Electrospray Surface Charge Describes Protein Molecular Motion
The electrospray mass/charge distribution for a protein is an instantaneous measurement of surface areas during the transition from liquid to gas phase. Protonation is dependent upon surface area and surface area is related to protein folding under all conditions. M/z distributions for proteins and protein analogues all with different degrees of entropy were compared. Rigid dipeptide self-assemblies of any size possess a single m/z, whereas protein always displays multiple m/z distributions. Native proteins have narrow, defined m/z distributions, while denatured proteins and synthetic homopolypetides possess the widest possible m/z distributions. These observations are consistent with dynamic changes in surface area resulting from molecular motion.