RT Journal Article
SR Electronic
T1 Topological and Structural Plasticity of the single Ig fold and the double Ig fold present in CD19
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 2021.06.04.447059
DO 10.1101/2021.06.04.447059
A1 Philippe Youkharibache
YR 2021
UL http://biorxiv.org/content/early/2021/06/05/2021.06.04.447059.abstract
AB The Ig-fold has had a remarkable success in vertebrate evolution, with a presence in over 2% of human genes. The Ig-fold is not just the elementary structural domain of antibodies and TCRs, it is also at the heart of a staggering 30% of immunologic cell surface receptors, making it a major orchestrator of cell-cell-interactions. While BCRs, TCRs, and numerous Ig-based cell surface receptors form homo or heterodimers on the same cell surface (in cis), many of them interface as ligand-receptors (checkpoints) on interacting cells (in trans) through their Ig domains. New Ig-Ig interfaces are still being discovered between Ig-based cell surface receptors, even in well known families such as B7. What is largely ignored however is that the Ig-fold itself is pseudo-symmetric, a property that makes the Ig-domain a versatile self-associative 3D structure and may in part explain its success in evolution, especially through its ability to bind in cis or in trans in the context of cell surface receptor-ligand interactions. In this paper we review the Ig domains tertiary and quaternary pseudo symmetries, with a particular attention to the newly identified double Ig fold in the solved CD19 molecular structure to highlight the underlying fundamental folding elements of Ig domains, i.e. Ig protodomains. This pseudosymmetric property of Ig domains gives us a decoding frame of reference to understand the fold, relate all Ig-domain forms, single or double, and suggest new protein engineering avenues.Competing Interest StatementThe authors have declared no competing interest.