Robert L RL Oh Bonnie B Hendrix Roger W RW

Journal of molecular biology 20130517 15

Tailed double-stranded DNA bacteriophages and herpesviruses build capsids by co-assembling a major capsid protein with an internal scaffolding protein that then exits from the assembled structure either intact or after digestion in situ by a protease. In bacteriophage HK97, the 102-residue N-terminal delta domain of the major capsid protein is also removed by proteolysis after assembly and appears to perform the scaffolding function. We describe the HK97 protease that carries out these maturatio ...[more]

PMID: 23688818

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Project description:The herpesvirus capsid assembles in the nucleus as an immature procapsid precursor built around viral scaffold proteins. The event that initiates procapsid maturation is unknown, but it is dependent upon activation of the VP24 internal protease. Scaffold cleavage triggers angularization of the shell and its decoration with the VP26 and pUL25 capsid-surface proteins. In both the procapsid and mature angularized capsid, the apical region of the major capsid protein (VP5) is surface exposed. We investigated whether the VP5 apical region contributes to intracellular transport dynamics following entry into primary sensory neurons and also tested the hypothesis that conserved negatively charged amino acids in the apical region contribute to VP26 acquisition. To our surprise, neither hypothesis proved true. Instead, mutation of glutamic acid residues in the apical region delayed viral propagation and induced focal capsid accumulations in nuclei. Examination of capsid morphogenesis based on epitope unmasking, capsid composition, and ultrastructural analysis indicated that these clusters consisted of procapsids. The results demonstrate that, in addition to established events that occur inside the capsid, the exterior capsid shell promotes capsid morphogenesis and maturation.IMPORTANCE Herpesviruses assemble capsids and encapsidate their genomes by a process that is unlike those of other mammalian viruses but is similar to those of some bacteriophage. Many important aspects of herpesvirus morphogenesis remain enigmatic, including how the capsid shell matures into a stable angularized configuration. Capsid maturation is triggered by activation of a protease that cleaves an internal protein scaffold. We report on the fortuitous discovery that a region of the major capsid protein that is exposed on the outer surface of the capsid also contributes to capsid maturation, demonstrating that the morphogenesis of the capsid shell from its procapsid precursor to the mature angularized form is dependent upon internal and external components of the megastructure.

Dataset Information

Functional domains of the HK97 capsid maturation protease and the mechanisms of protein encapsidation.

Publications

Functional domains of the HK97 capsid maturation protease and the mechanisms of protein encapsidation.

Similar Datasets

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