Assume that a new oxygen-transport protein has been discovered in certain invert
ID: 537278 • Letter: A
Question
Assume that a new oxygen-transport protein has been discovered in certain invertebrate animals. X-ray diffraction of the deoxy protein reveals that it has the dimeric structure shown in the figure below in panel (a) with a salt bridge between residues histidine 13 and aspartic acid 85. The two monomers interact by salt bridges between the C- and N-termini. The O2-binding site lies between the two iron atoms shown, which are rigidly linked to helices A and C (see panel (b)). In the deoxy form, the space between the iron atoms is too small to hold O2, and so the Fe atoms must be forced apart when O2 is bound.
Answer the following questions, explaining your answer in each case in terms of the structure shown below. Note: It is a dimer so that cooperativity might occur!
Predict the likely effect of a mutation that replaced aspartic acid 85 by a lysine residue. (Three correct answer) Hint: one of the correct answerrs is "The whole structure would become unstable".
Check all that apply.
1. The molecule would exhibit higher O2 affinity. 2. The whole structure would become more stable. 3. The molecule would exhibit lesser cooperativity. 4. The whole structure would become unstable. 5. The molecule would exhibit higher cooperativity. 6. The molecule would exhibit lower O2 affinity. Helix Helix Fe Fe a 13 13 e Fe Oxygen molecule Helix Helix Helix Helix (a) Structure of deoxy protein (b)Detail of the oxygen-binding N and C denote N-termini site in the oxyform. and C-termini. The dyad axis (c) is perpendicular to this page.Explanation / Answer
The whole molecule would become unstable.
The molecule will exhibit higher cooperativity.
The molecule will exhibit lower O2 affinity.
This might be due to the fact that lysine is a basic amino acid and so it can donate more electron density to Fe atoms. As a result Fe will not bind with O2 for getting electron density from O2.
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