Ali Poyan Mehr

Home Institution
Freie Universität Berlin

Host Institution(s)
Yale University School of Medicine, New Haven
Research Mentor: John Forrest, M. D.

E-Mail:
poyanmehr@web.de

Research Topic
see Abstract
Personal Reactions to the U.S. Experience
Spending one year in U.S. to do some research is an experience you should not miss. But, fortunately, experience in science (and maybe barbeque sauce and sneakers) are not the only things you will carry home. Of course, because of my citizenship (Iran), I belonged to "the axis of evil". This circumstance made it a "little bit" difficult for me the get the visa. But as soon as I had it, and entered the US, I didn't experience any of the animosities I expected. Never! Most of the US Americans are extremely polite, which is one of many cultural characteristics I appreciated. And there are also many other things we can learn from. Just go and find out!
Greatest Difficulties Encountered
Taking a look through what other student have written in previous years regarding difficulties, there is nothing I can add. And I don't want to repeat them just because I think there are not really any serious difficulties you will face. Hmm… the greatest difficulty I encountered was finding some souvenirs before going back to Germany. This should give you an impression how easy life can be.
Most humorous incident
During my stay at Mount Desert Island Bio labs in summer, some friends and I bought half a dozen crabs and lobsters to make a big dinner. Of course they were fresh and alive when we left them in the car, inside a plastic bag, just for a short moment. Well, you can guess what happened after we came back. The bags were open, the car flooded with sea water, and we had to find our dinner under the seats and everywhere else they could hide.

Helpful Hints for Future Students

  • My visa application was rejected three times. Don't give up and try hard to get what you want. Of course you will need the help of your mentor for this.
  • Get in touch with other student and international scholars. Feel free to contact me regarding any kind of question you have.
  • Be careful riding a bike, but do it! You can save a lot of money!
  • Put some money into your saving account. It will help you at the beginning.
  • Get your social security number as soon as possible.
  • Be open minded

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Abstract on Research Topic

Mercury sensitivity of shark CFTR is mediated through cysteine residues located in the first transmembrane domain

Authors:
Ali Poyan Mehr and John Forrest, M.D.
Institution:
Department of Nephrology, School of Medicine, Yale University
Purpose:
There are profound differences between mercury inhibition of shark CFTR vs. human CFTR. Cysteine residues (Cys) are the known biding sites for mercury, thus mercury can exhibit its toxic effects on a countless number of proteins. Correlating specific Cys in certain protein domains with mercury toxicity can contribute to the understanding of the function and importance of this domain. Specifically in channel proteins those findings may promote a clearer vision of the three dimensional structure and the arrangement of the pore region of a protein. Both shark and human CFTR share 12 cysteine residues, including three, but in addition the shark homolog has 2 unique in the first transmembrane domain (TMD1) and 2 in the regulatory domain (RD). One or more of these unique Cys residues are most likely mediating the extreme higher sensitivity of sCFTR to mercury versus hCFTR. In order to approach the question, whether the Cys in TMD1 or those in RD are mediating this effect, we constructed chimeric proteins where we replaced the human TMD1 and RD with the shark analogues respectively. Using Xenopus laevis oocytes and TEVC we could explore which part of the shark CFTR carries the mercury sensitivity in to the human CFTR.
Materials and Methods:
Chimeric proteins were constructed using a combination of PCR and restriction enzyme digestion. The TMD1 of shark was amplified using sense primer with an overlapping sequence homolog to the N-terminal end of hCFTR and an antisense primer with an introduced restriction site for BsiW I. The N-terminal end of hCFTR was amplified in a separate step. Both fragments were then combined together in a third reaction. The product was finally combined with the rest of hCFTR, and cloned in to pBlueskript KS(-). Analog to TMD1 the RD was amplified with primer containing BstZ17 I and Hpa I restriction sites and cloned in to hCFTR lacking its own RD. The TMD1 chimeras as well as the wiled types were injected into Xenopus laevis oocytes and TEVC was performed after two to three days of incubation. After a short recovery time in ND96, chloride conductance was activated by adding 10µM forscolin and 1mM isobutylmethylxanthine (IBMX). Once the oocytes reached a plateau (usually after 25 to 35 minutes), HgCl was then added to the solution in a concentration of 1µM.
Results:
From the RD chimera there are not enough data available yet for a statistical analysis, but the degree of inhibition is similar to hCFTR. TMD1 shows the same degree of inhibition like wild type sCFTR (89.20% and 94.58 respectively, p<0.0001).
Conclusion:
Cys residues located in the first transmembrane domain of shark CFTR are likely to be located within the pore forming unit, which is not well described yet. Site specific mutagenesis of those residues will help to find the arrangement of the pore region in more detailed and help to understand the structure-function relationship of CFTR and channel proteins in general.