Molten globule state of equine beta-lactoglobulin.
The acid-unfolded state of equine beta-lactoglobulin was characterized by means of circular dichroism, nuclear magnetic resonance, analytical gel-filtration chromatography, and analytical centrifugation. The acid-unfolded state of equine beta-lactoglobulin has a substantial secondary structure as shown by the far-ultraviolet circular dichroism spectrum but lacks persistent tertiary packing of the side chains as indicated by the near-ultraviolet circular dichroism and nuclear magnetic resonance spectra. It is nearly as compact as the native conformation as shown by the gel filtration and sedimentation experiments, and it has the exposed hydrophobic surface as indicated by its tendency to aggregate. All of these characteristics indicate that the acid-unfolded state of equine beta-lactoglobulin is a molten globule state. The alpha helix content in the acid-unfolded state, which has been estimated from the circular dichroism spectrum, is larger than that in the native state, suggesting the presence of nonnative alpha helices in the molten globule state. This result suggests the generality of the intermediate with nonnative alpha helices during the folding of proteins having the beta-clam fold.
Ikeguchi
M
M
Department of Bioengineering, Faculty of Engineering, Soka University, Tokyo, Japan.
Kato
S
S
Shimizu
A
A
Sugai
S
S
D000143:Acids; D000595:Amino Acid Sequence; D000818:Animals; D002850:Chromatography, Gel; D002942:Circular Dichroism; D006736:Horses; D006863:Hydrogen-Ion Concentration; D007782:Lactoglobulins / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D010316:Particle Size; D017510:Protein Folding; D017433:Protein Structure, Secondary; D012177:Retinol-Binding Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D014461:Ultracentrifugation
D000143:Acids; D007782:Lactoglobulins; D012177:Retinol-Binding Proteins