The characterization of Csp (Cold Shock Protein) from the Antarctic archaeon, Methanogenium frigidum

Abstract

Cold shock proteins (Csp) are small acidic proteins that fold into β-barrel structures with five anti-parallel β-strands and are involved in essential cellular processes. Upon temperature downshift the synthesis of Csp proteins is drastically increased to enable cells to restore growth in the cold. These proteins facilitate transcription and translation at low temperature by functioning as RNA chaperones. Csp proteins have been most extensively studied in Bacteria but very few Csp homologues have been identified and studied in Archaea. This is the first study examining structural, functional and biophysical properties of Csp from the Antarctic archaeon Methanogenium frigidum. The fastidious growth requirements of M. frigidum make it difficult to cultivate, therefore recombinant methods have been developed for the expression and characterization of the protein. The analysis by transverse urea gradient gel electrophoresis (TUG-GE) revealed that M. frigidum Csp folds by a reversible two-state mechanism and has a low conformational stability. The spectroscopic analysis of the protein performed by Circular Dichroism (CD) spectroscopy disclosed features typical of other homologous proteins. A possible association between Csp and RNA has been proposed according to MALDI-TOF mass spectrometry analysis. The effect of a Nterminal polyhistidine affinity tag on the biophysical properties of Csp was also examined. The biological activity of Csp was investigated by complementation of an E. coli cold sensitive mutant. These studies revealed that the M. frigidum Csp is biologically active and can function in E. coli.