1ohq
Crystal structure of HEL4, a soluble human VH antibody domain resistant to aggregation
Structural highlights
FunctionHV323_HUMAN V region of the variable domain of immunoglobulin heavy chains that participates in the antigen recognition (PubMed:24600447). Immunoglobulins, also known as antibodies, are membrane-bound or secreted glycoproteins produced by B lymphocytes. In the recognition phase of humoral immunity, the membrane-bound immunoglobulins serve as receptors which, upon binding of a specific antigen, trigger the clonal expansion and differentiation of B lymphocytes into immunoglobulins-secreting plasma cells. Secreted immunoglobulins mediate the effector phase of humoral immunity, which results in the elimination of bound antigens (PubMed:20176268, PubMed:22158414). The antigen binding site is formed by the variable domain of one heavy chain, together with that of its associated light chain. Thus, each immunoglobulin has two antigen binding sites with remarkable affinity for a particular antigen. The variable domains are assembled by a process called V-(D)-J rearrangement and can then be subjected to somatic hypermutations which, after exposure to antigen and selection, allow affinity maturation for a particular antigen (PubMed:17576170, PubMed:20176268).[1] [2] [3] [4] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThe antigen binding site of antibodies usually comprises associated heavy (V(H)) and light (V(L)) chain variable domains, but in camels and llamas, the binding site frequently comprises the heavy chain variable domain only (referred to as V(HH)). In contrast to reported human V(H) domains, V(HH) domains are well expressed from bacteria and yeast, are readily purified in soluble form and refold reversibly after heat-denaturation. These desirable properties have been attributed to highly conserved substitutions of the hydrophobic residues of V(H) domains, which normally interact with complementary V(L) domains. Here, we describe the discovery and characterisation of an isolated human V(H) domain (HEL4) with properties similar to those of V(HH) domains. HEL4 is highly soluble at concentrations of > or =3 mM, essentially monomeric and resistant to aggregation upon thermodenaturation at concentrations as high as 56 microM. However, in contrast to V(HH) domains, the hydrophobic framework residues of the V(H):V(L) interface are maintained and the only sequence changes from the corresponding human germ-line segment (V3-23/DP-47) are located in the loops comprising the complementarity determining regions (CDRs). The crystallographic structure of HEL4 reveals an unusual feature; the side-chain of a framework residue (Trp47) is flipped into a cavity formed by Gly35 of CDR1, thereby increasing the hydrophilicity of the V(H):V(L) interface. To evaluate the specific contribution of Gly35 to domain properties, Gly35 was introduced into a V(H) domain with poor solution properties. This greatly enhanced the recovery of the mutant from a gel filtration matrix, but had little effect on its ability to refold reversibly after heat denaturation. Our results confirm the importance of a hydrophilic V(H):V(L) interface for purification of isolated V(H) domains, and constitute a step towards the design of isolated human V(H) domains with practical properties for immunotherapy. Crystal structure of HEL4, a soluble, refoldable human V(H) single domain with a germ-line scaffold.,Jespers L, Schon O, James LC, Veprintsev D, Winter G J Mol Biol. 2004 Apr 2;337(4):893-903. PMID:15033359[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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