Cloning, purification and characterization of a 90kDa heat shock protein from Citrus sinensis (sweet orange).

Protein misfolding is stimulated by stress, such as heat, and heat shock proteins (Hsps) are the first line of defense against these undesirable situations. Plants, which are naturally sessile, are perhaps more exposed to stress factors than some other organisms, and consequently, the role of Hsps is crucial to maintain homeostasis. Hsp90, because of its key role in infection and other stresses, is targeted in therapies that improve plant production by increasing resistance to both biotic and abiotic stress. In addition, Hsp90 is a primary factor in the maintenance of homeostasis in plants. Therefore, we cloned and purified Hsp90 from Citrus sinensis (sweet orange). Recombinant C. sinensis Hsp90 (rCsHsp90) was produced and measured by circular dichroism (CD), intrinsic fluorescence spectroscopy and dynamic light scattering. rCsHsp90 formed a dimer in solution with a Stokes radius of approximately 62Å. In addition, it was resistant to thermal unfolding, was able to protect citrate synthase from aggregation, and Western blot analysis demonstrated that CsHsp90 was constitutively expressed in C. sinensis cells. Our analysis indicated that CsHsp90 is conformationally similar to that of yeast Hsp90, for which structural information is available. Therefore, we showed that C. sinensis expresses an Hsp90 chaperone that has a conformation and function similar to other Hsp90s.