Approximate calculation and experimental derivation of native isoelectric points of membrane protein complexes of Arabidopsis chloroplasts and mitochondria

Electric charges are important intrinsic properties of proteins. They directly affect functionality and also mediate interactions with other molecules such as cofactors, substrates and regulators of enzymatic activity, with lipids as well as other proteins. As such, analysis of the electric properties of proteins gives rise to improved understanding of the mechanism by which proteins fulfil their specific functions. This is not only true for singular proteins but also applies for defined assemblies of proteins, protein complexes and supercomplexes. Charges in proteins often are a consequence of the presence of basic and acidic amino acid residues within polypeptide chains. In liquid phase, charge distributions of proteins change in response to the pH of their environment. The interdependence of protein charge and the surrounding pH is best described by the isoelectric point, which is notoriously difficult to obtain for native protein complexes. Here, experimentally derived native isoelectric points (npls) for a range mitochondrial and plastid protein complexes are provided. In addition, for four complexes, npls were calculated by a novel approach which yields results largely matching the experimental npls. (C) 2012 Elsevier B.V. All rights reserved.