Fibrous Proteins 1o structure amino acid sequence 2o structure - helix -sheet H-bonding between C=O- and N-H+ of backbone some proteins only have 1o and 2o structure: fibroin (silk) keratin hair collagen skin -sheet - helix insoluble in H2O non-polar residues Tertiary structure Primary structure sequence of amino acids Ala-Phe-Ser-Ser-Val-Glu-His-Ile-Met-Arg-Asp-Val-His-Asn-Gly Ala-Phe-Ser-Ser-Val- Glu-His-Ile-Met-Arg-Asp-Val-His-Asn-Gly- Non-polar Polar Acidic or Basic Alanine Phenylalanine Valine Isoleusine Methionine Glycine Serine Histidine Glutamic acid Arginine Aspartic acid Asperagine Tertiary structure Ala-Phe-Ser-Ser-Val-Glu-His-Ile-Met-Arg-Asp-Val-His-Asn-Gly arrange these in an -helix polar exterior 7 His 3 Ser 11 4 Asp Ser 15 Gly 8 Ile 14 Asn Val 12 10 Arg Ala 1 Glu 6 Phe His Met 2 9 13 Val 5 non-polar interior Tertiary structure interaction of the R-groups + - - - + + - hydrophobic residues inside globular proteins proteins fold around non-polar groups polar and charged residues outside Tertiary structure interactions of R-groups 1. Hydrophobic interactions non-polar R-groups LDF 2. Hydrogen bonding polar R-groups between H-bond donors and acceptors 3. Ionic bonds (salt bridges) acidic and basic R-groups ion-ion 4. Covalent bonds (disulfide) cysteins C-terminus His NH+ -O-CH Asp O Ala CH3 His Fe2+ = Arg Phe Cys S S Cys N-terminus Pro Pro Quaternary Structure hemoglobin subunits heme groups 4 - Fe globin chains 2 -chains 2 - chains held in position by interaction of R-groups H H3N + C polar histidine inside - holds Fe2+ O C O - NH N pKa = 6.1 Denaturation form is function loss of native configuration denaturation denaturation peptide bonds not affected H-bonds disulfide bonds ionic bonds L.D.F. disrupted Denaturation 4o structure disrupted first subunits separate 3o structure disrupted protein unfolds 2o structure disrupted H-bonds broken treatments are sometimes reversible renatured sometimes irreversible insulin Denaturing treatments 1. Heat above 50-60oC 2. pH disrupt salt bridges approach pHI frying egg sunburn 3. detergents unfold globular proteins SDS - + - - + Na+ SO4- Denaturing treatments 4. reducing agents oxidizing agents 5. Metal salts S-S Hg+, Pb+, Ag+ SH HS S-Hg O Hg+ C O 6. H-bonding solvents alcohol acetone 7. “Chaotropes” H2N O NH C C urea NH2 H2N NH2 guanidine Words of Wisdom 1. Heat sunburn 6. H-bonding solvents alcohol 3. detergents