Three-Dimensional Structure of ProteinsRotation around the a-Carbon in a PolypeptideA Sterically Nonallowed ConformationThe -Helix and -Pleated SheetPowerPoint PresentationSlide 6Slide 7Antiparallel and Parallel  Pleated SheetsSlide 9Slide 10Other Possible Secondary StructuresHydrogen Bonding Patterns for Different HelicesRamachandran PlotFibrous Proteins Proteins with an elongated or filamentous form, often dominated by a single type of secondary structure over a large distance.Structure of Keratin and Keratin-Type Intermediate FilamentsSlide 16Coiled-Coil -Helical Dimer of a KeratinSlide 18Structure of Silk FibroinSlide 20Structure of Collagen FibersSlide 22Slide 23The Collagen Triple Helix (Tropocollagen)Post-Translational Modifications in CollagenThree-Dimensional Structure of ProteinsRotation around the -Carbon in a PolypeptideA Sterically Nonallowed ConformationThe -Helix and -Pleated Sheet-Helix:•3.6 residues/turn•Rise = 0.15 nm/residue•13-atom hydrogen-bonded loop-Pleated Sheet:•anti-parallel or parallel•2.0 residues/”turn”•0.34 nm/residue (anti-parallel) or 0.32 nm/residue (parallel)QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Conformationally and allowable structures where backbone is optimally hydrogen-bonded (linear H-bonds)Linus Pauling and Robert Corey, 1950Linus Pauling and Robert Corey, 1951Helices have electric dipoles.Antiparallel and Parallel  Pleated SheetsOther Possible Secondary Structures310 Helix:•3 residues/turn•0.20 nm/residue•10-atom hydrogen-bonded loop Helix:•4.4 residues/turn•0.12 nm/residue•16-atom hydrogen-bonded loopQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Hydrogen Bonding Patterns for Different HelicesRamachandran PlotG.N. Ramachandran, 1963QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Fibrous ProteinsProteins with an elongated or filamentous form, often dominated by a single type of secondary structure over a large distance.Most fibrous proteins are associated with connective tissue and help provide mechanical strength to the tissue.Structure of Keratin and Keratin-Type Intermediate FilamentsAdjacent polypeptide chains also crosslinked by disulfide bonds.Disulfide bond patterns between are what determine whether human hair is straight or curly.Keratin is a principal component of hair, horn, nails and feathers.Coiled-Coil -Helical Dimer of  KeratinAmphipathic  helices: Residues a, d, a’ and d’ hydrophobic, other residues more hydrophilicStructure of Silk FibroinSilk made by silkworms and spiders.Composed of microcrystalline array of antiparallel pleated sheets where each strand has alternating Gly and Ala or Ser residues.Structure of Collagen Fibers•3 intertwined left-handed helices•3.3 residues/turn•Repeating Gly-X-Y (X often Pro, Y often Pro or hydroxyPro)Collagen is the most abundant vertebrate protein and the major stress-bearing component of connective tissue (bone, teeth, cartilage, tendon) and fibrous matrix of skin and blood vessels.The Collagen Triple Helix (Tropocollagen)Tropocollagen with Gly Ala substitution (yellow)Interactions between strandsG.N. Ramachandran, 1955Post-Translational Modifications in CollagenQuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Collagen contains unusual oxidized and crosslinked lysine residues.Lysyl oxidase is the enzyme that oxidizes lysine residues to the aldehyde allysine, which then forms the crosslinks.QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.Hydroxyproline is also found in collagen. (Some lysine residues also hydroxylated.) The enzyme required for hydroxylation of proline residues is prolyl hydroxylase, a vitamin C-dependent enzyme.Scurvy is caused by reduced hydroxyproline in collagen as a result of vitamin C