Structure of Proteins 3D structure determined by amino acid sequence Structure - Function Native...
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![Page 1: Structure of Proteins 3D structure determined by amino acid sequence Structure - Function Native structure of a protein = functionally, folded conformation.](https://reader035.fdocuments.net/reader035/viewer/2022062300/56649c9e5503460f9495dfd8/html5/thumbnails/1.jpg)
Structure of Proteins
3D structure determined by amino acid sequenceStructure - FunctionNative structure of a protein = functionally, folded conformation
Protein conformation stabilized by 1. disulfide bonds 2. weak noncovalent interactions (H-bonds, hydrophobic & ionic)
Chymotrypin Glycine
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3D Structure of Proteins
Primary structure = amino acids linked togetherPeptide bond is rigid and planar
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Secondary Structure of Proteins
Helices
H-bond
Important elements - steric clashes & H-bonding
Basic types of secondary structure: Helices, Sheets, Turns and Coils
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Secondary Structure of Proteins Helices Ionic interaction between R groups of AAs three residues apart
Arg
Asp
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Secondary Structure of Proteins sheetsBackbone is extended into a zigzag structureArranged side-by-side to form a structure (pleats)Important Forces = H-bonds and steric clash
Layering of >2 sheets R groups must be small (Gly, Ala)
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Secondary Structure of Proteins turnsOccur frequently in globular proteins, 180˚ turn involving 4 AasUsed to:1. Reverse direction of polypeptide chain2. Connect helices/ sheets and within sheets
Important forces:
Amino acids used:Gly - because it is small and flexiblePro - because of cis conformation of peptide bond forms a tight turn
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Secondary Structure of Proteins
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Tertiary Structure
Overall 3D arrangement of all atoms in a proteinLong range contacts between AAs in a single polypeptide chain
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Quarternary Structure
Long range contacts between AAs in a different polypeptide chain
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Fibrous Proteins
Mainly structural role
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Fibrous Proteins
-KeratinsFound in: mammals, provide strengthHair, wool, nails, claws, quills, horns, hooves, skin
Strengthened by:Disulfide bonds
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Fibrous Proteins
-KeratinsPermanent waving of hair1. Reduce disulfide bonds2. Moist heat breaks H-bonds and causes uncoiling of helix3. Remove reducing agent, add oxidizing agent, new S-S bonds
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Fibrous ProteinsCollagen helices, left-handed helix with 3 amino acids per turn
35% Gly, 11% Ala, 21% Pro/4-Hyp(Gly-X-Y) repeat with X as Pro and Y as 4-HypCoiled-coil, three separate polypeptides called chains are supertwisted
Provide strength (stronger than ??)Connective tissue (tendons, cartilage, organic matrix of bone, cornea)
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Fibrous Proteins
Collagen
Rigid and brittle bones caused by:Crosslinks in collagen fibrils over time
Gly-X-Y repeat important - single change results in disease
Osteogenesis imperfecta - abnormal bone formation in babiesEhlers-Danlos syndrome - loose joints
Both diseases involve: mutation of Gly to a different amino acid
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Fibrous Proteins
SilkFibrous protein of silk = FibroinSecondary structure present: sheetsForces involved: H-bonds between different sheets
Made by: insects and spidersSilk does not stretch because it is already highly extended
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Fibrous vs. Globular Proteins
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Globular Proteins
helices and sheets and turns and ………noncovalent interactions
Arrangement of different secondary structural elements:Compact conformationFolding provides structural diversity
Globular proteins = enzymes, transport proteins, motor proteins, regulatory proteins, immunoglobulins, etc.
First understanding of globular proteins came from: x-ray structure of myoglobin (oxygen-binding protein in muscle)
Iron protoporphyrin (heme)
Single polypeptide chain
helix
turn
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Globular Proteins
Other important forces in globular proteins:Hydrophobic interactions
Hydrophobic aa
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Globular Proteins
Well-studied example: MyoglobinFlat heme group rests in crevice of protein
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Globular Proteins
Variety of Tertiary Structures
Respiratory chain in mitochondria
Heme
Egg white and human tearsCleaves polysaccharides
Disulfide bond
Disulfide bond
Enzyme secreted by pancreasHydrolyzes RNA
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Protein Denaturation & FoldingAA sequence determines tertiary structure
Importance of native structureLoss of structure = loss of function
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Protein Denaturation & FoldingRapid stepwise folding
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Protein Denaturation & Folding
Defects in folding may lead to disease
AA mutation in CFTR - cystic fibrosis
BUT No AA mutation (except in inherited forms) just misfolding in (PrP) Prion Protein
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Protein Denaturation & Folding
Proteins undergo assisted folding“molecular chaperones” assist in folding