Protein Physics

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Protein Physics

• A. V. Finkelstein
• O. B. Ptitsyn
• LECTURE 11
• www.nd.edu/aasztalo

Andrea Asztalos, 2007 August 22
collagen
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One classification of proteins
1.Fibrous Proteins

• mostly structural proteins
• maintain a rigid/flexible structure
• an elongated, unidimensional structure
• most of them are insoluble
• high helix or beta sheet content
• Ex a-keratin, collagen, myosin, actin,

2.Membrane Proteins

• reside within the cellular intracellular
  membrane
• transport molecules in and out of the cell
• Ex membrane associated enzymes, porin

3.Globular Proteins

• short chains packed into a compact 25-40Å
  globule
• closely folded structure
• water soluble proteins
• Ex egg albumin, hemoglobin, many enzymes

Other classifications SCOP, PANTHER
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Fibrous proteins Silk Fibroin

• strong, chemically inert, insoluble
• ß-structural protein
• repeating octamer (Gly, Ala) in the
• primary structure, interrupted by
• regions containing bulkier residues

Packed ß-sheets
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Fibrous proteins a-keratin
Found in hair, horn, nail, tail, feather

• strong, chemically inert, insoluble
• a-structural protein
• repeating heptamer in the primary
• structure
• similar structure in myosin, tropomyosin

Held together by Hydrophobic interactions
Tropomyosin mid-region
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Helix Packing

• the surface of the helix consists of grooves
• and ridges, like a screw thread

• 2 helices can be packed when a ridge from
• each fits into the others groove

• the two interface areas should have
• complementary surfaces

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Fibrous proteins Collagen
Structural protein of bones, skin, tendons and
ligaments

• strong, insoluble and chemically inert
• superhelix composed of three helices (1000
  residues)
• main motif a triad of residues
• Gly faces the center essential for H-bonding
• boiled, the triple helix is destroyed -gt gelatin
• in helices we have found intra-chain H-bonds,
• in collagen H-bonds are between different
  chains
• mutations Gly replaced by another residue,

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Differences between Collagen and keratin
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Collagen Fibrils the next higher structural
level
Collagen superhelices associate into collagen
fibrils
Fibrils are strengthened by intrachain Lys-Lys
and interchain Hydroxy-pyridinium crosslinks
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Fibrous proteins Elastin matrix protein
Abundant in ligaments, lungs, skin, artery walls

• flexible, insoluble
• 1/3 of Gly, 1/3 of AlaVal,
• many Pro, but no HyPro
• lacks regular secondary structure
• arranged in relaxed coils
• elastin chains are higly cross-linked
• into 3D network of fibers, in which
• other more structural proteins
• are immersed