Thaler, Tracey Lyn.
Search for Extraterrestrial Life using Chiral Molecules: Mandelate Racemase as a Test Case.
Degree: PhD, Chemistry and Biochemistry, 2007, Georgia Tech
The possible existence of extraterrestrial life forms has been of interest to humans for many millennia. In the past few decades space travel has provided an opportunity to search life outside of Earth. Chiral molecules are critical molecules in Earth-based life and are among the first chemical molecules sought after as proof of potential extraterrestrial life; however, identification of these chiral molecules is difficult due the lack of sensitive instruments. The objective of this work is to develop a benchmark reaction to be used as a guide in the development of instrumentation, such as a polarimeter, to be used in the search for extraterrestrial life. To achieve this objective, to investigate the enzyme mandelate racemase (MR), which catalyzes the racemization between the enantiomers of mandelate. MR is a member of the enolase superfamily, which contains a (alpha/beta)7-b barrel domain, the fold most frequently found among all known protein structures.
Activity of the enzyme was measured at low temperatures and in non-aqueous media, as these are the conditions that represent extraterrestrial terrain. We find that mandelate racemase (MR) is active in concentrated ammonium salt solutions and water-in-oil microemulsions in a temperature range between 30C to 70C; however, the enzyme is not active in several organic cryosolvents. The stability of the structure of MR was also explored. Using differential scanning calorimetry (DSC) we observe the unfolding of the enzyme was irreversible and therefore kinetically controlled. We also found proof for divergent evolution of the enolase superfamily, providing evidence for divergent evolution across the MR and muconate lactonizing enzyme (MLE) subfamilies has been demonstrated. However, we also conclude that reactions yielding a polarimetric signal, such as racemizations employed in this work, are suitable as a tool to find signs of life.
Advisors/Committee Members: Andreas Bommarius (Committee Chair), Christoph Fahrni (Committee Member), Donald Doyle (Committee Member), Phillip Gibbs (Committee Member), Rick Trebino (Committee Member).
Subjects/Keywords: Irreversible protein denaturation; Enzymatic reactivity at subzero temperatures; Enolase superfamily; Polarimetric assay
to Zotero / EndNote / Reference
APA (6th Edition):
Thaler, T. L. (2007). Search for Extraterrestrial Life using Chiral Molecules: Mandelate Racemase as a Test Case. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/14527
Chicago Manual of Style (16th Edition):
Thaler, Tracey Lyn. “Search for Extraterrestrial Life using Chiral Molecules: Mandelate Racemase as a Test Case.” 2007. Doctoral Dissertation, Georgia Tech. Accessed November 27, 2020.
MLA Handbook (7th Edition):
Thaler, Tracey Lyn. “Search for Extraterrestrial Life using Chiral Molecules: Mandelate Racemase as a Test Case.” 2007. Web. 27 Nov 2020.
Thaler TL. Search for Extraterrestrial Life using Chiral Molecules: Mandelate Racemase as a Test Case. [Internet] [Doctoral dissertation]. Georgia Tech; 2007. [cited 2020 Nov 27].
Available from: http://hdl.handle.net/1853/14527.
Council of Science Editors:
Thaler TL. Search for Extraterrestrial Life using Chiral Molecules: Mandelate Racemase as a Test Case. [Doctoral Dissertation]. Georgia Tech; 2007. Available from: http://hdl.handle.net/1853/14527