title: Disorder-order transition of lambda CII promoted by low concentrations of guanidine hydrochloride suggests a stable core and a flexible C-terminus.
abstract: The CII protein of bacteriophage lambda, which activates the synthesis of the lambda repressor, 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 component for its regulatory role. The structural basis of this instability is not known. While studying guanidine hydrochloride-assisted unfolding of CII, we found that low concentrations of the chaotrope (50-500 microM) 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 proteolytically accessible form, in which the C-terminal region assumes different structures.
authors: Department of Biochemistry Department of Biophysics, Bose Institute, Centenary Campus, CIT Scheme VII(M), India.
authors: Ajit B
authors: AB
authors: Datta
authors: Siddhartha
authors: S
authors: Roy
authors: Pradeep
authors: P
authors: Parrack
mesh_terms: D000595:Amino Acid Sequence; D002850:Chromatography, Gel; D002942:Circular Dichroism; D019791:Guanidine / Q000494:pharmacology*; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D009994:Osmolar Concentration; D011487:Protein Conformation / Q000187:drug effects; D011489:Protein Denaturation / Q000187:drug effects*; D017510:Protein Folding; D021122:Protein Subunits; D013050:Spectrometry, Fluorescence; D013696:Temperature; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism*; D014357:Trypsin / Q000378:metabolism; D014764:Viral Proteins
chemical_list: D021122:Protein Subunits; D014157:Transcription Factors; D014764:Viral Proteins; C039000:cII protein, bacteriophage lambda; D014357:Trypsin; D019791:Guanidine