Heavy-chain antibodyheavy chain antibody size, heavy chain antibody
A heavy-chain antibody is an antibody which consists only of two heavy chains and lacks the two light chains usually found in antibodies
In common antibodies, the antigen binding region consists of the variable domains of the heavy and light chains VH and VL Heavy-chain antibodies can bind antigens despite having only VH domains This observation has led to the development of a new type of antibody fragments with potential use as drugs, so-called single-domain antibodies
- 1 Discovery
- 2 In cartilaginous fishes
- 3 In camelids
- 4 References
- 5 External links
In 1989 a group of biologists led by Raymond Hamers at the Free University Brussels investigated the immune system of dromedaries In addition to the expected four-chain antibodies, they identified simpler antibodies consisting only of two heavy chains This discovery was published in Nature in 1993 In 1995 a research team at the University of Miami found a different type of heavy-chain antibodies in sharks
In cartilaginous fishesA heavy-chain shark antibody left and a heavy-chain camelid antibody middle in comparison to a common antibody right Heavy chains are shown in a darker shade, light chains in a lighter shade
The immunoglobulin new antigen receptor IgNAR of cartilaginous fishes for example sharks is a heavy-chain antibody IgNAR shows significant structural differences to other antibodies It has five constant domains CH per chain instead of the usual three, several disulfide bonds in unusual positions, and the complementarity determining region 3 CDR3 forms an extended loop covering the site which binds to a light chain in other antibodies These differences, in combination with the phylogenetic age of the cartilaginous fishes, have led to the hypothesis that IgNAR could be more closely related to a primordial antigen-binding protein than the mammalian immunoglobulins To test this hypothesis, it would be necessary to discover IgNAR or similar antibodies in vertebrates that are phylogenetically still older, like the jawless fish lamprey and hagfish Non-vertebrates do not have antibodies at all
Sharks, and possibly other cartilaginous fishes, have immunoglobulin M IgM and immunoglobulin W IgW as well, both types with two heavy and two light chains
The only mammals with heavy-chain IgG-like antibodies are camelids such as dromedaries, camels, llamas and alpacas This is a secondary development: The heavy chains of these antibodies have lost one of their constant domains CH1 and underwent modifications in the variable domain VH, both structural elements necessary for the binding of light chains In one subgroup, the missing CH1 seems to be replaced by an extended hinge region, as shown in the image Despite their different overall structure, camelid heavy-chain antibodies share several properties with IgNAR, for example the extended CDR3 loop and the conformation of the CDR1 It has been reasoned that these similarities are caused by functional requirements, or convergent evolution, rather than a genuine relationship
About 50% of the antibodies in camelids are of the ordinary mammalian heavy/light-chain type It is not known whether any type of animal has only heavy-chain antibodies and completely lacks the common type with two heavy and two light chains
Heavy-chain camelid antibodies have been found to be just as specific as a regular antibody and in some cases they are more robust As well, they are easily isolated using the same phage panning procedure used for traditional antibodies, allowing them to be cultured ex vivo in large concentrations The smaller size and single domain make these antibodies easier to transform into bacterial cells for bulk production, making them ideal for research purposes
- ^ a b Harmsen, M M; Haard, H J 2007 "Properties, production, and applications of camelid single-domain antibody fragments" Applied Microbiology and Biotechnology 77 1: 13–22 doi:101007/s00253-007-1142-2 PMC 2039825 PMID 17704915
- ^ a b Hamers-Casterman, C; Atarhouch, T; Muyldermans, S; Robinson, G; Hamers, C; Songa, EB; Bendahman, N; Hamers, R 3 June 1993 "Naturally occurring antibodies devoid of light chains" Nature 363 6428: 446–8 Bibcode:1993Natur363446H doi:101038/363446a0 PMID 8502296
- ^ Greenberg, AS; Avila, D; Hughes, M; Hughes, A; McKinney, EC; Flajnik, MF 1995 "A new antigen receptor gene family that undergoes rearrangement and extensive somatic diversification in sharks" Nature 374 6518: 168–173 Bibcode:1995Natur374168G doi:101038/374168a0 PMID 7877689
- ^ a b Stanfield, R; Dooley, H; Flajnik, M; Wilson, I 2004 "Crystal structure of a shark single-domain antibody V region in complex with lysozyme" Science 305 5691: 1770–1773 Bibcode:2004Sci3051770S doi:101126/science1101148 PMID 15319492
- ^ Flajnik, M F; Dooley, H 2009 "The Generation and Selection of Single-Domain, V Region Libraries from Nurse Sharks" Methods in Molecular Biology Methods in Molecular Biology 562: 71–82 doi:101007/978-1-60327-302-2_6 ISBN 978-1-60327-301-5 PMID 19554288
- ^ Conrath, K E; Wernery, U; Muyldermans, S; Nguyen, V K 2003 "Emergence and evolution of functional heavy-chain antibodies in Camelidae" Developmental and Comparative Immunology 27 2: 87–103 doi:101016/S0145-305X0200071-X PMID 12543123
- ^ "Nanobodies" Nanobodyorg 2006
- ^ Ghannam, A, Kumari, S, Muyldermans, S, & Abbady, A Q 2015 Camelid nanobodies with high affinity for broad bean mottle virus: a possible promising tool to immunomodulate plant resistance against viruses Plant Molecular Biology, 1-15
- Wikilite: Biology of immunoglobulin light chains
|see also disorders of globin and globulin proteins|
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