Electrostatic repulsion between molecules of like charge can be misinterpreted as binding.
Spectroscopic methods have shown that Ca2+ chelators interact with Ca2(+)-binding proteins. These spectral alterations have been interpreted as evidence for the binding of chelator by the proteins. We show by direct examination of EDTA interaction with calmodulin and alpha-lactalbumin that these proteins repel EDTA rather than bind it. The repulsion is reduced by increased salt concentration but is unaffected by Ca2+ binding to the proteins. The acidic protein, alpha-lactalbumin, repells the negatively charged EDTA and inorganic phosphate whereas the basic protein, lysozyme, repells the positively charged spermine. Thus, spectroscopic changes induced by negatively charged Ca2+ chelators on negatively charged Ca2(+)-binding proteins are due to electrostatic repulsion, and not to binding. These observations underscore the possible pitfalls of using spectroscopic methods alone to analyze protein-ligand interactions.
Stemmer
P
P
Laboratory of Biochemistry, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.
Klee
C B
CB
D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism; D004492:Edetic Acid / Q000378:metabolism*; D004563:Electrochemistry; D007700:Kinetics; D007768:Lactalbumin / Q000378:metabolism; D009113:Muramidase / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism; D011485:Protein Binding; D013096:Spermine / Q000378:metabolism
D002135:Calcium-Binding Proteins; D002147:Calmodulin; D010710:Phosphates; D013096:Spermine; D007768:Lactalbumin; D004492:Edetic Acid; D009113:Muramidase; D002118:Calcium