Assignment:
This assignment focuses on the protein TMEM16A. Before attempting this assignment, please download and browse through the paper by Lam et al. (2021) (accessible from the URL below).
https://www.nature.com/articles/s41467-020-20787-9
Question 1
(a) What is TMEM16A?
(b) Go to the following webpage(https://www.ncbi.nlm.nih.gov/Structure/pdb/5OYB)and play around with the cryo-electron microscopy structure. Take a time-stamped screen shot of the TMEM16A structure and insert it below.
(c) Is TMEM16A a monomer or a dimer?
(d) What else is shown in the crystal structure?
(e) What ion is TMEM16A permeable to?
(f) What activates TMEM16A? (i.e. what binds to it to make it do its thing)?
(g) Is TMEM16A activated from inside or outside the cell?
In figure 1, the authors perform a series of site-directed mutagenesis experiments on the cDNA coding for TMEM16A, changing codons coding for individual amino acids to alanine. Themutant cDNAs were then expressed in cultured human cells. Patch clamp recordings were then performed on those cells to measure how ions moved across the membrane relative to non-mutated TMEM16A, hence determining the effect of each mutation.
(h) Does the L643A mutation make ion flux easier or harder for the mutant TMEM16A?
(i) Briefly explain your answer to the above.
(j) What do you think would happen if you increased the EGTA concentration in the bath solution by 10-fold?
Figure 2 examines the molecular mechanism of TMEM16A gating properties.
(k) I550, I551, and I641 function as part of the protein's control system. They are found in what part of the protein? (i.e. outer vestibule, neck, inner vestibule etc.)
(l) The sidechains of I550, I551, and I641 can interact with each other. What type of bonding are the amino acid side chains engaged in?
Figure 2b, shows the results of patch clamp experiments measuring the relative current flowing across the membrane in response to increasing concentration of an activating agent.
(m) What effect does the Q649A mutation have on the function of TMEM16A?
(n) Without getting too deep into the mathematical weeds, does the author's model for TMEM16A activation suggest a two-state or more than a two-state mechanism?
(o) Briefly justify your answer to the above.
(p) TMEM16A is involved in one or more human diseases. Using a PubMed search (see URL in Tips and Hints on D2L), identify a paper that describes research on TMEM16A with regard to that disease. State the APA citation for the paper below and include a PMID link.
(q) IN YOUR OWN WORDS, briefly summarize how TMEM16A is involved in that human disease (no more than one paragraph. Do NOT use direct quotes, because it's a lazy style of scientific writing and it will cost you points).
(r) Some FDA-approved drugs are available that interact with TMEM16A. State the name of one of these drugs below.
(s) Postulatethe drug's mechanism of action on TMEM16A, and how it might alleviate symptoms of the disease in question.