Protease from Serratia proteamaculans (PSP) is the first known psychrophilic oligopeptidase B. The gene of S. proteamaculans 94 oligopeptidase B was cloned, sequenced and expressed in Escherichia coli. The unfolding of PSP molecule following heat treatment at 37 degrees C by measuring fluorescence spectra was examined in parallel with the residual activity determination. The effect of PSP thermostabilization by glycerol at 37-50 degrees C was revealed. Calcium ions and buffer solution of low molarity cause the opposite effect - the acceleration of PSP inactivation at 37 degrees C. The thermal stability of PSP molecule in the presence of 0-100 mM CaCl2 was also investigated by means of high-sensitivity differential scanning calorimetry. The artificial reconstruction of the natural complex PSP-chaperonin from S. proteamaculans was carried out: the stable complex (1:1) of chaperonin E. coli GroEL with active recombinant enzyme PSP was obtained. It was shown that complex formation with chaperonin promotes PSP thermostability at 37 degrees C. (C) 2013 Elsevier Inc. All rights reserved.