SecB binds only to a late native-like intermediate in the folding pathway of barstar and not to the unfolded state.
SecB is a cytosolic, tetrameric chaperone of Escherichia coli which maintains precursor proteins in a translocation competent state. We have investigated the effect of SecB on the refolding kinetics of the small protein barstar in 1 M guanidine hydrochloride at pH 7.0 and 25 degreesC using fluorescence spectroscopy. We show that SecB does not bind either the native or the unfolded states of barstar but binds to a late near-native intermediate along the folding pathway. For barstar, polypeptide collapse and formation of a hydrophobic surface are required for binding to SecB. SecB does not change the apparent rate constant of barstar refolding. The kinetic data for SecB binding to barstar are not consistent with simple kinetic partitioning models.
Molecular Biophysics Unit, Indian Institute of Science, Bangalore.
V G
VG
Panse
J B
JB
Udgaonkar
R
R
Varadarajan
D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism; D004926:Escherichia coli; D019791:Guanidine; D007700:Kinetics; D018832:Molecular Chaperones / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011489:Protein Denaturation; D017510:Protein Folding; D012260:Ribonucleases / Q000037:antagonists & inhibitors; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics
D001426:Bacterial Proteins; D004791:Enzyme Inhibitors; D018832:Molecular Chaperones; C057842:SecB protein, Bacteria; C057438:barstar protein, Bacillus amyloliquefaciens; D012260:Ribonucleases; C019760:Bacillus amyloliquefaciens ribonuclease; D019791:Guanidine