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Thermal Stability and Structure Analysis of the E2 component of the Bacillus
stearothermophilus Pyruvate Dehydrogenase Complex
Cesar Ruiz
Mentor: Dr. Szu-Wen Wang
The E2 component of the Bacillus stearothermophilus pyruvate dehydrogenase complex
can potentially be used as a scaffold to create a targeted drug delivery system. It is
capable of assembling into a 60-mer unit dodecahedron with icosahedral symmetry, even
with the addition of peptides on the surface. Circular dichroism (CD) and differential
scanning calorimetry (DSC) were used to determine the thermostability of the E2
complex. This protein scaffold has been shown to be stable at temperatures up to ~80 ºC.
When subjected to ~80 ºC incubation, precipitation was observed, indicating that the
thermal unfolding of the protein was irreversible. The dependence on scan rate and
concentration of the DSC scans indicates that the unfolding process is kinetically
controlled. Secondary structure analysis with CD and K2D software estimates that E2 is
composed of ~41-45% α-helix and ~18-23% β-sheet, which compares well with
crystallographic data. A thermal transition scan with CD shows that the melting
temperature, TM, is 83 ºC, which is consistent with the DSC data. Mutagenesis on E2 was
done, and thermal scans show that these mutants are also stable at high temperatures. The
high thermal stability exhibited by the wild type and mutant protein assemblies suggests
that this protein would be a good scaffold for molecular encapsulation in drug delivery.