sentence: Through analyzing contacts between side chains in all possible X-ray structures of class A GPCRs , they noticed that in all inactive structures the 3x46 residue ( ‘ x ’ instead of dot indicates the GPCRdb numbering scheme [ 34 ] used by the authors in the original report , largely analogical to the Ballesteros-Weinstein scheme ) interacts with the 6x37 side chain , while in all active structures it prefers contact with the 7x53 residue from the NPxxY conserved motif .