Lecture 9 - Protein Ligand Interactions Flashcards
What does myoglobin do?
Stores molecular oxygen in tissue
Hemoglobin transports molecular oxygen from ________ to _________, then transports CO2 from ________ to _________.
Lung to tissue
Tissue to lung
How many hemoglobin monomers are there?
4: α1, α2, β1, β2
Where is a heme group bound in each polypeptide chain?
Between helix E and F
How many amino acid residues are there in a single polypeptide chain of myoglobin?
153
Describe the structure of myoglobin
Tertiary structure of 8 right-handed α-helices with a hydrophobic pocket, which forms a protective sheath for a heme group with iron atom in the middle
In terms of myoglobin properties, what happens during periods of oxygen depletion?
Oxy-myoglobin releases its bound oxygen which is then used in metabolism
True or false? Secondary structure of myoglobin is unusual
True
True or false? Secondary structure of myoglobin is typical of water soluble globular protein.
False, TERTIARY not secondary
The oxygen carried by heme-proteins (both myoglobin and hemoglobin) is bound directly to what??
To the ferrous iron atom of the heme prosthetic group
True or false? Fe2+ is tetrahedral coordinated in myoglobin and hemoglobin
FALSE, OCTAHEDRAL not tetrahedral
CO binds to free heme how many times better than O2? And how many times better than O2 to hemoglobin?
20,000 times
250 times
What is he difference between the binding of O2 and CO to a free heme?
O2 binds to free heme at an angle whereas CO binds to free heme perpendicular to heme plane
Describe the structure of hemoglobin
Tetramer of four polypeptide chains
Two identical α chains (141 AA residues) and two identical β chains (146 AA residues)
Each chain has a heme group, hence four O2 can bind to each Hb
How many identical AA residues do the three polypeptide chains of Mb, α-Hb, and β-Hb have?
27
A protein in which the binding of a ligand at one binding site affects the binding properties of another site in the same protein
Allosteric protein
True or false? When the first O2 molecule binds to the first subunit of completely deoxygenated hemoglobin, this binding decreases the affinity of the remaining hemoglobin subunits for O2.
FALSE, it INCREASES the affinity
True or false? As additional O2 is bound to the second and third subunits of hemoglobin, O2 binding is further strengthened, incrementally
TRUE
Monomeric myoglobin has how many O2 binding affinity?
Only ONE
The α1-β1 (and α2-β2) interface involves more than ____ residues, but the α1-β2 (and α2-β1) involve only ____ residues
30
19
What is the tense (T) state?
The tertiary configuration of low affinity, deoxygenated hemoglobin
What is the relaxed (R) state?
The quaternary structure of the fully oxygenated high affinity form of hemoglobin
What is the difference between the curve of oxygen binding to myoglobin versus the oxygen binding to hemoglobin?
O2 binding to myoglobin is linear
O2 binding to hemoglobin has 3 phases: hemoglobin, Hb high affinity state, and Hb low affinity state
Where does the CO2 bind to deoxy-Hb?
At the amino-terminal end of each globin chain
