Last Lecture: Structure Determination

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Last Lecture Structure Determination Today
Structure Determination, Heme Proteins Mid-term
to end of lecture 9 (last Monday) Bring
Molecular model Review, Q/A Monday Feb. 5 MSB
Rm2-27 530-730

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1D 1H Spectrum of Protein
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2D-NMR Spectrum (1H-1H NMR)
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2D-NMR Spectrum (15N- 1H NMR)
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Nuclear Overhauser Effect (NOE)
-relaxation by through space transfer
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Detail of 2D Spectrum
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Set of NMR Derived Structures
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Protein Function
Structure cellular architecture Carriers
transport Enzymes Catalysis
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Oxygen Transport and Storage Hemoglobin and
Myoglobin
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Hemoglobin and Human Disease
-Sickle Cell b chain E6 to V6
-b thalassemia imbalance in a to b ratio
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Binding of Oxygen to Myoglobin
1 torr 133 Pa 0.132 atm
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Structural Features of Hb
1. Hb is a tetramer (4 subunits) a2b2 2. One
heme bound per subunit 3. Each heme binds one
O2 4. Hb exists in 2 states T deoxy Hb R
oxy Hb 5. T state is stabilized by intrasubunit
and intersubunit salt bridges 6. Conversion T
R involves breaking salt bridges 7. T R is
also characterized by changes in a1 b2
(a2 b1)contacts subunits move closer
together to expel 2,3 BPG 8. More extensive
contacts remain unchanged a1 b2 a2 b1

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Oxygen Binding Curves
hyperbolic (My) and sigmoidal (Hb)
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Four Factors Affect O2 Binding to Hb
Hb stripped of these factors has high O2
affinity, P50 12 torr little cooperativity
(hyperbolic O2 binding curve) H ions bind to
deoxyHb and stabilize it Cl- ions also
stabilize deoxyHb BPG (2,3-bisphosphoglycerate)
binds to deoxyHb preferentially CO2
binds to deoxyHb preferentially All 4 of these
factors stimulate Hb to release its bound O2 in
the capillaries by reducing the O2 binding
affinity
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Oxygen Transfer Between Hemoglobins
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Myoglobin
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Structure of DeoxyHb
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Structure of OxyHb
a2
b1
a1
b2
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T to R Transition in Hemoglobin
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(oxy)
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Specific Binding of Bisphosphoglycerate to
Hemoglobin