Surface charge of the Usp domain within KdpD (amino acids 253–373) compared to UspC, UspF, and UspG. The tertiary structures were obtained by ESyPred3D modeling . All four proteins/protein domains consist of a bundle of four to five β-sheets (blue) surrounded by four α-helices (red). Only charged amino acids are shown. The positively charged side chains are drawn in blue, the negatively charged side chains are drawn in red.