PMID:26616586

Citation	Huet, A, Duda, RL, Hendrix, RW, Boulanger, P and Conway, JF (2016) Correct Assembly of the Bacteriophage T5 Procapsid Requires Both the Maturation Protease and the Portal Complex. J. Mol. Biol. 428:165-81
Abstract	The 90-nm-diameter capsid of coliphage T5 is organized with T=13 icosahedral geometry and encloses a double-stranded DNA genome that measures 121kbp. Its assembly follows a path similar to that of phage HK97 but yielding a larger structure that includes 775 subunits of the major head protein, 12 subunits of the portal protein and 120 subunits of the decoration protein. As for phage HK97, T5 encodes the scaffold function as an N-terminal extension (∆-domain) to the major head protein that is cleaved by the maturation protease after assembly of the initial prohead I form and prior to DNA packaging and capsid expansion. Although the major head protein alone is sufficient to assemble capsid-like particles, the yield is poor and includes many deformed structures. Here we explore the role of both the portal and the protease in capsid assembly by generating constructs that include the major head protein and a combination of protease (wild type or an inactive mutant) and portal proteins and overexpressing them in Escherichia coli. Our results show that the inactive protease mutant acts to trigger assembly of the major head protein, probably through binding to the ∆-domain, while the portal protein regulates assembly into the correct T=13 geometry. A cryo-electron microscopy reconstruction of prohead I including inactivated protease reveals density projecting from the prohead interior surface toward its center that is compatible with the ∆-domain, as well as additional internal density that we assign as the inactivated protease. These results reveal complexity in T5 beyond that of the HK97 system.
Links	PubMed PMC4738002 Online version:10.1016/j.jmb.2015.11.019
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
9CAUD:A0A0K2D089		GO:0046798: viral portal complex	ECO:0000315:		C		The authors use mutations in both protease and portal complex to determine their roles in capsid assembly. Figures 2 and 5 show that inactivated portal protein does not give rise to correct capsid assembly and allow DNA packaging.	complete CACAO 11424
BPT5:PORTL		GO:0039710: cytoplasmic icosahedral capsid assembly	ECO:0000314:		P		Figure 2	complete CACAO 11486
BPT5:PRO		GO:0019069: viral capsid assembly	ECO:0000315:		P		Mixture of pb11 affected the migration of pb8p (Fig 3a) so pb11 interacts with pb8p; this interaction induces production of prohead like particles (Fig 3b). Experiments reveal that light scattering increases with higher pb11 concentration because of the density of the formed capsid and tube particles (Fig 4a, 4c, 4d). Also shown is pb8p amount being inversely proportional to pb11 amount (Fig 4b) supporting pb11 interaction and capsid assembly role.	complete CACAO 12895

References

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