title: Crystal structures of a nonapeptide helix containing alpha, alpha-di-n-butylglycine (Dbg), Boc-Gly-Dbg-Ala-Val-Ala-Leu-Aib-Val-Leu-OMe.
abstract: Two crystal structures of a nonapeptide (anhydrous and hydrated) containing the amino acid residue alpha, alpha-di-n-butylglycyl, reveal a mixed 3(10)-/alpha-helical conformation. Residues 1-7 adopt phi, psi values in the helical region, with Val(8) being appreciably distorted. The Dbg residue has phi, psi values of -40, -37 degrees and -46, -40 degrees in the two crystals with the two butyl side chains mostly extended in each. Peptide molecules in the crystals pack into helical columns. The crystal parameters are: C50H91N9O12, space group P2(1), with a = 9.789(1) A, b = 20.240(2) A, c = 15.998(3) A, beta = 103.27(1); Z = 2, R = 10.3% for 1945 data observed > 3 sigma (F) and C50H91N9O12.3H2O, space group P2(1), with a = 9.747(3) A, b = 21.002(8) A, c = 15.885(6) A, beta = 102.22(3) degrees, Z = 2, R = 13.6% for 2535 data observed > 3 sigma (F). The observation of a helical conformation at Dbg suggests that the higher homologs in the alpha, alpha-dialkylated glycine series also have a tendency to stabilize peptide helices.
authors.affiliation: Laboratory for the Structure of Matter, Naval Research Laboratory, Washington, DC, USA.
authors.forename: I L
authors.initials: IL
authors.lastname: Karle
authors.forename: R
authors.initials: R
authors.lastname: Gurunath
authors.forename: S
authors.initials: S
authors.lastname: Prasad
authors.forename: R B
authors.initials: RB
authors.lastname: Rao
authors.forename: P
authors.initials: P
authors.lastname: Balaram
mesh_terms: D009646:Norleucine / Q000031:analogs & derivatives* / Q000737:chemistry; D011487:Protein Conformation; D017510:Protein Folding; D014961:X-Ray Diffraction
chemical_list: C092836:alpha,alpha-di-n-butylglycine; D009646:Norleucine