Figure 1.

(A) Schematic representation of a conventional IgG antibody. Immunoglobulin G (IgG) have approximately 150 kDa and consist of two identical light chains (L) and two identical heavy chains (H) connected by disulfide bonds. Light chains are made up of a variable domain (VL) and a constant domain (CL). Heavy chains are made up of a variable domain (VH) and three constant domains (CH₁, CH₂ e CH₃). The IgG molecule can also be divided into two main fragments: the antigen-binding-domain (Fab) and the fragment crystallizable (Fc) domain. The Fab fragment consists of two constant domains (CH₁ and CL) and two variable domains (VH and VL). (B) Schematic representation of different antibody fragments. Fragment of antigen binding (Fab) composed of VL and a constant domain of the light chain (CL) linked to VH and a constant domain of the heavy chain (CH₁) by a disulfide bond between the CL and CH₁ domains. Single chain fragment variable (scFv) composed only of variable regions, one from the heavy chain (VH) and the other from the light chain (VL). The two variable regions are linked by a flexible glycine-serine linker (Gly₄Ser)₃. Camelid and shark immunoglobulin composed of only heavy chains. They present no light chain, and the displayed V domains bind their targets separately. Camelid heavy-chain antibodies composed a homodimer of one variable domain (VHH) and two C-like constant domains (CH). Shark new antigen receptor antibodies (IgNARs) composed of one variable domain (V-NAR) and five C-like constant domains (CH).