PMID:23688818

Citation	Duda, RL, Oh, B and Hendrix, RW (2013) Functional domains of the HK97 capsid maturation protease and the mechanisms of protein encapsidation. J. Mol. Biol. 425:2765-81
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.
Links	PubMed PMC3709472 Online version:10.1016/j.jmb.2013.05.002
Keywords	Bacteriophages/enzymology; Bacteriophages/genetics; Bacteriophages/physiology; Capsid Proteins/metabolism; Catalytic Domain; DNA Mutational Analysis; Mutagenesis, Insertional; Peptide Hydrolases/genetics; Peptide Hydrolases/metabolism; Protein Processing, Post-Translational; Protein Sorting Signals; Protein Structure, Tertiary; Proteolysis; Virus Assembly
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
9CAUD:A0A0K2D0H8		GO:0006508: proteolysis	ECO:0000315:		P		The authors use linker insert mutant and frameshift on protease gene. As the results, (Shown in Fig 2) mutant genes are not able to perform proteolysis and protease requires specific spanning residues on the target polypeptide to incorporate into prohead.	complete CACAO 11430
BPHK7:PRO		GO:0019082: viral protein processing	ECO:0000315:		P		The authors use linker insert mutant and frameshift on protease gene. As the results, (Shown in Fig 2) mutant genes are not able to perform proteolysis and protease requires specific spanning residues on the target polypeptide to incorporate into prohead.	complete CACAO 11492

References

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