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Crystal structure of the antigen-binding fragment of a monoclonal antibody specific for the multidrug-resistance-linked ABC transporter human P-glycoprotein.

ABSTRACT: P-glycoprotein (P-gp) is a polyspecific ATP-dependent transporter linked to multidrug resistance in cancers that plays important roles in the pharmacokinetics of a large number of drugs. The drug-resistance phenotype of P-gp can be modulated by the monoclonal antibody UIC2, which specifically recognizes human P-gp in a conformation-dependent manner. Here, the purification, sequence determination and high-resolution structure of the Fab fragment of UIC2 (UIC2/Fab) are reported. Purified UIC2/Fab binds human P-gp with a 1:1 stoichiometry. Crystals of UIC2/Fab are triclinic (space group P1), with unit-cell parameters a = 40.67, b = 44.91, c = 58.09?Å, ? = 97.62, ? = 99.10, ? = 94.09°, and diffracted X-rays to 1.6?Å resolution. The structure was determined by molecular replacement and refined to 1.65?Å resolution. The asymmetric unit contains one molecule of UIC2/Fab, which exhibits a positively charged antigen-binding surface, suggesting that it might recognize an oppositely charged extracellular epitope of P-gp.

SUBMITTER: Esser L

PROVIDER: S-EPMC4973305 | biostudies-literature | 2016 Aug

REPOSITORIES: biostudies-literature

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Crystal structure of the antigen-binding fragment of a monoclonal antibody specific for the multidrug-resistance-linked ABC transporter human P-glycoprotein.

Esser Lothar L Shukla Suneet S Zhou Fei F Ambudkar Suresh V SV Xia Di D

Acta crystallographica. Section F, Structural biology communications 20160727 Pt 8

P-glycoprotein (P-gp) is a polyspecific ATP-dependent transporter linked to multidrug resistance in cancers that plays important roles in the pharmacokinetics of a large number of drugs. The drug-resistance phenotype of P-gp can be modulated by the monoclonal antibody UIC2, which specifically recognizes human P-gp in a conformation-dependent manner. Here, the purification, sequence determination and high-resolution structure of the Fab fragment of UIC2 (UIC2/Fab) are reported. Purified UIC2/Fab ...[more]

PMID: 27487928

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Project description:BackgroundMany antibody crystal structures have been solved. Structural modeling programs have been developed that utilize this information to predict 3-D structures of an antibody based upon its sequence. Because of the problem of self-reference, the accuracy and utility of these predictions can only be tested when a new structure has not yet been deposited in the Protein Data Bank.MethodsWe have solved the crystal structure of the Fab fragment of RAC18, a protective anti-ricin mAb, to 1.9 Å resolution. We have also modeled the Fv structure of RAC18 using publicly available Ab modeling tools Prediction of Immunoglobulin Structures (PIGS), RosettaAntibody, and Web Antibody Modeling (WAM). The model structures underwent energy minimization. We compared results to the crystal structure on the basis of root-mean-square deviation (RMSD), template modeling score (TM-score), Z-score, and MolProbity analysis.FindingsThe crystal structure showed a pocket formed mainly by AA residues in each of the heavy chain complementarity determining regions (CDRs). There were differences between the crystal structure and structures predicted by the modeling tools, particularly in the CDRs. There were also differences among the predicted models, although the differences were small and within experimental error. No one modeling program was clearly superior to the others. In some cases, choosing structures based only on sequence homology to the crystallized Ab yielded RMSDs comparable to the models.ConclusionsMolecular modeling programs accurately predict the structure of most regions of antibody variable domains of RAC18. The hypervariable CDRs proved most difficult to model, particularly H chain CDR3. Because CDR3 is most often involved in contact with antigen, this defect must be considered when using models to identify potential contacts between antibody and antigen. Because this study represents only a single case, the results cannot be generalized. Rather they highlight the utility and limitations of modeling programs.

Dataset Information

Crystal structure of the antigen-binding fragment of a monoclonal antibody specific for the multidrug-resistance-linked ABC transporter human P-glycoprotein.

Publications

Crystal structure of the antigen-binding fragment of a monoclonal antibody specific for the multidrug-resistance-linked ABC transporter human P-glycoprotein.

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