Figure 6: Electrostatic interactions between the receptor molecule and the HAMP domain.
From: New Insights on Signal Propagation by Sensory Rhodopsin II/Transducer Complex

Interacting patches in the receptor and the transducer are shown and the G-D-G-D-L-D patch of the transducer proposed previously in literature as interacting with NpSRII. Positive charges are mapped in blue and negative are mapped in red. The expected salt bridges are: Asp214 (NpSRII) to Lys21 (NpHtrII), Lys157 (NpSRII) to Asp119 and Glu116 (NpHtrII).