tailieunhanh - Báo cáo khoa học: Disorder–order transition of k CII promoted by low concentrations of guanidine hydrochloride suggests a stable core and a flexible C-terminus

The CII protein of bacteriophagek, which activates the synthesis of thekrepressor, plays a key role in the lysis– lysogeny switch. CII has a small in vivo half-life due to its proteolytic susceptibility, and this instability is a key com-ponent for its regulatory role. The structural basis of this instability is not known. While studying guanidine hydro-chloride-assisted unfolding of CII, we found that low concentrations of the chaotrope (50–500 mM) have a con-siderable effect on the structure of this protein. This effect is manifest in an increase in molar ellipticity, an enhancement of intrinsic tryptophanfluorescence intensityandareduction in ANS binding. . | Eur. J. Biochem. 270 4439-4446 2003 FEBS 2003 doi Disorder-order transition of k CII promoted by low concentrations of guanidine hydrochloride suggests a stable core and a flexible C-terminus Ajit B. Datta1 Siddhartha Roy2 and Pradeep Parrack1 1 Department of Biochemistry and 2Department of Biophysics Bose Institute Centenary Campus CIT Scheme VII M India The CII protein of bacteriophage k which activates the synthesis of the k repressor plays a key role in the lysislysogeny switch. CII has a small in vivo half-life due to its proteolytic susceptibility and this instability is a key component for its regulatory role. The structural basis of this instability is not known. While studying guanidine hydro-chloride-assisted unfolding of CII we found that low concentrations of the chaotrope 50-500 mM have a considerable effect on the structure of this protein. This effect is manifest in an increase in molar ellipticity an enhancement of intrinsic tryptophan fluorescence intensity and a reduction in ANS binding. At low concentrations of guanidine hydrochloride CII is stabilized as reflected in a significant decrease in the rate of proteolysis by trypsin and resistance to thermal aggregation while the tetrameric nature of the protein is retained. Thus low concentrations of guanidine hydrochloride promote a more structured conformation of the CII protein. On the basis of these observations a model has been proposed for the structure of CII wherein the protein equilibrates between a compact form and a proteo-lytically accessible form in which the C-terminal region assumes different structures. Keywords bacteriophage k HflB protein proteolysis genetic switch lysogeny. The transcriptional activator protein CII is a key element in the decision that governs the switching of k phage development into one of its two alternate pathways namely lytic or lysogenic 1 2 . A small protein of 97 amino acids CII exists as a tetramer in the native state 3 . .

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