F08 LS1a Pset 9keyfinal

F08 LS1a Pset 9keyfinal - Name: TF Name: LS1a Problem Set...

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TF Name: 1 LS1a Problem Set #9 Due Monday 12/8 at noon in your TF’s drop box on the 2 nd floor of the Science Center (100 points) 1. (26 points) The structure of HIV protease is stable from pH 3-7; however, the activity of the enzyme varies within this range as shown below. a) Based on your understanding of catalysis by HIV protease, explain this relationship between protease activity and pH. You can assume that the tertiary and quaternary structures of the enzyme remain relatively stable between pH 3 and 7. (8 points) The catalytic mechanism of HIV protease requires one protonated Asp and one deprotonated Asp. The pKa of Asp is approximately 3.9. At low pH (below 3.9), both Asp's are protonated, so no general base catalysis is possible. At higher pH (above 3.9), both Asp's are deprotonated, so no general acid catalysis is possible. b) What would be the consequence of mutating the catalytic Asp 25 into Asn? Assume substrate binding and protease structure are not affected by the mutation. (6 points) Mutation of Asp 25 into Asn would cause a loss of catalytic activity since the Asn would be unable to mediate base catalysis. c) What would be the consequence of mutating the catalytic Asp 25’ to Asn? Assume substrate binding and protease structure are not affected by the mutation. (6 points) Mutation of Asp 25’ into Asn would cause a loss of catalytic activity since the Asn would be unable to mediate acid catalysis. d) What would be the consequence of mutating Ile 50 to Gly? Assume substrate binding and protease structure are not affected by the mutation. (6 points) There would likely be no effect on catalysis since it's the backbone of Ile 50 that coordinates the water. Protease activity
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F08 LS1a Pset 9keyfinal - Name: TF Name: LS1a Problem Set...

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