3qpr

HK97 Prohead I encapsidating inactive virally encoded proteaseHK97 Prohead I encapsidating inactive virally encoded protease

3qpr, resolution 5.20Å Show:Asymmetric Unit Biological Assembly Structural highlights 3qpr is a 7 chain structure with sequence from Bphk7. This structure supersedes the now removed PDB entry 3p8q. Full crystallographic information is available from OCA. For a guided tour on the structure components use FirstGlance. Related: 3p8q, 3e8k Gene: 5 (BPHK7) Experimental data: Check Resources: FirstGlance, OCA, PDBe, RCSB, PDBsum, ProSAT Publication Abstract from PubMed Virus capsid assembly requires recruiting and organizing multiple copies of protein subunits to form a closed shell for genome packaging that leads to infectivity. Many viruses encode scaffolding proteins to shift the equilibrium toward particle formation by promoting intersubunit interactions and stabilizing assembly intermediates. Bacteriophage HK97 lacks an explicit scaffolding protein, but the capsid protein (gp5) contains a scaffold-like N-terminal segment termed the delta domain. When gp5 is expressed in Escherichia coli, the delta domain guides 420 copies of the subunit into a procapsid with T=7 laevo icosahedral symmetry named Prohead-I. Prohead-I can be disassembled and reassembled under mild conditions and it cannot mature further. When the virally encoded protease (gp4) is coexpressed with gp5, it is incorporated into the capsid and digests the delta domain followed by autoproteolysis to produce the metastable Prohead-II. Prohead-I(+P) was isolated by coexpressing gp5 and an inactive mutant of gp4. Prohead-I and Prohead-I(+P) were compared by biochemical methods, revealing that the inactive protease stabilized the capsid against disassembly by chemical or physical stress. The crystal structure of Prohead-I(+P) was determined at 5.2 A resolution, and distortions were observed in the subunit tertiary structures similar to those observed previously in Prohead-II. Prohead-I(+P) differed from Prohead-II due to the presence of the delta domain and the resulting repositioning of the N-arms, explaining why Prohead-I can be reversibly dissociated and cannot mature. Low-resolution X-ray data enhanced the density of the relatively dynamic delta domains, revealing their quaternary arrangement and suggesting how they drive proper assembly. The Prohead-I Structure of Bacteriophage HK97: Implications for Scaffold-Mediated Control of Particle Assembly and Maturation.,Huang RK, Khayat R, Lee KK, Gertsman I, Duda RL, Hendrix RW, Johnson JE J Mol Biol. 2011 Jan 27. PMID:21276801 From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.