BCHM-3050 Lecture Notes - Lecture 10: Partial Pressure, Histidine, Valine
8 Jun 2018
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Department
Course
Professor
Myoglobin and hemoglobin
Myoglobin (mb): monomeric heme proteins
Bind and release oxygen in tissue
○
Common in muscle
○
Away from lungs
○
•
Hemoglobin (Hb): tetrameric heme protein
Transport oxygen from lungs to peripheral tissues and return to
lungs for exhalation
○
Toward lungs
○
•
Physical structure myoglobin v hemoglobin
Myoglobin
Hemoglobin
Single polypeptide
(tertiary structure only)
8 total alpha helices (heme binds b/w E and F
residues)
High oxygen affinity (stores oxygen)
No conformational change
Multiple polypeptide
(quaternary structure)
Tetrameric (4 subunits) = 2
alpha and 2 beta
Each subunit has all
structures but majority of
them are alpha helices that
differ in sequence
Low and high oxygen
affinity (oxygen transport)
High conformational
change (oxygen binds
cooperatively)
Heme is an iron porphyrin
Porphyrin: tetrapyrrole ring system
Mb and hb = Fe (I) ion bound to protoporphyrin IX via 4 N
○
Can also incorporate Cu, Mn, and Co ions
○
•
Apoprotein = Mb/Hb w/o heme
Holoprotein = w/ heme
○
•
With oxygen bound = oxy-
•
w/o oxygen bound = deoxy-
•
Oxygen binds at heme metal ion
Iron (II) has 6 coordinating positions
#2-5: nitrogen's
○
#1: proximal histidine residue (F8 His)
○
#6: oxygen binds
Stabilizes distal histidine (E7 His)
§
○
•
In deoxyhemoglobin:
F8 His pulls Fe out of plane that the ring kept it in previously
○
•
In oxyhemoglobin:
Oxygen pushes Fe back into the plane
○
Greater effect in structural conformation
○
•
Binding in HB and Mb
Taut (T) state: iron popped out of ring plane
Low oxygen state
○
•
Relaxed (R ) state: iron popped back into ring plane
High oxygen state
○
•
Blood oxygen protein with hyperbolic bind curve
Mb: good affinity for oxygen
Strong binding
○
•
As result: mb has poor dissociation of oxygen
Doesn’t want to let go
○
•
Limitations on protein exhibit hyperbolic curve
Strong binding or unloading = efficient but not efficient if both are
together
○
•
Hyperbolic bind curve v sigmoidal bind curve
Sigmoidal: favored
•
Lower P50 = tight binding
Go through conformational change to unload
○
•
Low partial pressure = weak binding
Tissue
○
Unloading
○
•
High partial pressure = strong binding
Lungs
○
Transport
○
•
Model for allosteric transition of hb
How hb goes back and forth between conformations
•
KNF model: binding of oxygen at one subunit changes conformation
Go back and forth between T and R
○
Mixed tetramers
○
•
MWC model: Hb exists in two separate states
No mixed tetramers
○
•
T v R and noncovalent intersubunit interactions
Subtle change in Hb
•
T and R state: interaction b/w alpha and beta dimers
Rotation 15 degree to switch b/w states
○
T state: lose oxygen
Deoxyhemoglobin
§
○
R state: oxygen bound and transported
Oxyhemoglobin
§
○
•
Unfavorable enthalpy loss with the loss of the oxygen
Compensate by favorably binding the oxygen
○
•
Fe-O bonds = strong and stabilize the R state
•
Pulling Fe back into the plane causes steric strain b/w the flat heme, F8His
and Val FG5
Relieved by change in orientation of both His F8 and Val FG5 via
dissoc of oxygen ligand
○
•
Bind of allosteric effectors
Allosteric effector: bind target protein and promote conformational
change
Or prevent it!
○
Help modulate functional properties of protein
○
Ex. Increase/decrease oxygen binding affinity in Hb
○
Homotrophic effect: bind at active sites
Oxygen
Positive
□
Binding increase affinity of oxygen to other hemes in
tetramer
□
§
○
Heterotrophic effect: bind other sites of protein
○
•
Negative allosteric effectors: H+, Co2, 2,3-BPG
Binding of 2 or more effectors decrease binding affinity of oxygen to
hb
○
•
Lungs
Binding of oxygen favors R state
Releases 2,3-BPG, CO2, and H+
§
○
•
Capillaries
Bind 2,3-BPG, CO2 and H+
○
Favors T state and release of oxygen
○
•
Respiring cells
Favor T state
○
•
Negative Heterotrophic
Bind and release of 2,3-BPG, CO2 and H+
Negative effectors stabilize T state
○
•
2,3-BPG: bind in cleft that opens in the T state
Favor T state
○
Greater oxygen delivery
○
Low oxygen binding
○
Fetal mb mutation: His 143 becomes Ser143
Reduce BPG binding affinity
§
○
•
BOHR effect: as pH drops, H+ bind to Hb favors T state
Oxygen delivery increases
○
Low oxygen binding
○
•
CO2: bind to Hb in the N terminus as carbonate
Bind results in H+ production
○
Favor R state
○
•
Evolution and Protein
Beta chain of Hb = glutamate becomes valine
Nonconservative mutation
○
Cause sickle cell
○
•
Chapter 7: Protein function
Tuesday, June 5, 2018
5:06 PM
Myoglobin and hemoglobin
Myoglobin (mb): monomeric heme proteins
Bind and release oxygen in tissue
○
Common in muscle
○
Away from lungs
○
•
Hemoglobin (Hb): tetrameric heme protein
Transport oxygen from lungs to peripheral tissues and return to
lungs for exhalation
○
Toward lungs
○
•
Physical structure myoglobin v hemoglobin
Myoglobin Hemoglobin
Single polypeptide
(tertiary structure only)
8 total alpha helices (heme binds b/w E and F
residues)
High oxygen affinity (stores oxygen)
No conformational change
Multiple polypeptide
(quaternary structure)
Tetrameric (4 subunits) = 2
alpha and 2 beta
Each subunit has all
structures but majority of
them are alpha helices that
differ in sequence
Low and high oxygen
affinity (oxygen transport)
High conformational
change (oxygen binds
cooperatively)
Heme is an iron porphyrin
Porphyrin: tetrapyrrole ring system
Mb and hb = Fe (I) ion bound to protoporphyrin IX via 4 N
○
Can also incorporate Cu, Mn, and Co ions
○
•
Apoprotein = Mb/Hb w/o heme
Holoprotein = w/ heme
○
•
With oxygen bound = oxy-
•
w/o oxygen bound = deoxy-
•
Oxygen binds at heme metal ion
Iron (II) has 6 coordinating positions
#2-5: nitrogen's
○
#1: proximal histidine residue (F8 His)
○
#6: oxygen binds
Stabilizes distal histidine (E7 His)
§
○
•
In deoxyhemoglobin:
F8 His pulls Fe out of plane that the ring kept it in previously
○
•
In oxyhemoglobin:
Oxygen pushes Fe back into the plane
○
Greater effect in structural conformation
○
•
Binding in HB and Mb
Taut (T) state: iron popped out of ring plane
Low oxygen state
○
•
Relaxed (R ) state: iron popped back into ring plane
High oxygen state
○
•
Blood oxygen protein with hyperbolic bind curve
Mb: good affinity for oxygen
Strong binding
○
•
As result: mb has poor dissociation of oxygen
Doesn’t want to let go
○
•
Limitations on protein exhibit hyperbolic curve
Strong binding or unloading = efficient but not efficient if both are
together
○
•
Hyperbolic bind curve v sigmoidal bind curve
Sigmoidal: favored
•
Lower P50 = tight binding
Go through conformational change to unload
○
•
Low partial pressure = weak binding
Tissue
○
Unloading
○
•
High partial pressure = strong binding
Lungs
○
Transport
○
•
Model for allosteric transition of hb
How hb goes back and forth between conformations
•
KNF model: binding of oxygen at one subunit changes conformation
Go back and forth between T and R
○
Mixed tetramers
○
•
MWC model: Hb exists in two separate states
No mixed tetramers
○
•
T v R and noncovalent intersubunit interactions
Subtle change in Hb
•
T and R state: interaction b/w alpha and beta dimers
Rotation 15 degree to switch b/w states
○
T state: lose oxygen
Deoxyhemoglobin
§
○
R state: oxygen bound and transported
Oxyhemoglobin
§
○
•
Unfavorable enthalpy loss with the loss of the oxygen
Compensate by favorably binding the oxygen
○
•
Fe-O bonds = strong and stabilize the R state
•
Pulling Fe back into the plane causes steric strain b/w the flat heme, F8His
and Val FG5
Relieved by change in orientation of both His F8 and Val FG5 via
dissoc of oxygen ligand
○
•
Bind of allosteric effectors
Allosteric effector: bind target protein and promote conformational
change
Or prevent it!
○
Help modulate functional properties of protein
○
Ex. Increase/decrease oxygen binding affinity in Hb
○
Homotrophic effect: bind at active sites
Oxygen
Positive
□
Binding increase affinity of oxygen to other hemes in
tetramer
□
§
○
Heterotrophic effect: bind other sites of protein
○
•
Negative allosteric effectors: H+, Co2, 2,3-BPG
Binding of 2 or more effectors decrease binding affinity of oxygen to
hb
○
•
Lungs
Binding of oxygen favors R state
Releases 2,3-BPG, CO2, and H+
§
○
•
Capillaries
Bind 2,3-BPG, CO2 and H+
○
Favors T state and release of oxygen
○
•
Respiring cells
Favor T state
○
•
Negative Heterotrophic
Bind and release of 2,3-BPG, CO2 and H+
Negative effectors stabilize T state
○
•
2,3-BPG: bind in cleft that opens in the T state
Favor T state
○
Greater oxygen delivery
○
Low oxygen binding
○
Fetal mb mutation: His 143 becomes Ser143
Reduce BPG binding affinity
§
○
•
BOHR effect: as pH drops, H+ bind to Hb favors T state
Oxygen delivery increases
○
Low oxygen binding
○
•
CO2: bind to Hb in the N terminus as carbonate
Bind results in H+ production
○
Favor R state
○
•
Evolution and Protein
Beta chain of Hb = glutamate becomes valine
Nonconservative mutation
○
Cause sickle cell
○
•
Chapter 7: Protein function
Tuesday, June 5, 2018 5:06 PM
Document Summary
Transport oxygen from lungs to peripheral tissues and return to lungs for exhalation. 8 total alpha helices (heme binds b/w e and f residues) Tetrameric (4 subunits) = 2 alpha and 2 beta. Each subunit has all structures but majority of them are alpha helices that differ in sequence. Mb and hb = fe (i) ion bound to protoporphyrin ix via 4 n. Can also incorporate cu, mn, and co ions. With oxygen bound = oxy- w/o oxygen bound = deoxy- F8 his pulls fe out of plane that the ring kept it in previously. Taut (t) state: iron popped out of ring plane. Relaxed (r ) state: iron popped back into ring plane. As result: mb has poor dissociation of oxygen. Strong binding or unloading = efficient but not efficient if both are together. How hb goes back and forth between conformations. Knf model: binding of oxygen at one subunit changes conformation.
