pH Dependence of Charge Multipole Moments in Proteins

• Published in: Biophysical journal Vol. 113; no. 7; pp. 1454 - 1465
• Main Authors: Lošdorfer Božič, Anže, Podgornik, Rudolf
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 03.10.2017; Biophysical Society; The Biophysical Society
• Subjects: Acidity; Amino acids; Amino Acids - chemistry; Amino Acids - metabolism; Animals; Biophysics; Capsid Proteins - chemistry; Capsid Proteins - metabolism; Cattle; Charge distribution; Chickens; Colloids; Dipole moments; Egg Proteins - chemistry; Egg Proteins - metabolism; Electrostatic properties; Electrostatics; Humans; Hydrogen ions; Hydrogen-Ion Concentration; Lactoglobulins - chemistry; Lactoglobulins - metabolism; Levivirus; Models, Molecular; Multipoles; Muramidase - chemistry; Muramidase - metabolism; pH effects; Protein interaction; Protein Structure, Tertiary; Proteins; Quadrupoles; Serum Albumin - chemistry; Serum Albumin - metabolism; Shells; Solvents - chemistry; Spatial distribution; Static Electricity; Structure-function relationships; Surface charge; Surface Properties
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/j.bpj.2017.08.017

Electrostatic interactions play a fundamental role in the structure and function of proteins. Due to ionizable amino acid residues present on the solvent-exposed surfaces of proteins, the protein charge is not constant but varies with the changes in the environment—most notably, the pH of the surrounding solution. We study the effects of pH on the charge of four globular proteins by expanding their surface charge distributions in terms of multipoles. The detailed representation of the charges on the proteins is in this way replaced by the magnitudes and orientations of the multipole moments of varying order. Focusing on the three lowest-order multipoles—the total charge, dipole, and quadrupole moment—we show that the value of pH influences not only their magnitudes, but more notably and importantly also the spatial orientation of their principal axes. Our findings imply important consequences for the study of protein-protein interactions and the assembly of both proteinaceous shells and patchy colloids with dissociable charge groups.