Fig. 2.

CryoEM map of the fiber tail and its interaction with the penton base. (a) Top view of the individual penton complex cut from the 4Å density map of Ad5 (Fig. 1a) showing the fiber (magenta) binding to penton base by its tails. The five penton-base monomers are shown in alternating colors cyan, yellow and green. (b) Side view of the fiber density segmented from (a). Five tail densities are visible due to the imposition of five-fold symmetry (left), but two positions (transparent) should be left unoccupied (right). (c) Penton complex showing five fiber-tail densities (magenta) attached to the penton-base pentamer. The fiber shaft density is removed for clarity. Lower inset: Enlargement of the black boxed region showing one fiber tail lying in the groove of two adjacent penton-base monomers. (d) Stereo view of the atomic model (sticks) of an α helix from the top surface of penton-base protein superimposed on its density (mesh). (e) Stereo view of our atomic model (sticks) of the fiber tail (aa7–19) superimposed on its densities (mesh). Three large and distinct side chains (Phe11, Tyr15 and Tyr17) are used as ‘landmarks’ for accurate registration of amino acids. (f) Stereo view of the fiber tail (sticks) inside the groove between two adjacent penton-base monomers (ribbon models, colored yellow and cyan respectively). The interactions between the fiber tail and the penton base include many hydrophobic interactions [side chains Met227, Pro228 and Tyr292 from one penton-base monomer and Leu193, Phe499 and His494 form the other monomer], two probable hydrogen bonds [dashed lines, between Glu203 (penton base) and Asn12 (fiber) and between His495 (penton base) and Tyr15 (fiber)] and one probable salt bridge [dashed lines, between Lys387 (penton base) and Asp18 (fiber)].