Determination of the pKa values of titratable groups of an antigen-antibody complex, HyHEL-5-hen egg lysozyme |
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| Authors: | McDonald Shawn M; Willson Richard C; McCammon JAndrew |
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| Affiliation: | 1Departments of Chemistry, University of Houston Houston, TX 77204, USA
2Departments of Chemical Engineering, University of Houston Houston, TX 77204, USA
3Present address: Department of Chemistry and Biochemistry and Department of Pharmacology, University of California at San Diego La Jolla, CA 92093-0365, USA |
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| Abstract: | The titration behavior of the ionizable residues of the HyHEL-5–henegg lysozyme complex and its individual components has beenstudied using continuum electrostatic calculations. Severalresidues of HyHEL-5 had pKa values shifted away from model valuesfor isolated residues by more than three pH units. Shifts awayfrom the model values were smaller for the residues of hen egglysozyme. A moderate variation in the pKa values of the titratablegroups was observed upon increase of the ionic strength from0 to 100 mM, amounting to 1–2 pH units in most cases.Under physiological conditions, the net charge of HyHEL-5 wasopposite that for hen egg lysozyme. Several residues, includingthose involved in the Arg–Glu salt bridges that have beenproposed to be important in antibody-antigen binding, had pKavalues that were changed significantly upon binding. The maintitration event upon antibody-antigen binding appears to beloss of a proton from residue GluH50 of the Fv molecule. Thelimitations of our calculation methods and the role they mightplay in the design of antibodies for use in assays, sensorsand separations are discussed |
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| Keywords: | antibody/ electrostatics/ protonation state/ titration |
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