title: The solution structure of melanoma growth stimulating activity.
abstract: The solution structure of melanoma growth stimulating activity (MGSA), a dimeric chemokine consisting of 73 residues per monomer, has been determined using two-dimensional homonuclear and three-dimensional heteronuclear NMR spectroscopy. Structure calculations were carried out using a hybrid distance geometry-simulated annealing approach with the programs DGII and X-PLOR. The structure is based on a total of 2362 experimental restraints, comprising 2150 NOE-derived distance restraints (2076 unambiguous intrasubunit restraints, 60 unambiguous intersubunit restraints, and 14 ambiguous restraints with potential contributions from both intra- and intersubunit NOEs), 84 distance restraints for 42 backbone hydrogen bonds, and 128 torsion angle restraints. The ambiguous distance restraints were treated using a target function which accounts for both intra- and intermolecular contributions to the NOE intensity. A total of 25 structures were calculated, with the backbone (N, C alpha, C) atomic r.m.s. distribution about the mean coordinates for residues 8 to 69 being 0.44(+/- 0.10) A for the dimer and 0.34(+/- 0.07) A for the individual monomers. The N- and C-terminal residues (1 to 7 and 70 to 73, respectively) are disordered. The overall structure of the MGSA dimer is similar to that reported previously for the NMR and X-ray structures of interleukin-8 (IL-8), and consists of a six-stranded antiparallel beta-sheet packed against two C-terminal antiparallel alpha-helices. A best fit superposition of the NMR structure of MGSA on the X-ray and NMR structures of IL-8 yields backbone atomic r.m.s. differences of 0.99 and 1.28 A, respectively for individual monomers, and 1.08 and 1.82 A, respectively for the dimers (using MGSA residues 8 to 14 and 19 to 69). In general, the MGSA structure resembles the IL-8 X-ray structure more than it does the IL-8 NMR structure. At the tertiary (monomer) level the two main differences between the MGSA solution structure and IL-8 NMR structure involve the loops between residues 14 to 19 and between residues 30 to 38. At the quaternary (dimer) level the difference results from differing angles between the beta-strands which form the dimer interface, and is manifest as a different interhelical separation (distance of closest approach between the two helices is 15.3 A in the IL-8 NMR structure and 11.7 (+/- 0.4) A in the MGSA structure).
authors.affiliation: Department of Protein Engineering, Genentech, Inc., South San Francisco, CA 94080-4990.
authors.forename: W J
authors.initials: WJ
authors.lastname: Fairbrother
authors.forename: D
authors.initials: D
authors.lastname: Reilly
authors.forename: T J
authors.initials: TJ
authors.lastname: Colby
authors.forename: J
authors.initials: J
authors.lastname: Hesselgesser
authors.forename: R
authors.initials: R
authors.lastname: Horuk
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D054360:Chemokine CXCL1; D019743:Chemokines, CXC; D002630:Chemotactic Factors / Q000737:chemistry* / Q000235:genetics; D006133:Growth Substances / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D006860:Hydrogen Bonding; D036341:Intercellular Signaling Peptides and Proteins; D016209:Interleukin-8 / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D015394:Molecular Structure; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry
chemical_list: D000596:Amino Acids; C475829:CXCL1 protein, human; D054360:Chemokine CXCL1; D019743:Chemokines, CXC; D002630:Chemotactic Factors; D006133:Growth Substances; D036341:Intercellular Signaling Peptides and Proteins; D016209:Interleukin-8; D011994:Recombinant Proteins