Volume 17, Issue 6, Pages 800-808 (June 2009) The Structure of Gene Product 6 of Bacteriophage T4, the Hinge-Pin of the Baseplate  Anastasia A. Aksyuk, Petr G. Leiman, Mikhail M. Shneider, Vadim V. Mesyanzhinov, Michael G. Rossmann  Structure  Volume 17, Issue 6, Pages 800-808 (June 2009) DOI: 10.1016/j.str.2009.04.005 Copyright © 2009 Elsevier Ltd Terms and Conditions

Figure 1 Ribbon Diagram of Gp6_334C Stereo view of the structure is shown with domains I, II, and III colored in blue, red, and gold, respectively. Loops I and II of domain II are colored in cyan. Also shown is the linear scheme of the domain positions in the amino acid sequence using the same color code. Structure 2009 17, 800-808DOI: (10.1016/j.str.2009.04.005) Copyright © 2009 Elsevier Ltd Terms and Conditions

Figure 2 Ribbon Diagrams of the Gp6_334C Dimer One monomer is colored in magenta, the other in blue. Three views related by a 90° rotation are shown. Structure 2009 17, 800-808DOI: (10.1016/j.str.2009.04.005) Copyright © 2009 Elsevier Ltd Terms and Conditions

Figure 3 Structure of the Gp6 Ring as Found Before (Left) and After (Right) Bacteriophage Infection Each panel shows the baseplate as viewed down the six-fold axis from the distal end of the tail. The monomers in the C-terminal dimers found in the crystal structure are shown in the same color. These dimeric interactions connect neighboring wedges together. (A) Fit of the gp6_334C structure in the dome-shaped (left) and star-shaped (right) conformations of the baseplate. (B) Closer view of the fit for each conformation. Density corresponding to the outer proteins was zeroed out and only the density corresponding to the inner baseplate proteins (gp6, gp53 and gp53) is shown. (C) A schematic drawing of the ring rearrangement is shown with the flexible linkers between the N- and C-terminal domains of gp6 indicated by arrows. Circles show two types of dimeric interactions that are preserved throughout the baseplate rearrangement. Diameter of the ring and the wedge borders are indicated by black dashed lines. Structure 2009 17, 800-808DOI: (10.1016/j.str.2009.04.005) Copyright © 2009 Elsevier Ltd Terms and Conditions

Figure 4 Arrangement of Gp6, Gp53, and Gp25 Arrangement of gp6, gp53, and gp25 in the dome-shaped (left) and star-shaped (right) baseplate (A) Densities corresponding to gp6, gp53, and gp25 are shown. The whole of gp6 is shown in magenta for the dome-shaped baseplate (left) and in blue for the star-shaped baseplate (right). The C-terminal part of gp6 corresponds to the crystal structure and is shown as Cα trace with spheres representing each residue. The N-terminal part of gp6 was segmented from the cryo-EM map. The densities corresponding to gp53 and gp25 are shown in white. (B) The densities of gp53 and gp25 after the density for the whole of gp6 was zeroed out. (C) The N-terminal gp6 dimers as found in the baseplate wedge. The C-terminal domain is shown as a Cα trace, whereas the N-terminal domain, for which the structure remains unknown, is shown as a density mesh. (D) The segmented envelope of gp6 monomers. In the middle panel, the C-terminal domains were superimposed to show the hinge angle change between the N- and C-terminal domains of gp6 in the dome-shaped (magenta) and star-shaped (blue) baseplate. (E) The segmented gp53 and gp25 densities, with gp25 shown in dark gray and gp53 in white. Structure 2009 17, 800-808DOI: (10.1016/j.str.2009.04.005) Copyright © 2009 Elsevier Ltd Terms and Conditions

Figure 5 Structure of the Baseplate Wedge (A) The stereo diagram of the wedge as found in the dome-shaped baseplate. (B) Schematic of the interactions of proteins within a wedge. (C) Interactions between two wedges in the assembled baseplate. Gp9, gp12, gp54, and gp48 bind to the baseplate after the six wedges have assembled around the hub. Structure 2009 17, 800-808DOI: (10.1016/j.str.2009.04.005) Copyright © 2009 Elsevier Ltd Terms and Conditions

Figure 6 Interactions of Gp6 with Other Proteins Interactions of gp6 with other proteins in the dome-shaped (left) and star-shaped (right) baseplate. (A) Gp6, gp53, gp25, gp18, and gp48 (left only) in two neighboring wedges are colored in coral, white, gray, green, and violet, respectively. Gp6, gp48, and gp53 make a binding site for gp18 (left) and the interactions change in the star-shaped conformation (right). (B) The dimer of gp6 with residues involved in binding to other proteins colored by the physical properties of amino acids with hydrophobic residues in yellow, positively charged in blue, negatively charged in red, and polar in cyan. The gp8 binding site is circled in blue, gp7 in red, and gp53 in light gray. (C) Schematic of the interactions between several baseplate proteins in the dome-shaped (left) and star-shaped (right) conformations of the baseplate. The interactions of gp6 with gp8 and gp7 are indicated by arrows. In the star-shaped baseplate (right), gp8 remains bound to gp7, but is no longer bound to gp6. The change in the interactions between gp7 and gp6 results in the change of hinge angle between the N- and C-terminal domains of gp6. Structure 2009 17, 800-808DOI: (10.1016/j.str.2009.04.005) Copyright © 2009 Elsevier Ltd Terms and Conditions

Figure 7 The Two Types of Gp6 Dimers (A) A stereo view of the four neighboring gp6 molecules from the two neighboring wedges of the dome-shaped baseplate. Six gp6 dimers, with the two monomers colored in red and blue, form the ring of gp6. Each gp6 molecule forms two types of dimers, corresponding to an intrawedge, N-terminal dimer and interwedge C-terminal dimer. The N-terminal part of gp6 is shown as a density mesh and the C-terminal part corresponds to the crystal structure. (B) Schematic of the four gp6 monomers using the same colors as in (A). The N-terminal part is shown as a triangle and the C-terminal part as a rectangle. Structure 2009 17, 800-808DOI: (10.1016/j.str.2009.04.005) Copyright © 2009 Elsevier Ltd Terms and Conditions