Lecture 8: PROTEINS IN ACTION - 2

Question 1

What does deoxyhaemoglobin have?

Answer 1

A dished haem

Question 2

What does oxygen in oxyhemoglobin do?

Answer 2

Flatten the haem and pulls histidine F8 and helix F towards the binding site (increasing its binding affinity for oxygen)

Question 3

What weakens oxygen binding?

Answer 3

Anything that keeps helix F away

Question 4

What does the oxygen in oxyhemoglobin do to the fe2+?

Answer 4

Moves it into the plane of the haem, draws His F8 down and repositions the helix F

Question 5

What are shifts in protein secondary elements called?

Answer 5

Conformation changes

Question 6

What is an example of the conformational change?

Answer 6

Helix F moving relative to helix c

Question 7

Where is the most change observed?

Answer 7

At the FG loop

Question 8

What happens to side chain packing in R and T states?

Answer 8

The interaction between side chains of the F helix and C helix change

Question 9

Positions of side chains in R and T states are both …

Answer 9

stable

Question 10

The transition state between R and T is …

Answer 10

Unstable so not much time is spent in that position

Question 11

Describe the changes when going from R to T conformation?

Answer 11

The F helix moves so that the interaction between threonine and aspartic acid is borked and an interaction with a different threonine and asparagine is formed. This makes the binding pocket larger

Question 12

What is BPG?

Answer 12

2,3-bisphosphoglycerate

Question 13

What is BPG?

Answer 13

An allosteric inhibitor of oxygen binding to haemoglobin

Question 14

What is the charge of BPG?

Answer 14

Highly negatively charged

Question 15

How does BPG bind to deoxyhaemoglobin?

Answer 15

By electrostatic interaction

Question 16

What does BPG do?

Answer 16

Stabilises haemoglobin in the deoxygenated T state, reducing oxygen affintiy

Question 17

When is BPG produced?

Answer 17

During respiration in peripheral tissues, so promotes oxygen release where it is needed

Question 18

When is cooperativity prominent?

Answer 18

Only in presence of allosteric inhibitors of binding

Question 19

What do allosteric inhibitors BPG, CO2 and H+ do?

Answer 19

Stabilise the t state which unmasks cooperativity

Question 20

What happens in the absence of inhibitors?

Answer 20

Stripped haemoglobin is predominantly in the r state so shows little cooperativity (acts almost as myoglobin)

Question 21

What does elevated CO2, and low pH (elevated H+) do?

Answer 21

In metabolising tissues it reduces the affinity of haemoglobin for oxygen, known as the Bohr effect

Question 22

What can CO2 do?

Answer 22

Bind to the extreme N terminal amino group

Question 23

What can H+ do?

Answer 23

Protonate certain amino acid side chains which contributes to stabilising the deoxyhaemoglobin conformation

Question 24

what is the first substantial adaptation to high altitude?

Answer 24

An increase in BPG

Question 25

What does an increase in BPG do?

Answer 25

Reduces haemoglobin oxygen binding

Question 26

What does a rightward shift of the curve do?

Answer 26

Deliver more oxygen to the tissues

Question 27

What do different amino acid sequences of normal haemoglobin subunits in foetus do?

Answer 27

Alter their oxygen binding properties

Question 28

What does foetal haemoglobin include?

Answer 28

Alternate isoforms (epsilon, gamma and zeta) which have higher affinities for oxygen

Question 29

What does foetal haemoglobin allow?

Answer 29

The foetus to capture oxygen in the placenta

Question 30

What does foetal haemoglobin lack?

Answer 30

An amino acid in the BPG binding site so bind BPG less well

Question 31

What is methaemoglobin?

Answer 31

A damaged form of haemoglobin where oxidation of haem fe2+ to Fe3+ shifts one subunit to the R state conformation without oxygen bound

Question 32

How does methaemoglobin impair the function?

Answer 32

The methaemoglobin does not bind oxygen despite otherwise being in the R state because of the Fe3+.
The subunits of the tetramer are shifted to the R state so don’t release oxygen in the tissues as they should

Question 33

What does the enzyme cytochrome b5 reductase do?

Answer 33

regenerates haemoglobin by reducing haemoglobin back to Fe2+ state using transfer of electrons from NADH

Question 34

What are most haemoglobin abnormalities caused by?

Answer 34

Genetic mutations

Question 35

What is the mutation in HbM/Boston haemoglobin?

Answer 35

His E7 mutation to Try E7 changes the environment causing Fe2+ to oxidize to Fe3+

Question 36

What happens as a result of the mutation in HbM/boston haemoglobin?

Answer 36

The haem plane moves slightly, breaking the connection of Fe-HisF8

Question 37

What state is HbM in after the mutation?

Answer 37

It remains in the T state, with low affinity for oxygen as the larger tyrosine blocks some of the binding space

Question 38

What does the sick shape do in sickle cell anaemia?

Answer 38

Means the red blood cells get stuck in blood capillaries which causes a range of secondary debilitating effects in the person

Question 39

What happens to sickled red blood cells?

Answer 39

They become worse at carrying oxygen

Question 40

What is the mutation in sickle cell anaemia?

Answer 40

A gain of function (Hb Beta EGV)

Question 41

What does the beta EGV mutation enable?

Answer 41

Abnormal hydrophobic interactions between Hb molecules, particularly when in the deoxygenated form, causing polymerisation of Hb into chains the distort the red blood cells