title: Cis→Trans Isomerization of Pro(7) in Oxytocin Regulates Zn(2+) Binding.
abstract: Ion mobility/mass spectrometry techniques are employed to investigate the binding of Zn(2+) to the nine-residue peptide hormone oxytocin (OT, Cys(1)-Tyr(2)-Ile(3)-Gln(4)-Asn(5)-Cys(6)-Pro(7)-Leu(8)-Gly(9)-NH2, having a disulfide bond between Cys(1) and Cys(6) residues). Zn(2+) binding to OT is known to increase the affinity of OT for its receptor [Pearlmutter, A. F., Soloff, M. S.: Characterization of the metal ion requirement for oxytocin-receptor interaction in rat mammary gland membranes. J. Biol. Chem. 254, 3899-3906 (1979)]. In the absence of Zn(2+), we find evidence for two primary OT conformations, which arise because the Cys(6)-Pro(7) peptide bond exists in both the trans- and cis-configurations. Upon addition of Zn(2+), we determine binding constants in water of KA = 1.43 ± 0.24 and 0.42 ± 0.12 μM(-1), for the trans- and cis-configured populations, respectively. The Zn(2+) bound form of OT, having a cross section of Ω = 235 Å(2), has Pro(7) in the trans-configuration, which agrees with a prior report [Wyttenbach, T., Liu, D., Bowers, M. T.: Interactions of the hormone oxytocin with divalent metal ions. J. Am. Chem. Soc. 130, 5993-6000 (2008)], in which it was proposed that Zn(2+) binds to the peptide ring and is further coordinated by interaction of the C-terminal, Pro(7)-Leu(8)-Gly(9)-NH2, tail. The present work shows that the cis-configuration of OT isomerizes to the trans-configuration upon binding Zn(2+). In this way, the proline residue regulates Zn(2+) binding to OT and, hence, is important in receptor binding. Graphical Abstract ᅟ.
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, IN, 47405, USA.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Fuller
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, IN, 47405, USA.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Glover
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, IN, 47405, USA.|Merck Research Laboratories, Rahway, NJ, 07065, USA.
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Pierson
authors.affiliation: Department of Chemistry, Texas A&M University, College Station, TX, 77842, USA.
authors.forename: DoYong
authors.initials: D
authors.lastname: Kim
authors.affiliation: Department of Chemistry, Texas A&M University, College Station, TX, 77842, USA.
authors.forename: David H
authors.initials: DH
authors.lastname: Russell
authors.affiliation: Department of Chemistry, Indiana University, Bloomington, IN, 47405, USA. clemmer@indiana.edu.
authors.forename: David E
authors.initials: DE
authors.lastname: Clemmer
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D008968:Molecular Conformation; D008970:Molecular Weight; D010121:Oxytocin / Q000502:physiology*; D011392:Proline; D051381:Rats; D015032:Zinc / Q000378:metabolism*
chemical_list: D010121:Oxytocin; D011392:Proline; D015032:Zinc
keywords: Cis-trans isomerization; Ion-mobility; Oxytocin