title: High affinity agonistic metal ion binding sites within the melanocortin 4 receptor illustrate conformational change of transmembrane region 3.
abstract: We created a molecular model of the human melanocortin 4 receptor (MC4R) and introduced a series of His residues into the receptor protein to form metal ion binding sites. We were able to insert micromolar affinity binding sites for zinc between transmembrane region (TM) 2 and TM3 where the metal ion alone was able to activate this peptide binding G-protein-coupled receptor. The exact conformation of the metal ion interactions allowed us to predict the orientation of the helices, and remodeling of the receptor protein indicated that Glu100 and Ile104 in TM2 and Asp122 and Ile125 in TM3 are directed toward a putative area of activation of the receptor. The molecular model suggests that a rotation of TM3 may be important for activation of the MC4R. Previous models of G-protein-coupled receptors have suggested that unlocking of a stabilizing interaction between the DRY motif, in the cytosolic part of TM3, and TM6 is important for the activation process. We suggest that this unlocking process may be facilitated through creation of a new interaction between TM3 and TM2 in the MC4R.
authors.affiliation: Department of Neuroscience, Uppsala University, BMC, Box 593, 751 24, Uppsala, Sweden.
authors.forename: Malin C
authors.initials: MC
authors.lastname: Lagerström
authors.forename: Janis
authors.initials: J
authors.lastname: Klovins
authors.forename: Robert
authors.initials: R
authors.lastname: Fredriksson
authors.forename: Davids
authors.initials: D
authors.lastname: Fridmanis
authors.forename: Tatjana
authors.initials: T
authors.lastname: Haitina
authors.forename: Maria K
authors.initials: MK
authors.lastname: Ling
authors.forename: Magnus M
authors.initials: MM
authors.lastname: Berglund
authors.forename: Helgi B
authors.initials: HB
authors.lastname: Schiöth
mesh_terms: D020816:Amino Acid Motifs; D001665:Binding Sites; D002460:Cell Line; D000242:Cyclic AMP / Q000096:biosynthesis; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry; D017354:Point Mutation; D011485:Protein Binding; D011487:Protein Conformation; D044105:Receptor, Melanocortin, Type 4 / Q000819:agonists / Q000737:chemistry* / Q000235:genetics; D043562:Receptors, G-Protein-Coupled / Q000737:chemistry; D014162:Transfection; D015032:Zinc / Q000737:chemistry*
chemical_list: C470072:MC4R protein, human; D008565:Membrane Proteins; D044105:Receptor, Melanocortin, Type 4; D043562:Receptors, G-Protein-Coupled; D000242:Cyclic AMP; D015032:Zinc