Misfolded Protein - a Cellular Indicator for the Expression of Heat Shock Proteins
Goh, Jo Wern
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After exposure to stressful conditions, cells increase expression of heat shock proteins, a set of proteins that have been implicated in the protection of protein structure and function. A common consequence of the stresses that induce the heat shock response may be the unfolding of proteins. Therefore, the expression of heat shock proteins may be induced by the presence of misfolded proteins. The present experiment examined the role of misfolded proteins in the induction of heat shock response in Nicotiana tabacum L. var. Petit Havana transformed with the rubisco large and small subunit genes from the diatom Phaeodactylum tricornutum. The foreign algal rubisco subunits are highly expressed but fail to fold and assemble properly into functional holoenzyme in the tobacco chloroplast. Content of heat shock proteins was assessed by immunoblotting of the mature leaf tissue extracts, from both the supernatant and pellet fractions. The content of Hsp60 was much greater in the transgenic plants (and heat-shocked plants) than in the non-transformed control plants; immunoreactivity was confined to the supernatant fraction. An increase in soluble Hsp93 was also observed in the transgenic plants relative to the controls. Although heat shock substantially increased the levels of small Hsps and Hsp101, these proteins were not detected in the transgenic plants. There were no noticeable differences in the soluble content of cytoplasmic Hsp70 and stromal Hsp70 between the transgenic and control plants. Subsequent 2-D Western analysis detected the presence of Hsp70 isoforms in the transgenic plants but did not resolve its induction level relative to the controls. Taken together, these results provide support for the hypothesis that the presence of misfolded proteins induces the production of heat shock proteins; however the response is restricted to certain classes of heat shock proteins.
Franklin and Marshall College Archives, Undergraduate Honors Thesis 2005
- F&M Theses Collection