Scheme 3: Extracellular domain of PTH1R has a high density of negatively charged residues.

Snake plot of PTH1R shows negatively charged residues in red, which are clustered towards the extracellular side of the receptor. Two regions of PTH1R not conserved in family B GPCRs are boxed: the 50-residue flexible loop contains 8 negatively charged residues and the 16-residue extracellular loop 1 contains 6 negatively charged residues.