Functional Tolerance to Cysteine Mutations in Human α7 Nicotinic Acetylcholine Receptors

The α7 nicotinic acetylcholine receptor (α7 nAChR) is involved in various intracellular signaling pathways that mediate addiction, chronic pain, and other diseases, but its intracellular domain structures remain undetermined. The presence of 17 native cysteines in α7 nAChR provides opportunities for extracting structural information through site-directed labeling of chemical probes in strategic locations, but it also creates uncertainties in channel function when those native cysteines must be mutated. Using site-directed mutagenesis and two-electrode voltage clamp electrophysiology measurements, we found that α7 nAChR's function was well tolerated for mutations of all 13 cysteines as long as two pairs of disulfide-bond cysteines remained in the extracellular domain. Furthermore, surface plasmon resonance measurements showed that the cysteine mutations did not affect α7 nAChR binding to the intracellular protein PICK1. The study suggests that a high native cysteine content does not necessarily preclude the use of single cysteine labeling for acquiring structural information on functional proteins.