Hexafluoroacetone hydrate as a structure modifier in proteins: characterization of a molten globule state of hen egg-white lysozyme.
A molten globule-like state of hen egg-white lysozyme has been characterized in 25% aqueous hexafluoroacetone hydrate (HFA) by CD, fluorescence, NMR, and H/D exchange experiments. The far UV CD spectra of lysozyme in 25% HFA supports retention of native-like secondary structure while the loss of near UV CD bands are indicative of the overall collapse of the tertiary structure. The intermediate state in 25% HFA exhibits an enhanced affinity towards the hydrophobic dye, ANS, and a native-like tryptophan fluorescence quenching. 1-D NMR spectra indicates loss of native-like tertiary fold as evident from the absence of ring current-shifted 1H resonances. CD, fluorescence, and NMR suggest that the transition from the native state to a molten globule state in 25% HFA is a cooperative process. A second structural transition from this compact molten globule-like state to an "open" helical state is observed at higher concentrations of HFA (> or = 50%). This transition is characterized by a dramatic loss of ANS binding with a concomitant increase in far UV CD bands. The thermal unfolding of the molten globule state in 25% HFA is sharply cooperative, indicating a predominant role of side-chain-side-chain interactions in the stability of the partially folded state. H/D exchange experiments yield higher protection factors for many of the backbone amide protons from the four alpha-helices along with the C-terminal 3(10) helix, whereas little or no protection is observed for most of the amide protons from the triple-stranded antiparallel beta-sheet domain. This equilibrium molten globule-like state of lysozyme in 25% HFA is remarkably similar to the molten globule state observed for alpha-lactalbumin and also with the molten globule state transiently observed in the kinetic refolding experiments of hen lysozyme. These results suggest that HFA may prove generally useful as a structure modifier in proteins.
Bhattacharjya
S
S
Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India.
Balaram
P
P
D000096:Acetone / Q000031:analogs & derivatives; D000818:Animals; D002645:Chickens; D002942:Circular Dichroism; D005260:Female; D005466:Fluorocarbons; D009682:Magnetic Resonance Spectroscopy; D009113:Muramidase / Q000737:chemistry*; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D014364:Tryptophan; D014867:Water; D006845:Hydrocarbons, Fluorinated
D000096:Acetone; D005466:Fluorocarbons; D009113:Muramidase; D014364:Tryptophan; D014867:Water; C017366:hexafluoroacetone; D006845:Hydrocarbons, Fluorinated