Identification of 'molten globule'-like state in all beta-sheet protein.
The cardiotoxin analogue III (CTX III), isolated from the Taiwan Cobra venom (Naja naja atra), is a sixty amino acid, all beta-sheet protein. The 2,2,2-trifluoro ethanol (TFE) induced unfolding of CTX III is studied under acidic conditions (pH 2.5). Using circular dichroism, 1-anilino-8-napthalene sulphonic acid binding and NMR experiments, it is shown that stable, partially structured state(s) ['molten globule'-like state] is formed between 50 and 80% TFE concentrations. The protein was found to exist in an unfolded state in 80% TFE containing 2M urea. The TFE induced unfolding process is shown to be completely reversible. In the 'molten globule' state of CTX III in 80% TFE, though portion(s) of the backbone of the protein assume helical conformation, most of the original beta-sheet secondary structural elements in the protein are intact. In our opinion, this is the first report of the identification of a 'molten globule'-like state in the unfolding pathway of an all beta-sheet monomeric protein.
Kumar
T K
TK
Chemistry Department, National Tsing Hua University, Hsinchu, Taiwan.
Jayaraman
G
G
Lee
C S
CS
Sivaraman
T
T
Lin
W Y
WY
Yu
C
C
D000817:Anilino Naphthalenesulfonates; D002942:Circular Dichroism; D004179:Cobra Cardiotoxin Proteins / Q000737:chemistry* / Q000302:isolation & purification; D004546:Elapid Venoms; D005456:Fluorescent Dyes; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D017510:Protein Folding; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence
D000817:Anilino Naphthalenesulfonates; D004179:Cobra Cardiotoxin Proteins; D004546:Elapid Venoms; D005456:Fluorescent Dyes; C082202:cardiotoxin III, Naja naja atra; C027132:1-anilino-8-naphthalenesulfonate