Assignment 4 |
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Assignment 4
Science News has a relevant article for all students learning about biosignaling. Go to http://sciencenow.sciencemag.org/cgi/content/full/2008/1031/1 and answer the following questions.
1. What is the function of myosin V that is related to learning?
2. What activates the myosin?
3. How does the activator enter the cell? (Hint: Consider what we've been studying and suggest a specific protein involved in biosignaling.)
4. Although this brief article isn't specific about the activator-myosin interaction, it may well be mediated by calmodulin (CaM). Go to http://www.rcsb.org/pdb/explore.do?structureId=2IX7 at the protein data bank to see a complex between myosin and CaM. The abstract states that "calmodulin is bound to the first two IQ motifs of myosin V". Since the authors of the article had no idea that myosin would be implicated in the learning process, what did they mean by "IQ motifs"?
5. If you click on the second M on the structure page for 2IX7, you should find the article written when calmodulin was the Molecule of the Month (the first M is about anthrax toxin). Read the second page to find out what is unusual about the binding of CaM to its target proteins. What type of interaction is involved? How specific is it?
This is due at the beginning of class on Monday, Nov. 3. Answers must be turned in individually. As always, I encourage brief answers.
Answers:
1. Myosin V moves "packets of receptors" to the cell membrane, so that the receptors can bind to neurotransmitters. This is all within a neuron.
2. Ca2+ activates the myosin.
3. In response to a signal (such as acetylcholine), an ion channel, such as the acetylcholine receptor, opens, allowing Ca2+ to enter the cell. It's most likely a voltage-gated ion channel.
4. Motifs containing isoleucine and glutamine.
5. The interaction is between nonpolar residues, so it would be a hydrophobic interaction that is not very specific. I discovered while grading that most people just wrote nonpolar interaction, which is correct. If you made the connection that this is a hydrophobic interaction, you got a bonus half point.
Most of you are making a commendable effort to interpret the question and the reading, so that your answer can be brief and to the point. A few people are continuing to answer by quoting extensively from the reading. Such answers will receive half credit in the future. Yes, I know there's only one assignment remaining, according to the syllabus. If I see a good topic, though, I'll add an extra assignment and then drop the lowest assignment score.