Fig. 6.

An overview of the emergence of A- and B-type mAChRs in Protostomia (highlighted by blue lines) and Deuterostomia (highlighted by red lines). Cnidarians evolved before the split of Proto- and Deuterostomia, which is indicated by a purple line. The B-type mAChRs appear to be confined to the Protostomia, whereas the A-type receptors occur in both evolutionary lineages and in cnidarians. Our criteria for assigning the receptors as A- or B-type were (1) comparisons of their overall protein sequences, using phylogenetic tree analyses (Fig. S13) and (2) the presence (A-type) or absence (B-type) of residues identical to the m2 QNB-specific binding residues S107, V111, W155, T187, and T190 (See Fig. 5 and “Discussion”). Both criteria should be fulfilled