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Hemoglobin

Hemoglobin . tetramer of globins (like myoglobin), or dimer of  protomers. Myglobin. Eight -helical segments Heme. fig 6-16a. fig 7-3. fig 6-23. Identical subunits arrayed symmetrically. Helical TMV 2130 identical subunits Rotational Hemoglobin C 2 symmetry 2 subunits

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Hemoglobin

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  1. Hemoglobin • tetramer of globins (like myoglobin), or • dimer of  protomers

  2. Myglobin • Eight -helical segments • Heme

  3. fig 6-16a

  4. fig 7-3

  5. fig 6-23

  6. Identical subunits arrayed symmetrically • Helical • TMV 2130 identical subunits • Rotational • Hemoglobin C2 symmetry 2 subunits • Poliovirus I symmetry (icosahedral) 60 subunits • 30 edges = 20 faces + 12 vertices - 2

  7. fig 6-25b

  8. fig 6-24c

  9. fig 6-25a

  10. Factors favoring polymers • Coding capacity of nucleic acids in viruses • size of code for one aa is 4 base pairs • Error rate is ~ 0.01%

  11. Tertiary Structure determined by primary structure • Christian Anfinsen’s experiment with RNAse • RNAse + chaotropic agent (urea) + C2H5SH  denatured (unfolded) protein; loss of catalytic activity • denatured (unfolded) protein - urea, C2H5SH  native (refolded) protein; full activity

  12. fig 6-27

  13. Protein Folding • Cell is densely packed with proteins • in vitro may be easier than in vivo • Active Research area for years • Current model: • Combination of “molten globule” (hydrophobic interaction stabilized organization and pre-formation of local secondary structures followed by supersecondary structures and whole domain

  14. Assisted Folding • PDI • Protein disulfide isomerase • catalyzes reshuffling of disulfide bonds • PPI • peptide prolyl isomerase • catalyzes cis-trans isomerization of prolines

  15. Chaperones • Hsp’s • Originally identified as protectants against high temperatures

  16. fig 6-30

  17. Chaperonins • GroEL/GroES system • up to 15% of E. Coli proteins • up to 30% under heat stress

  18. fig 6-31

  19. fig 6-31a

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