Schematic representation of Ig-domains dimerization patterns and contact network A) VH:VL schematic parallel interface and conserved interactions B) CH1:CL schematic antiparallel interface and conserved interactions (see text).

On the left a schematic representation of the domain interface with the C2 pseudo symmetry axis. Note that the symmetry axis for VH:VL is vertical corresponding to a parallel interface, while it is horizontal for CH1:CL as the interface is antiparallel. On the right the residue interaction network. Residue subscripts indicate the percentage of occurrence of that residue at that position, if less than 100% in the dataset. Ig strands are color-coded according to the iCn3D IgStrand scheme (See Methods). Only residue-residue interactions present in 70% of the Fabs in each dataset are shown with solid lines. Dotted lines with a % number represent interactions that are present in at least 70% of the Fabs in the diverse antigen binding dataset, with the % number representing the % of Fabs in which this contact is present in the SARS-CoV-2 antigen binding dataset. Interaction lines between residues in VH:VL and CH1:CL domains are color-coded in red for symmetric contacts, green line for hydrogen bonds and purple for a noticeable conserved ionic interaction in CH1:CL; otherwise, grey indicates van der Waals interactions. The highly common interactions, present in at least 90% of the dataset, are indicated by a star. See Tables 2 and 3 for more details. The VH:VL and CH1:CL interfaces of a specific Fab (PDBid:7LM8) can be visualized and analyzed with the iCn3D link: https://www.ncbi.nlm.nih.gov/Structure/icn3d/share.html?uvawHK16NinhaZL68.