Multiple sequence alignment of class A GPCRs. For easy visualization the logo of the MSA alignment is generated using Weblogo (http://weblogo.berkeley.edu). The amino acids numbering is based on the positions of bovine opsin (NCBI Reference Sequence: NP_001014890.1). The individual letter height of amino acid(s) at each position indicates their relative frequencies and conservation in the alignment. The TM helices are indicated as lines above the sequence. Most of the conserved regions are restricted to TM regions.