FIGURE 1.

Scheme highlighting the M3R sequences that were subjected to Cys substitution mutagenesis. Single Cys substitutions were introduced into a modified version of the rat M3R that lacked most endogenous Cys residues (M3′(3C)-Xa; see ”Experimental Procedures“ for details). Endogenous Cys residues were replaced with either serine or alanine (open squares), except for Cys¹⁴⁰, Cys²²⁰, and Cys⁵³² (19). Solid circles indicate amino acids that were subjected to Cys substitution mutagenesis (Arg¹⁷⁶–Thr¹⁸⁰ and Lys⁵⁴⁸–Thr⁵⁵⁶).