Potential B cell epitopes of AQP4. The top two panels represent a side view (left image, Loop E facing viewer; right image Loop A to the left) of AQP4 with amino acid residues shown in helical, space-filling, or ball and stick format. The space-filling format represents the proposed extracellular loops (Loop A, blue, Loop C green, and Loop E orange-red). Ball and stick motif represent amino acids within the loops that are potential antibody contact residues because of O (red) or N (blue) atoms available for H-bonding or salt-bridge interactions with anti-AQP4-specific IgG1. The middle panel is the top view of AQP4 with formatting the same as described for the top two images. The bottom set of images has been restricted to show only the loops. This view clearly shows the lateral projection rather than upward along the long axis of AQP4 of side-chains of amino acids that could interact with anti-AQP4-specific antibodies (left image, Loop E facing the viewer; right image, Loop A facing viewer). The amino acids in ball and stick representation are: Loop A, S62, E63, N64; Loop C, H151, N153, T155; Loop E, N226, E228, H229.