Figure 1.

Introduction of Cys substitutions into a modified version of the rat M3R (M3′(3C)-Xa). All Cys substitutions were introduced into the M3′(3C)-Xa construct that lacked most endogenous Cys residues (see Materials and Methods for details). Endogenous Cys residues were substituted with serine or alanine (open squares), except for C140, C220, and C532, which were shown to be essential for proper M3R folding and activity (22). Solid circles indicate amino acids that were replaced with Cys residues (residues 252^5.60-265^5.73).