HK97 BACTERIOPHAGE PROHEADS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Bacteriophage HK97 is a lambda-like, tailed dsDNA bacteriophage that has emerged as a highly accessible model system for studies of particle assembly and maturation. This system allows a number of intermediate particle states to be isolated and characterized and hence provides excellent opportunities for detailed structural and biophysical analysis of complex macromolecular assembly. The HK97 prohead is composed of 420 copies of a 42kDa capsid protein that assemble into an T=7l icosahedral shell, called Prohead-I. Approximately 60 copies of the phage-encoded protease are packaged into the Prohead-I shell during assembly. After the capsid is formed, the protease cleaves off residues 2-103, called the ∆-domain, from the capsid proteins. The ∆-domain is a scaffolding protein and a crucial component for directing the capsid subunits to assemble into an icosahedral particle. After proteolysis, the resulting particle, called Prohead-II, resembles Prohead-I on the exterior, however the interior surface has been completely remodeled as a result of removal of the ∆-domains. Prohead-II enters the maturation cascade by capsid expansion and intersubunit crosslinking. In this proposal, we seek to determine a high resolution atomic structure of Prohead-I and Prohead-II by X-ray crystallography. The structure will allow us to compare subunit conformations and inter/intra capsomer interactions in the proheads with organizations previously observed in mature capsid states. A detailed structure will also help us to fully understand the determinants of virus assembly and the biophysical mechanism of capsid maturation.