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Structural and Physical Basis for Anti-IgE Therapy.

Wright JD, Chu HM, Huang CH, Ma C, Chang TW, Lim C - Sci Rep (2015)

Bottom Line: Mutagenesis studies indicate overlapping FcεRI and omalizumab-binding sites in the Cε3 domain, but crystallographic studies show FcεRI and CD23-binding sites that are far apart, so how can omalizumab block IgE from binding both receptors?These results provide a structural and physical basis as to why omalizumab cannot bind receptor-bound IgE and why omalizumab-bound IgE cannot bind to CD23/FcεRI.They reveal the key IgE residues and their roles in binding omalizumab, CD23, and FcεRI.

View Article: PubMed Central - PubMed

Affiliation: 1] Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan [2] The Genomics Research Center, Academia Sinica 115, Taiwan.

ABSTRACT
Omalizumab, an anti-IgE antibody, used to treat severe allergic asthma and chronic idiopathic urticaria, binds to IgE in blood or membrane-bound on B lymphocytes but not to IgE bound to its high (FcεRI) or low (CD23) affinity receptor. Mutagenesis studies indicate overlapping FcεRI and omalizumab-binding sites in the Cε3 domain, but crystallographic studies show FcεRI and CD23-binding sites that are far apart, so how can omalizumab block IgE from binding both receptors? We report a 2.42-Å omalizumab-Fab structure, a docked IgE-Fc/omalizumab-Fab structure consistent with available experimental data, and the free energy contributions of IgE residues to binding omalizumab, CD23, and FcεRI. These results provide a structural and physical basis as to why omalizumab cannot bind receptor-bound IgE and why omalizumab-bound IgE cannot bind to CD23/FcεRI. They reveal the key IgE residues and their roles in binding omalizumab, CD23, and FcεRI.

No MeSH data available.


Related in: MedlinePlus

Conformational changes in the IgE-Fc upon binding its receptors.Top: The Cε3 domains adopt a closed conformation when bound to CD23 (PDB 4gko), an open one when bound to FcεRI (PDB 1f6a), and a hybrid conformation with chain A “open” and chain B “closed” when IgE is free in solution (PDB 2wqr). Bottom: The Cε2 domains adopt a bent conformation with contacts to one of the Cε3-4 domains in free IgE (PDB 2wqr), becomes even more bent upon binding FcεRI (PDB 2y2q), but is extended when bound to two non-omalizumab anti-IgE molecules (PDB 4j4p).
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f2: Conformational changes in the IgE-Fc upon binding its receptors.Top: The Cε3 domains adopt a closed conformation when bound to CD23 (PDB 4gko), an open one when bound to FcεRI (PDB 1f6a), and a hybrid conformation with chain A “open” and chain B “closed” when IgE is free in solution (PDB 2wqr). Bottom: The Cε2 domains adopt a bent conformation with contacts to one of the Cε3-4 domains in free IgE (PDB 2wqr), becomes even more bent upon binding FcεRI (PDB 2y2q), but is extended when bound to two non-omalizumab anti-IgE molecules (PDB 4j4p).

Mentions: Interestingly, the X-ray structures of IgE free and bound to its receptors or anti-IgE show different conformations (orientations) for the Cε2 and Cε3 domains relative to the Cε3 and Cε4 domains, respectively. Relative to the Cε4 domains, the Cε3 domains are “closed” when bound to the CD23 but are “open” when bound to FcεRI (Fig. 2, top). The closed Cε3-Cε4 conformation seen bound to CD23 cannot bind to FcεRI17, but can bind to omalizumab21, whereas the open Cε3-Cε4 conformation seen bound to FcεRI cannot bind to CD2317. In contrast to the receptor-bound IgE structures, the free IgE structure (PDB 2wqr) shows an open Cε3-Cε4 conformation in one chain and a closed one in the other, while the Cε2 domain pair folds back against the Cε3 domains (Fig. 2, bottom). This bend of the Cε2 domain relative to Cε3 is apparently unaffected by binding to CD2322, but is enhanced by binding to FcεRI16, and becomes unbent upon binding to an anti-IgE antibody20 (Fig. 2, bottom).


Structural and Physical Basis for Anti-IgE Therapy.

Wright JD, Chu HM, Huang CH, Ma C, Chang TW, Lim C - Sci Rep (2015)

Conformational changes in the IgE-Fc upon binding its receptors.Top: The Cε3 domains adopt a closed conformation when bound to CD23 (PDB 4gko), an open one when bound to FcεRI (PDB 1f6a), and a hybrid conformation with chain A “open” and chain B “closed” when IgE is free in solution (PDB 2wqr). Bottom: The Cε2 domains adopt a bent conformation with contacts to one of the Cε3-4 domains in free IgE (PDB 2wqr), becomes even more bent upon binding FcεRI (PDB 2y2q), but is extended when bound to two non-omalizumab anti-IgE molecules (PDB 4j4p).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4481376&req=5

f2: Conformational changes in the IgE-Fc upon binding its receptors.Top: The Cε3 domains adopt a closed conformation when bound to CD23 (PDB 4gko), an open one when bound to FcεRI (PDB 1f6a), and a hybrid conformation with chain A “open” and chain B “closed” when IgE is free in solution (PDB 2wqr). Bottom: The Cε2 domains adopt a bent conformation with contacts to one of the Cε3-4 domains in free IgE (PDB 2wqr), becomes even more bent upon binding FcεRI (PDB 2y2q), but is extended when bound to two non-omalizumab anti-IgE molecules (PDB 4j4p).
Mentions: Interestingly, the X-ray structures of IgE free and bound to its receptors or anti-IgE show different conformations (orientations) for the Cε2 and Cε3 domains relative to the Cε3 and Cε4 domains, respectively. Relative to the Cε4 domains, the Cε3 domains are “closed” when bound to the CD23 but are “open” when bound to FcεRI (Fig. 2, top). The closed Cε3-Cε4 conformation seen bound to CD23 cannot bind to FcεRI17, but can bind to omalizumab21, whereas the open Cε3-Cε4 conformation seen bound to FcεRI cannot bind to CD2317. In contrast to the receptor-bound IgE structures, the free IgE structure (PDB 2wqr) shows an open Cε3-Cε4 conformation in one chain and a closed one in the other, while the Cε2 domain pair folds back against the Cε3 domains (Fig. 2, bottom). This bend of the Cε2 domain relative to Cε3 is apparently unaffected by binding to CD2322, but is enhanced by binding to FcεRI16, and becomes unbent upon binding to an anti-IgE antibody20 (Fig. 2, bottom).

Bottom Line: Mutagenesis studies indicate overlapping FcεRI and omalizumab-binding sites in the Cε3 domain, but crystallographic studies show FcεRI and CD23-binding sites that are far apart, so how can omalizumab block IgE from binding both receptors?These results provide a structural and physical basis as to why omalizumab cannot bind receptor-bound IgE and why omalizumab-bound IgE cannot bind to CD23/FcεRI.They reveal the key IgE residues and their roles in binding omalizumab, CD23, and FcεRI.

View Article: PubMed Central - PubMed

Affiliation: 1] Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan [2] The Genomics Research Center, Academia Sinica 115, Taiwan.

ABSTRACT
Omalizumab, an anti-IgE antibody, used to treat severe allergic asthma and chronic idiopathic urticaria, binds to IgE in blood or membrane-bound on B lymphocytes but not to IgE bound to its high (FcεRI) or low (CD23) affinity receptor. Mutagenesis studies indicate overlapping FcεRI and omalizumab-binding sites in the Cε3 domain, but crystallographic studies show FcεRI and CD23-binding sites that are far apart, so how can omalizumab block IgE from binding both receptors? We report a 2.42-Å omalizumab-Fab structure, a docked IgE-Fc/omalizumab-Fab structure consistent with available experimental data, and the free energy contributions of IgE residues to binding omalizumab, CD23, and FcεRI. These results provide a structural and physical basis as to why omalizumab cannot bind receptor-bound IgE and why omalizumab-bound IgE cannot bind to CD23/FcεRI. They reveal the key IgE residues and their roles in binding omalizumab, CD23, and FcεRI.

No MeSH data available.


Related in: MedlinePlus