Adenylate kinase from Sulfolobus acidocaldarius: Expression in Escherichia coli and characterization by Fourier transform infrared spectroscopy

Adenylate kinase from the extremely thermoacidophilic archaeon Sulfolobus acidocaldarius has been overexpressed in Escherichia coli. The highly purified enzyme was characterized by Fourier transform infrared spectroscopy (FTIR). Analysis of FTIR spectra and estimation of secondary structure revealed a global protein structure similar to that of other adenylate kinases. Thermal unfolding of the protein with an estimated T-m value near 90 degrees C is irreversible due to protein aggregation. The enzyme exhibits long-term stability up to 80 degrees C, which is an excellent adaptation to the physiological growth temperature of 75-80 degrees C. Halfwidths of secondary-structure-sensitive bands and hydrogen-deuterium exchange experiments revealed that in comparison to adenylate kinase from porcine muscle cytosol the Sulfolobus enzyme is characterized by a significantly more compact and rigid protein core structure, which is likely to contribute specifically to the extreme thermostability of the protein. (C) 1996 Academic Press, Inc.