Structure and function of phosphoglucose isomerase in Colias eurytheme
Abstract/Contents
- Abstract
- Butterflies belonging to the genus Colias are widespread throughout North America and populations are found in a diversity of habitats from lowland valleys to alpine grasslands and tundra. The thermal ecology of these habitats results in selective pressure on the metabolic enzymes in Colias to maximize flight performance, a key component of fitness for butterflies. Strong balancing selection on the glycolytic enzyme phosphoglucose isomerase (PGI) has produced persistent polymorphisms in many species. The evolutionary impacts of this polymorphism have been well studied and both heterozygote advantage for PGI and homozygote tradeoff of Vmax/Km versus thermals stability are known to be driving the balancing selection. This first study reported in the first chapter investigated the relationship between the structural polymorphisms of the PGI enzyme and the functional consequences that determine fitness. I pursued this by first reporting the native structure of PGI from Colias eurytheme as determined by x-ray crystallography. I then assayed the kcat / Km and thermal stability of three different homodimers of C. eurytheme PGI to demonstrate the tradeoff between the two functional characteristics in homodimers. Following this I used molecular dynamics simulations to investigate properties of the three homodimers that may be contributing to the observed functional differences. Those properties were hydrogen bonding patterns of the polymorphic sites, overall backbone movement, and distance between the catalytic residues. All three properties varied with with thermal stability and kcat / Km. The second set of experiments concerned the fixed difference at codon 370 between C. meadii and C. eurytheme. This fixed difference corresponded to the invasion of lowland habitats and is known to confer thermal stability to PGI. The evolutionary path of codon 370 from the ancestral glycine found in C. meadii and the derived serine found in C. euytheme would have required two mutations that would have produce either alanine or tryptophan as intermediate states. I expressed and assayed four homodimers that differ only at codon 370 and show that the mutation from glycine to serine exchanges kcat / Km for thermal stability as predicted. The putative intermediate alanine is similar to glycine, and the putative intermediate tryptophan has both poor kinetics and poor thermal stability. The results demonstrate that a single site change can make a large difference in modulating the tradeoff in homozygotes between kcat / Km and thermal stability and that the most likely evolutionary path was Gly → Ala → Ser at codon 370. Finally general results of the molecular dynamics approach are presented that reveal the stochastic nature of hydrogen bonding around polymorphic sites. A general trend between backbone carbon movement and charge-variant of the PGI dimer is also found.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2013 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Hill, Jason Anthony |
|---|---|
| Associated with | Stanford University, Department of Biology. |
| Primary advisor | Watt, Ward B |
| Thesis advisor | Watt, Ward B |
| Thesis advisor | Jardetzky, Theodore |
| Thesis advisor | Tuljapurkar, Shripad, 1951- |
| Advisor | Jardetzky, Theodore |
| Advisor | Tuljapurkar, Shripad, 1951- |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Jason Anthony Hill. |
|---|---|
| Note | Submitted to the Department of Biology. |
| Thesis | Ph.D. Stanford University 2013 |
| Location | electronic resource |
Access conditions
- Copyright
- © 2013 by Jason Anthony Hill
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
Also listed in
Loading usage metrics...