Intermediate-resolution crystal structure of the human adenovirus B serotype 3 fibre knob in complex with the EC2-EC3 fragment of desmoglein 2.

ABSTRACT

The cryo-electron microscopy (cryo-EM) structure of the complex between the trimeric human adenovirus B serotype 3 fibre knob and human desmoglein 2 fragments containing cadherin domains EC2 and EC3 has been published, showing 31 and 32 complexes. Here, the crystal structure determined at 4.5 Šresolution is presented with one EC2-EC3 desmoglein fragment bound per fibre knob monomer in the asymmetric unit, leading to an apparent 33 stoichiometry. However, in concentrated solution the 32 complex is predominant, as shown by small-angle X-ray scattering (SAXS), while cryo-EM at lower concentrations showed a majority of the 31 complex. Substitution of the calcium ions bound to the desmoglein domains by terbium ions allowed confirmation of the X-ray model using their anomalous scattering and shows that at least one binding site per cluster of calcium ions is intact and exchangeable and, combined with SAXS data, that the cadherin domains are folded even in the distal part that is invisible in the cryo-EM reconstruction.