Hemoglobin

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 Anfinsens 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

• Hsps
• 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