Cryo-EM structure of a bacteriophage T4 gp24 bypass mutant: the evolution of pentameric vertex proteins in icosahedral viruses.
ABSTRACT Many large viral capsids require special pentameric proteins at their fivefold vertices. Nevertheless, deletion of the special vertex protein gene product 24 (gp24) in bacteriophage T4 can be compensated by mutations in the homologous major capsid protein gp23. The structure of such a mutant virus, determined by cryo-electron microscopy to 26 angstroms, shows that the gp24 pentamers are replaced by mutant major capsid protein (gp23) pentamers at the vertices, thus re-creating a viral capsid prior to the evolution of specialized major capsid proteins and vertex proteins. The mutant gp23* pentamer is structurally similar to the wild-type gp24* pentamer but the insertion domain is slightly more distant from the gp23* pentamer center. There are additional SOC molecules around the gp23* pentamers in the mutant virus that were not present around the gp24* pentamers in the wild-type virus.
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ABSTRACT: The head of bacteriophage T4 is a prolate icosahedron with one unique portal vertex to which the phage tail is attached. The three-dimensional structure of mature bacteriophage T4 head has been determined to 22-A resolution by using cryo-electron microscopy. The T4 capsid has a hexagonal surface lattice characterized by the triangulation numbers T(end) = 13 laevo for the icosahedral caps and T(mid) = 20 for the midsection. Hexamers of the major capsid protein gene product (gp)23* and pentamers of the vertex protein gp24*, as well as the outer surface proteins highly antigenic outer capsid protein (hoc) and small outer capsid protein (soc), are clearly evident in the reconstruction. The size and shape of the gp23* hexamers are similar to the major capsid protein organization of bacteriophage HK97. The binding sites and shape of the hoc and soc proteins have been established by analysis of the soc(-) and hoc(-)soc(-) T4 structures.Proceedings of the National Academy of Sciences 05/2004; 101(16):6003-8. · 9.74 Impact Factor
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ABSTRACT: We have purified from T4 phage-infected cells an enzyme which cleaves purified prehead proteins to the size found in mature virions. Its specificity corresponds to that found in vivo since its action results in the creation of a new alanine amino-terminal on cleaved IPIII. We call this enzyme T4 prehead proteinase (T4PPase), because it acts on the proteins of the precursor to the T4 capsid. However, in vitro, the precursor proteins need not be assembled into a structure to be substrates for the enzyme. T4PPase requires neither an active serine nor a sulfhydryl group for activity. It is rapidly inactivated by autodigestion.Journal of Molecular Biology 11/1976; 107(1):35-54. · 3.91 Impact Factor
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ABSTRACT: Gene product (gp) 24 of bacteriophage T4 forms the pentameric vertices of the capsid. Using x-ray crystallography, we found the principal domain of gp24 to have a polypeptide fold similar to that of the HK97 phage capsid protein plus an additional insertion domain. Fitting gp24 monomers into a cryo-EM density map of the mature T4 capsid suggests that the insertion domain interacts with a neighboring subunit, effecting a stabilization analogous to the covalent crosslinking in the HK97 capsid. Sequence alignment and genetic data show that the folds of gp24 and the hexamer-forming capsid protein, gp23*, are similar. Accordingly, models of gp24* pentamers, gp23* hexamers, and the whole capsid were built, based on a cryo-EM image reconstruction of the capsid. Mutations in gene 23 that affect capsid shape map to the capsomer's periphery, whereas mutations that allow gp23 to substitute for gp24 at the vertices modify the interactions between monomers within capsomers. Structural data show that capsid proteins of most tailed phages, and some eukaryotic viruses, may have evolved from a common ancestor.Proceedings of the National Academy of Sciences 06/2005; 102(20):7163-8. · 9.74 Impact Factor