Bechtluft, P, Kedrov, A, Slotboom, DJ, Nouwen, N, Tans, SJ and Driessen, AJ (2010) Tight hydrophobic contacts with the SecB chaperone prevent folding of substrate proteins. Biochemistry 49:2380-8
The molecular chaperone SecB binds to hydrophobic sections of unfolded secretory proteins and thereby prevents their premature folding prior to secretion by the translocase of Escherichia coli. Here, we have investigated the effect of the single-residue mutation of leucine 42 to arginine (L42R) centrally positioned in the polypeptide binding pocket of SecB on its chaperonin function. The mutant retains its tetrameric structure and SecA targeting function but is defective in its holdase activity. Isothermal titration calorimetry and single-molecule optical tweezer studies suggest that the SecB(L42R) mutant exhibits a reduced polypeptide binding affinity allowing for partial folding of the bound polypeptide chain rendering it translocation-incompetent.
Adenosine Triphosphatases/chemistry; Adenosine Triphosphatases/metabolism; Amino Acid Substitution; Bacterial Outer Membrane Proteins/metabolism; Bacterial Proteins/chemistry; Bacterial Proteins/genetics; Bacterial Proteins/metabolism; Escherichia coli; Escherichia coli Proteins/metabolism; Hydrophobic and Hydrophilic Interactions; Maltose-Binding Proteins; Membrane Transport Proteins/chemistry; Membrane Transport Proteins/metabolism; Models, Molecular; Molecular Chaperones/chemistry; Molecular Chaperones/genetics; Molecular Chaperones/metabolism; Mutation; Peptides/metabolism; Periplasmic Binding Proteins/metabolism; Protein Folding; Protein Precursors/metabolism; Protein Structure, Quaternary; Protein Transport
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