Thermodynamic stability of psychrophilic and mesophilic pheromones of the protozoan ciliate euplotes.
Three psychrophilic protein pheromones (En-1, En-2 and En-6) from the polar ciliate, Euplotes nobilii, and six mesophilic pheromones (Er-1, Er-2, Er-10, Er-11, Er-22 and Er-23) from the temperate-water sister species, Euplotes raikovi, were studied in aqueous solution for their thermal unfolding and refolding based on the temperature dependence of their circular dichroism (CD) spectra. The three psychrophilic proteins showed thermal unfolding with mid points in the temperature range 55-70 °C. In contrast, no unfolding was observed for any of the six mesophilic proteins and their regular secondary structures were maintained up to 95 °C. Possible causes of these differences are discussed based on comparisons of the NMR structures of the nine proteins.
Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037, USA. mgeralt@scripps.edu.
Michael
M
Geralt
Department of Environmental and Natural Sciences, University of Camerino, Camerino 62032, Italy. claudio.alimenti@unicam.it.
Claudio
C
Alimenti
Department of Environmental and Natural Sciences, University of Camerino, Camerino 62032, Italy. adriana.vallesi@unicam.it.
Adriana
A
Vallesi
Department of Environmental and Natural Sciences, University of Camerino, Camerino 62032, Italy. piero.luporini@unicam.it.
Pierangelo
P
Luporini
Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037, USA. wuthrich@mol.biol.ethz.ch.
Kurt
K
Wüthrich