(a) The Fab molecules in both the CLL183 and CLL240 crystals interact through VH CDR3-dominated contacts. The heavy and light chains of the Fab acting as ‘receptor’ are coloured light blue and pink, with the VH CDR3 loop highlighted in red. The chains in the ‘antigen’ molecule are coloured blue and cyan (VH and CH1 domains), and violet and magenta (VK and CK), respectively. (b) Molecular surface of the epitope, with the amino acids from VH CDR3 involved in the binding interactions shown as sticks coloured as in the previous panel. Parts of the structure have been omitted for clarity.