Abstract
Simple SummaryLike many other molecules playing vital functions in animals, the antibody molecule possesses a complex structure with distinctive features. The structure of the basic unit, i.e., the immunoglobulin domain of very ancient origin is substantially simple. However, high complexity resides in the types and numbers of the domains composing the whole molecule. The emergence of the antibody molecule during evolution overturned the effectiveness of the organisms’ defense system. The particular organization of the coding genes, the mechanisms generating antibody diversity, and the plasticity of the overall protein structure, attest to an extraordinary successful evolutionary history. Here, we attempt to trace, across the evolutionary scale, the very early origins of the most significant features characterizing the structure of the antibody molecule and of the molecular mechanisms underlying its major role in recognizing an almost unlimited number of pathogens.The vertebrate immune system provides a powerful defense because of the ability to potentially recognize an unlimited number of pathogens. The antibody molecule, also termed immunoglobulin (Ig) is one of the major mediators of the immune response. It is built up from two types of Ig domains: the variable domain, which provides the capability to recognize and bind a potentially infinite range of foreign substances, and the constant domains, which exert the effector functions. In the last 20 years, advances in our understanding of the molecular mechanisms and structural features of antibody in mammals and in a variety of other organisms have uncovered the underlying principles and complexity of this fundamental molecule. One notable evolutionary topic is the origin and evolution of antibody. Many aspects have been clearly stated, but some others remain limited or obscure. By considering a wide range of prokaryotic and eukaryotic organisms through a literature survey about the topic, we have provided an integrated view of the emergence of antibodies in evolution and underlined the very ancient origins.
Highlights
Receptors that are capable of recognizing non-self molecular structures are found in a diverse array of multicellular organisms
A fundamental role in the evolution of the antibody architecture is played by the so-called hinge region—the key region that accounts for the functionality of the antibody, which is located in the middle of the molecule
Phyla of the key elements related to the evolution
Summary
Receptors that are capable of recognizing non-self molecular structures are found in a diverse array of multicellular organisms. V (variable), D (diversity), J (joining) gene segments, which contribute to encoding the IgV domain through a mechanism of “somatic recombination.”. The IgV domain possesses a distinctive feature, that is a region, encoded by a J gene segment, which forms a diglycine bulge and is important for the V domain dimerization. These types of V domains are known as VJ sets or VJ V domains [3]. A key role in the folding dynamics is played by the clustering of the hydrophobic residues in strands B, C, E, and F They are required for priming the folding nucleus of the Ig domain and for the formation of the disulfide bridge between strands B and F. We look through species that preceded the jawed vertebrates in an attempt to reconstruct the structural and functional properties that have resulted to be essential for the antibody assembly and to describe the most important steps that have led to its diversification in jawed vertebrates
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