question: What is the basic secondary structure of the variable domains of a typical antibody?
answer: The variable domains of heavy and light chains of antibodies consist of two β-sheets. The first one is composed of four strands, A, B, E and D, and the second one is composed of six strands, named A', G, F, C, C' and C''. The antigen binding site is formed by the inter-strand links BC, C′C″ and FG from each domain.