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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

The omalizumab-Fv region.(a) Electrostatic potentials derived from the 2.42 Å crystal structure; arrows indicate the residues implicated in binding IgE from site-directed mutagenesis studies. (b) Packing and hydrogen-bonding interactions of the three histidines in the H3 loop. (c) Interactions of L1:Asp30 showing that its side chain points away from the protein surface. Omalizumab-Fv residues are in green and IgE residues in blue.
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f3: The omalizumab-Fv region.(a) Electrostatic potentials derived from the 2.42 Å crystal structure; arrows indicate the residues implicated in binding IgE from site-directed mutagenesis studies. (b) Packing and hydrogen-bonding interactions of the three histidines in the H3 loop. (c) Interactions of L1:Asp30 showing that its side chain points away from the protein surface. Omalizumab-Fv residues are in green and IgE residues in blue.

Mentions: The 2.42-Å crystal structure of the omalizumab-Fab region shows a highly negatively charged surface (see Fig. 3a, which shows the surface electrostatic potentials from the APBS program25 for the six CDRs). The L1, L2, and L3 CDRs exhibit negative surface potentials, whereas the heavy chain CDR loops are neutral. Surprisingly, the three histidines in the H3 loop (His97, His100a, and His100c), which were assumed to be positively charged in previous works1426, are predicted to be neutral by five programs (Reduce27, Whatif28, PDB2PR29, PROPKA330, and HAAD31). The neutral state of H3:His100c is consistent with its low solvent-accessible surface area (SASA) of 3% in the crystal structure. Although H3:His100a (SASA = 15%) and H3:His97 (SASA = 31%) are partially solvent exposed, they are hydrogen-bonded to each other and well-packed with vdW contacts to nearby hydrophobic residues including H3:His100c (Fig. 3b). The H3, L1, and L3 loops contain residues implicated in direct/indirect binding to IgE from site-directed mutagenesis studies26, namely, H3:His97, H3:His100c, L1:Asp30, L3:Glu93, and L3:Asp94.


Structural and Physical Basis for Anti-IgE Therapy.

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

The omalizumab-Fv region.(a) Electrostatic potentials derived from the 2.42 Å crystal structure; arrows indicate the residues implicated in binding IgE from site-directed mutagenesis studies. (b) Packing and hydrogen-bonding interactions of the three histidines in the H3 loop. (c) Interactions of L1:Asp30 showing that its side chain points away from the protein surface. Omalizumab-Fv residues are in green and IgE residues in blue.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: The omalizumab-Fv region.(a) Electrostatic potentials derived from the 2.42 Å crystal structure; arrows indicate the residues implicated in binding IgE from site-directed mutagenesis studies. (b) Packing and hydrogen-bonding interactions of the three histidines in the H3 loop. (c) Interactions of L1:Asp30 showing that its side chain points away from the protein surface. Omalizumab-Fv residues are in green and IgE residues in blue.
Mentions: The 2.42-Å crystal structure of the omalizumab-Fab region shows a highly negatively charged surface (see Fig. 3a, which shows the surface electrostatic potentials from the APBS program25 for the six CDRs). The L1, L2, and L3 CDRs exhibit negative surface potentials, whereas the heavy chain CDR loops are neutral. Surprisingly, the three histidines in the H3 loop (His97, His100a, and His100c), which were assumed to be positively charged in previous works1426, are predicted to be neutral by five programs (Reduce27, Whatif28, PDB2PR29, PROPKA330, and HAAD31). The neutral state of H3:His100c is consistent with its low solvent-accessible surface area (SASA) of 3% in the crystal structure. Although H3:His100a (SASA = 15%) and H3:His97 (SASA = 31%) are partially solvent exposed, they are hydrogen-bonded to each other and well-packed with vdW contacts to nearby hydrophobic residues including H3:His100c (Fig. 3b). The H3, L1, and L3 loops contain residues implicated in direct/indirect binding to IgE from site-directed mutagenesis studies26, namely, H3:His97, H3:His100c, L1:Asp30, L3:Glu93, and L3:Asp94.

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