University of Illinois at Urbana-Champaign, Urbana IL, USA
The pH-dependent behavior and protonation state of individual residues in proteins, which are very important for protein function, are often difficult to determine experimentally. Continuum electrostatic methods have been used to model the titrations of individual amino acid residues in their protein environments. Macroscopic properties of two large protein systems have been successfully reproduced. We examine complexes of two monoclonal antibodies raised against hen egg lysozyme with hen egg and bobwhite quail lysozyme. Electrostatics can help in understanding the very different affinity constants of homologous, and nearly structurally identical antibodies for these proteins. Another system where pH dependent behavior plays a key role in function is the photosynthetic reaction center. We calculate the titration behavior of key residues involved in the electron transfer and redox process in the reaction center. Two amino acid residues which have been determined experimentally to be critical for proton uptake are calculated to gain 1.4 protons in the course of the reaction center's quinone reduction cycle. The pH dependence of proton uptake is successfully reproduced.