Hemoglobin
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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




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