Bacteriophage HK97 capsid assembly is a premier model system for studying aspects of protein assembly mechanisms. Maturation of the head protein of HK97 includes interesting interactions with chaperonins, assembly into interconvertible hexamers and pentamers, assembly into Prohead I together with portal and protease proteins, cleavage of the head protein and protease within the interior of the structure to create a new intermediate, Prohead II, expansion and interlinking of protein subunit chains, and the formation of novel covalent inter-peptide crosslinks.

The HK97 head is assembled from minor proteins gp3 (47 kDa), gp4 (25kDa), and the major head protein, gp5 (42kDa). The initial steps require the host chaperones GroEL & GroES and ATP. Prohead I is the first large intermediate and is converted to Prohead II when gp5 is cleaved from 42kDa to 31kDa under the control of gp4. The portion of gp5 that is lost is called the delta region and lies inside the shell. Prohead II will mature and expand into a mature Head, usually at the time of DNA packaging. During expansion, reactive sites are created that cross-link gp5 subunits to adjacent subunits until all of the subunits are crosslinked in Head II. The above surface rendered images are colorized versions of images made by James Conway from micrographs taken by Naiqian Cheng - see collaborations and J.Mol. Biol. 253: 86-99.

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Capsid conformational sampling in HK97 maturation visualized by X-ray crystallography and cryo-EM.

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Control of crosslinking by quaternary structure changes during bacteriophage HK97 maturation.

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Crystallization and preliminary analysis of a dsDNA bacteriophage capsid intermediate: Prohead II of HK97.

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An elastic network model of HK97 capsid maturation.

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The refined structure of a protein catenane: the HK97 bacteriophage capsid at 3.44 A resolution.

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Virus maturation involving large subunit rotations and local refolding.

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High-temperature protein mass mapping using a thermophilic protease.

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Topologically linked protein rings in the bacteriophage HK97 capsid.

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Maturation dynamics of a viral capsid: visualization of transitional intermediate states.

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Genomic sequences of bacteriophages HK97 and HK022: pervasive genetic mosaicism in the lambdoid bacteriophages.

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Crystallization and preliminary X-ray analysis of the dsDNA bacteriophage HK97 mature empty capsid.

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