The typical organization of the VHH domain is represented using the structure of a VHH to carbazol (PDB 1U0Q)

The typical organization of the VHH domain is represented using the structure of a VHH to carbazol (PDB 1U0Q). of the analyte, the exquisite specificity of antibody recognition allows the detection of trace amounts of the target analyte even in highly complex matrices. This principle of immunodetection was first demonstrated in 1959 when Berson and Yalow developed the first radioimmunoassay for human insulin using a guinea pig antiserum (1). A Episilvestrol second major milestone occurred in 1975 when Khler and Milstein developed the hybridoma technology, enabling the production of high quantities of monoclonal antibodies of the desired specificity (2). Interesting, these two Nobel Prize winning achievements were Rabbit Polyclonal to PPIF not patented, which contributed highly to the widespread use of antibodies for immunodetection assays. Further progress in molecular biology and the genetics of antibody diversity added new venues for antibody discovery, with higher control on the selection process and new engineering possibilities (35). This paved the way for the current bloom of therapeutic applications of Episilvestrol antibodies but also provided the technology to create new assays and biosensors based on the use of recombinant antibody fragments that could be easily tagged and produced at low cost by microbial fermentation (6,7). All this progress has been dominated by the use of conventional hetero tetrameric antibodies, prototypically represented by the IgG molecule and its fragments (Figure1), but more recently, the recombinant binding domain of a special type of antibodies devoid of light chain have emerged as a salient alternative for immunosensing. Here, we first present an overview of the heavy-chain-only antibodies (HcAbs) and then outline the characteristics that make them to stand out as unique analytical and diagnostic tools. == Figure 1. == Schematic representation of conventional and heavy-chain-only antibodies (HcAbs). Conventional antibodies, formed by heavy (cyan) and light (blue) chains, are found in all vertebrate, but camelids and cartilaginous fish also have antibodies devoid of light chain, whose antigen-binding site sits exclusively in the heavy chain variable domain. The organization of the heavy chain variable domain of each of these antibodies is shown using three representative structures [PDB IDs: 5WT9 (VH); 5TP3 (VHH); and 2COQ (V-NAR)]. CDR1, CDR2, and CDR3 are depicted in orange, green, and red, respectively, except for V-NAR that lacks CDR2, and the green color is used to denote the HV4 region that sometimes participates in antigen binding. VHHs and V-NARs usually have long CDR3 and non-canonical disulfide bridges (yellow). While the antigen-binding site of conventional antibodies is formed by the combination of the six CDRs of the heavy and light chain, only three and two CDRs are involved in the formation of binding site of camelid and shark HcAb, respectively. Notice that HcAbs do not have the CH1 or an equivalent domain, which forms a strong interaction with the constant domain of the light chain in conventional antibodies. == Camelids and Sharks have a Special Type of Antibodies Devoid of Light Chain == In 1993 researchers from the Vrije University in Brussel reported the existence of a special type of antibodies in camels that were devoid of light chain (8). These, so-called, HcAbs account for up to 5080% of the circulating antibodies in camels and were also found to be present in the serum of the South American camelids, though in lower concentration (1125%) (9,10). Camelid HcAbs have a typical IgG Episilvestrol Fc region with dedicated isotypes (IgG2 and IgG3) but lack the CH1 constant domain and have a distinctive variable domain (VHH) with structural features that increase its solubility (Figure1). Other than camelids, HcAb have not been found in other organisms, with the curious exception of sharks and other cartilaginous fish (Chondrichthyes), the oldest living beings with.