Pressure-induced conformational changes in a human Bence-Jones protein (Mcg).
The effect of high static pressures on the internal structure of the immunoglobulin light chain (Bence-Jones) dimer from the patient Mcg was assessed with measurements of intrinsic protein fluorescence polarization and intensity. Depolarization of intrinsic fluorescence was observed at relatively low pressures (less than 2 kbar), with a standard volume change of -93 mL/mol. The significant conformational changes indicated by these observations were not attributable to major protein unfolding, since pressures exceeding 2 kbar were required to alter intrinsic fluorescence emission maxima and yields. Fluorescence intensity and polarization measurements were used to investigate pressure effects on the binding of bis(8-anilino-naphthalene-1-sulfonate) (bis-ANS), rhodamine 123, and bis(N-methylacridinium nitrate) (lucigenin). Below 1.5 kbar the Mcg dimer exhibited a small decrease in affinity for bis-ANS (standard volume change approximately 5.9 mL/mol). At 3 kbar the binding activity increased by greater than 250-fold (volume change -144 mL/mol) and remained 10-fold higher than its starting value after decompression. With rhodamine 123 the binding activity showed an initial linear increase but plateaued at pressures greater than 1.5 kbar (standard volume change -23 mL/mol). These pressure effects were completely reversible. Binding activity with lucigenin increased slightly at low pressures (standard volume change -5.5 mL/mol), but the protein was partially denatured at pressures greater than 2 kbar. Taken in concert with the results of parallel binding studies in crystals of the Mcg dimer, these observations support the concept of a large malleable binding region with broad specificity for aromatic compounds.(ABSTRACT TRUNCATED AT 250 WORDS)
D000166:Acridines; D000686:Amyloidosis / Q000652:urine; D000817:Anilino Naphthalenesulfonates; D001536:Bence Jones Protein / Q000378:metabolism*; D005456:Fluorescent Dyes; D006801:Humans; D007700:Kinetics; D011312:Pressure; D011487:Protein Conformation; D020112:Rhodamine 123; D012235:Rhodamines; D013050:Spectrometry, Fluorescence
D000166:Acridines; D000817:Anilino Naphthalenesulfonates; D005456:Fluorescent Dyes; D012235:Rhodamines; D020112:Rhodamine 123; C033472:10,10'-dimethyl-9,9'-biacridinium; C027132:1-anilino-8-naphthalenesulfonate; D001536:Bence Jones Protein