Fig. 4: Milano baseplate centerpiece (BCP) connects tail, baseplate and central spike.

a Baseplate wedge attached to the central spike assembly. The baseplate centerpiece (BCP, gp25) of Milano is shown in the yellow ribbon model. The tube (gp21), baseplate hub (BH, gp26) and baseplate central spike (BCS, gp27) are colored gray. The baseplate wedge 1 (BW1, gp28), 2 (BW2, gp29) and 3 (BW3, gp30) are colored red, pink, and orange, respectively. The N-terminal tube domain of BCP connects the tail-tube to the baseplate hub. The middle helical domain of BCP is embedded into the groove of the baseplate wedge. b Comparison of Milano BCP (yellow) domains with its structural homologs in bacteriophages T4 (gray) and A511 (white). c The middle helical domain of Milano BCP (yellow ribbon) is embedded into the groove of the baseplate wedge (surface representation, BW1, red; BW2, pink; BW3, orange). d Structure of baseplate hub (BH) and baseplate central spike (BCS). Representative subunit is colored blue-to-red from N- to C-terminus. e Structure of BW1, BW2, BW3, and baseplate wedge asymmetric unit (ASU) with highlighted Cys residues involved in intra-ASU (yellow sphere) and inter-ASU (red sphere) disulfide bonds. Two conformations of BW2 protein are shown superimposed. f The side, bottom, and top views of baseplate wedge assembly formed by six baseplate wedge ASUs.