The basic structure of an antibody

The basic structure of an antibody consists of two identical “heavy” polypeptide chains paired with two identicalshorter “light” chains, forming an approximate, flxible Yshape (Fig. 1). The chains are subdivided into domainsconsisting of approximately 110 amino acids, which arelinked by a variable number of disulfie bonds, giving atotal molecular mass of approximately 150 kDa.IgG antibodies, the most abundant class of antibody inserum, consist of one Y unit. The IgG subclasses differmainly in the number of inter-heavy chain disulfie bonds.The CH and CL domains are relatively constant in sequence,with varying degrees of glycosylation, and are responsiblefor the effector functions of the antibody, i.e., its bindingto complement and cells involved in the immune response.The VH and VL domains, however, are more variable insequence. Within the variable regions of each chain, thereare three areas of hypervariable sequence, known ascomplementarity-determining regions (CDRs), eachforming a loop structure supported by a framework of βsheets (Fig. 2). The six CDRs on each arm of the antibody