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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
Hemoglobin
  • tetramer of globins (like myoglobin), or
  • dimer of  protomers
myglobin
Myglobin
  • Eight -helical segments
  • Heme
identical subunits arrayed symmetrically
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
factors favoring polymers
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%
tertiary structure determined by primary structure
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
protein folding
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
assisted folding
Assisted Folding
  • PDI
    • Protein disulfide isomerase
      • catalyzes reshuffling of disulfide bonds
  • PPI
    • peptide prolyl isomerase
      • catalyzes cis-trans isomerization of prolines
chaperones
Chaperones
  • Hsp’s
    • Originally identified as protectants against high temperatures
chaperonins
Chaperonins
  • GroEL/GroES system
    • up to 15% of E. Coli proteins
    • up to 30% under heat stress