BCHM 10000 Lecture Notes - Lecture 27: Myoglobin, Protein Aggregation, Hemoglobin

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3 Jul 2018

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Hemoglobin

●Myoglobin facilitates diffusion of O2 in muscle tissue

– O2 solubility in aqueous solution limits respiration in active muscle tissue

– Myoglobin increases effective O2 solubility in muscle and promotes diffusion

from capillaries to mitochondria.

●Hemoglobin binds O2 in lungs and transports it to peripheral tissues.

●Myoglobin is a monomeric protein

●Myoglobin and the subunits of hemoglobin share a common “fold” (the globin fold) even

though their overall sequence identity is quite low

●The oxygen binding curves for myoglobin and hemoglobin are very different and

facilitate oxygen transport to muscles

●Hemoglobin exhibits cooperative oxygen binding (sigmoidal curve)

●Cooperativity comes about in a multimeric protein when the binding of one ligand

molecule increases the protein’s affinity for the binding of a second ligand molecule

●O2 binding alters electronic state of Fe(II) so that it can now fit within heme

●O2 binding moves proximal His and the F-helix that contains it

●O2 binding alters electronic state of Fe(II) so that it can now fit within heme

●O2 binding moves proximal His and the F-helix that contains it

●The F-helix tilts and moves across the heme plane

●O2 binding alters electronic state of Fe(II) so that it can now fit within heme

●O2 binding moves proximal His and the F-helix that contains it

●The F-helix tilts and moves across the heme plane

●F-helix movement induces changes at the α–β interface and ultimately the quaternary

structure of hemoglobin

●Conformational changes are reversed when oxygen dissociates in muscle

●Conformational changes in HbS upon oxygen unloading expose interaction sites for Val6

and lead to aggregations

●Conformational changes in HbS upon oxygen unloading expose interaction sites for Val6

and lead to aggregation

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Document Summary

Myoglobin facilitates diffusion of o2 in muscle tissue. O2 solubility in aqueous solution limits respiration in active muscle tissue. Myoglobin increases effective o2 solubility in muscle and promotes diffusion from capillaries to mitochondria. Hemoglobin binds o2 in lungs and transports it to peripheral tissues. Myoglobin and the subunits of hemoglobin share a common fold (the globin fold) even though their overall sequence identity is quite low. The oxygen binding curves for myoglobin and hemoglobin are very different and facilitate oxygen transport to muscles. Hemoglobin exhibits cooperative oxygen binding (sigmoidal curve) Cooperativity comes about in a multimeric protein when the binding of one ligand molecule increases the protein"s affinity for the binding of a second ligand molecule. O2 binding alters electronic state of fe(ii) so that it can now fit within heme. O2 binding moves proximal his and the f-helix that contains it. The f-helix tilts and moves across the heme plane.

Related Questions

1. The dominant motif found in hemoglobin and myoglobin is: a) twisted beta sheet b) beta barrel c) helix-loop-helix d) 7-TM 2. Myoglobin has how many polypeptide chains? A) 1 b) 2 c) 3 d) 4 3. Structurally and functionally, hemoglobin closely resembles a(n) a) transmembrane protein b) mucopolysaccharide c) bile salt d) allosteric enzyme 4. The oxygen binding site in hemoglobin and myoglobin is called: a) BPG b) heme c) proximal-His d) N-terminal carbamate 5. The proximal His residue in hemoglobin and myoglobin binds to which atom or molecule? A) CO2 b) O2 c) Fe d) BPG 6. The distal His residue in hemoglobin and myoglobin binds to which atom or molecule? A) CO2 b) O2 c) Fe d) BPG 7. BPG binds to: a) N-terminal carbamate b) proximal His c) heme group d) central cavity 8. Indirect activity of CO2 is a result of increased concentration of which chemical species? A) BPG b) H+ c) heme iron d) distal His 9. Direct activity of CO2 is a result of binding to which molecular feature? A) the heme group b) the N-terminal ends of the 4 polypeptide chains c) the central cavity d) the proximal His 10. The sigmoidal, cooperative binding curve commonly observed for hemoglobin is a result of: a) competition between CO2 and O2 for heme binding. B) competition between heme and distal His for O2 binding c) competition between BPG and CO2 for binding at the central cavity site d) T to R transition 11. Hemoglobin has a tendency to release its oxygen to the tissues because: a) in this region pH is high and O2 concentrations are low b) in this region both pH and O2 concentrations are low c) in this region both pH and O2 concentrations are high d) there is much BPG in this region 12. Which statement about fetal hemoglobin is not true? A) fetal hemoglobin has gamma chains instead of beta chains b) fetal hemoglobin binds BPG less strongly than maternal hemoglobin c) fetal hemoglobin binds oxygen less strongly than maternal hemoglobin d) fetal hemoglobin binds oxygen more strongly than maternal hemoglobin 13. Which process is most responsible for the sickling of cells seen in sickle cell disease? A) aggregation of the oxygenated R form of hemoglobin-S to form insoluble fibers b) aggregation of the deoxygenated T form of hemoglobin-S to form insoluble fibers c) Hemoglobin-S does not contain heme d) Hemoglobin-S contains a mutant form of heme which will not bind oxygen 14. A person with sickle-cell trait is very unlikely to catch which disease? A) malaria b) colon cancer c) avian flu d) whooping cough 15. A person with a genetic defect which results in the synthesis of an insufficient amount of the alpha chain of hemoglobin is said to have which disease? A) alpha thalassemia b) beta thalassemia c) pernicious anemia d) Crohnâs disease

Match the words (A-E) with the statements below: ( 10 pts)

A. Bohr

B. 2, 3-BPG

C. Carbamate

D. Carbon dioxide

E. Concerted

F. Distal Histidine

G. Heme

H. Hemoglobin

I. Myoglobin

J. Sickle Cell Anemia

This has the ability to protect against carbon monoxide binding to the heme _______________

This is the molecule whose function is to facilitate diffusion of oxygen in muscle cells. ___________

The ability of myoglobin to bind oxygen depends on the presence of a bound prosthetic group called .

The shape of this protein has a sigmoidal curve _______________

As the partial pressure of ___________ increases, the affinity of oxygen binding to hemoglobin decreases. (there can be two answers)

The effect of hydrogen ions and carbon dioxide on the binding of oxygen to hemoglobin is called the _____________ effect

___________ is an allosteric effector that binds to the positive charges on the hemoglobin molecule .

Hemoglobin binding of oxygen is best described as a combination of sequential and ______________ model.

Carbon dioxide forms ______________ groups in proteins by reaction with N-terminal groups.

This condition is a result of a single-point mutation in the Î² chain of hemoglobin:__________________

BCHM 10000 Lecture Notes - Lecture 27: Myoglobin, Protein Aggregation, Hemoglobin

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