The neck of bacteriophage T4 is a ring-like structure formed by a hetero-oligomer of gp13 and gp14

doi:10.1016/j.bbapap.2007.05.011

Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics

Volume 1774, Issue 8, August 2007, Pages 1036-1043

https://doi.org/10.1016/j.bbapap.2007.05.011 Get rights and content

Abstract

After packaging of DNA into the head of bacteriophage T4 is completed, a neck is formed at the portal vertex of the head to be ready for the tail attachment. The main components of the neck are gp13 and gp14 (gp: gene product), which consist of 309 and 256 amino acid residues, respectively. In order to elucidate the structure and subunit arrangement in the neck, overexpression systems of gene 13 and gene 14 were constructed and purified to homogeneity. Far-UV circular dichroism (CD) spectra of gp13 and gp14 indicated that gp13 is rich in α-helices whereas gp14 is rich in β-sheets. Sedimentation velocity analysis of gp13 and gp14 revealed that both proteins are present as monomers in solution. The frictional ratios (f/f₀) of the two proteins indicated that gp14 has a more elongated shape than gp13. Although isolated gp13 and gp14 do not interact with each other when mixed under physiological conditions, they form a hetero-oligomer complex with the stoichiometry of 10:5 after treatment with ammonium sulfate. Electron microscopy of this complex has shown that it forms a ring-like structure of 15 nm in diameter.

Introduction

Bacteriophage T4 is a member of the Myoviridae family which infects the host bacterium Escherichia coli. The self-assembly pathway of the virion has been extensively investigated as reviewed by a number of authors [1], [2], [3]. The phage head, tail and tail fibers assemble independently along well-ordered pathways and after the head and tail join, the tail fibers bind to the tail to form an infectious virion. The head of phage T4 is a prolate icosahedron which is 120 nm long and 86 nm wide in diameter [4]. The prohead formation is initiated by the initiator complex made of twelve subunits of gp20 which form the portal vertex [5]. The genomic DNA of phage T4 is packaged through the portal vertex into the head after the prohead assembly is completed. Before or during the DNA packaging, expansion of the prohead occurs, resulting in a volume increase of about 50% [6]. Upon completion of the DNA packaging, the attachment of gp13 and gp14 to the portal vertex takes place before the tail joining begins [7], [8].

In another pathway, tail tube and the sheath polymerization are terminated by gp3 and gp15. Gp3 binds at the proximal end to the tube, forming a hexameric ring structure and stopping tube polymerization [2], [9]. The connector protein, gp15, then binds to gp3 and the sheath and forms the connector which protrudes from the top of the sheath by about 6–8 nm [2], [7], forming a hexameric ring of 13 nm in diameter [10]. Gp13 and/or gp14 recognize gp15, leading to the joining of the head and the tail.

The structure and the subunit composition of the neck were first studied by Coombs and Eiserling [7]. They observed the “necked” tail by electron microscopy with negative staining. The “necked” tail can be obtained by osmotic shock upon rapid dilution of T4 phage solution from 1.58 M CsCl to a buffer without CsCl, which disrupts the head and yields a tail with a neck [7]. They reported that the neck is 15 nm in length and 16 nm in width and is located between the portal vertex gp20 and the connector protein gp15. Six fibers called whiskers or fibritin, formed by gpwac, are attached to the neck. There are six protein components between the head and tail of which the major structural components are gpwac, gp13 and gp14. Genes wac, 13 and 14 are present in this order in the phage genome following the baseplate gene cluster and regulated by a common promoter.

Recently, the structure of the tail including the neck was analyzed by three-dimensional image reconstruction from cryo-electron microscopy to a resolution of 15 Å [11], [12], which is not sufficient for the subunit arrangement in the neck region to be discernible. In order to elucidate the structure and interactions of the neck proteins, gene 13 and 14 were cloned and overexpressed. The gene products were purified to homogeneity and the proteins were characterized by analytical ultracentrifugation, circular dichroism and electron microscopy with negative staining. In the present study it is shown that ammonium sulfate induced a specific interaction between gp13 and gp14 to form a hetero-oligomer whose dimension appears consistent with binding to the gp15 connector.

Section snippets

Bacterial strains and plasmid

E. coli XL1-blue was used for the construction of plasmids. E. coli BL21 (DE3) was used for overexpression. Expression vectors pET29a and pET28b (Novagen) were used for cloning of gene 13 and gene 14 respectively.

Media, chemicals and buffers

LB broth contains 1% (w/v) Bacto Tryptone, 0.5% (w/v) Bacto yeast extract and 0.5% (w/v) NaCl. LB plate contains 1% (w/v) Bacto Trypton, 0.5% (w/v) Bacto yeast extract, 1% (w/v) Bacto agar and 1% (w/v) NaCl. T-buffer had a final concentration of 50 mM Tris pH 8.0. TE-buffer was

Purification of gp13 and gp14

Genes 13 and 14, which encode neck proteins, were cloned in expression vectors as described in Materials and methods. The expressed proteins were purified by ammonium sulfate fractionation, ion exchange, hydrophobic, and gel filtration chromatography to near homogeneity (95%) as shown in Fig. 1. The molecular weights of purified gp13 (Fig. 1, lane 3) and gp14 (Fig. 1, lane 1) were about 35,000 and 32,000, respectively, which are in agreement with the calculated molecular weights of 34,745 and

Discussion

In the present study, genes 13 and 14, the major neck genes of phage T4, were cloned individually and the gene products were overexpressed. It was found that the individually expressed and purified gp13 and gp14 are monomers in solution and that they did not interact with each other under the physiological conditions investigated here. However, they can form a distinct complex when treated with ammonium sulfate. Only (gp13)₁₀(gp14)₅ complex was observed by sedimentation velocity (Fig. 4D) and

Acknowledgements

This work was supported by a Human Frontier Science Program grant (RGP-28/200) to Michael G. Rossmann, F.A., and Vadim V. Mesyanzhinov; and in part by a Grant-in-Aid for Scientific Research on Priority Areas (No. 16087204), Scientific Research (C) (No. 18570147) to F.A. and a Grant-in-Aid for Young Scientists (A) (No.17687014) to S.K. from the Ministry of Education, Culture, Sports, Science, and Technology of Japan.

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The neck of bacteriophage T4 is a ring-like structure formed by a hetero-oligomer of gp13 and gp14

Abstract

Introduction

Section snippets

Bacterial strains and plasmid

Media, chemicals and buffers

Purification of gp13 and gp14

Discussion

Acknowledgements

J. Mol. Biol.

J. Mol. Biol.

J. Mol. Biol.

J. Mol. Biol.

Cell

Anal. Biochem.

Biophys. J.

Biophys. J.

J. Struct. Biol.

Morphogenesis of bacteriophage T4 in extracts of mutant-infected cells

Proc. Natl. Acad. Sci. U. S. A.

Molecular architecture of the prolate head of bacteriophage T4

Proc. Natl. Acad. Sci. U. S. A.