Fig. 8.

Molecular structure of human RhCG showing key residues. A: ribbon structure model with lateral view. Twin, coplanar histidine residues, His¹⁸⁵ and His³⁴⁴, function to stabilize NH₃ transport and provide selectivity relative to other solutes, such as NH₄, and are shown in ball-and-stick representation. Acidic residues in extracellular and intracellular vestibules, function in NH₄⁺ attraction and stabilization (Glu¹⁶⁶, Asp²¹⁸, Asp²⁷⁸, and Glu³²⁹), and are shown in space-filling representation. B: cytoplasmic view of channel, demonstrating key NH₄⁺-stabilizing acidic residues (Asp²¹⁸, Asp²⁷⁸, and Glu³²⁹), coplanar histidine residues in pore channel, and representation of extracellular vestibule acidic residue (Glu¹⁶⁶). Models were generated using BallView software, version 1.3.2 using human RhCG data (3HD6).