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Structure of colicin S4. A: left, hydration of colicin S4 in the crystal arrangement. Water molecules are represented by blue balls. Note the significant difference in hydration between domains R1 and R2. Right, structure of colicin S4. B: network of hydrophobic and electrostatic interactions between domain R2 and the pore-forming domain (stereo view). C: electrostatic characterization of colicin S4. Blue, positively charged surface; red, negatively charged surface.
