Kinetic partitioning. Poising SecB to favor association with a rapidly folding ligand.
Journal - The Journal of biological chemistry (UNITED STATES )
Chaperones are a class of proteins that possess the remarkable ability to selectively bind polypeptides that are in a nonnative state. The selectivity of SecB, a molecular chaperone in Escherichia coli, for its ligands can be explained in part by a kinetic partitioning between folding of the polypeptide and association with SecB. It has clearly been established that kinetic partitioning can be poised to favor association with SecB by changing the rate constant for folding of the ligand. We now demonstrate that binding to SecB can be given a kinetic advantage over the pathway for folding by modulating the properties of the chaperone. By poising SecB to expose a hydrophobic patch, we were able to detect a complex between SecB and maltose-binding protein under conditions in which rapid folding of the polypeptide otherwise precludes formation of a kinetically stable complex. The data presented here are interpreted within the framework of a kinetic partitioning between binding to SecB and folding of the polypeptide. We propose that exposure of a hydrophobic patch on SecB increases the surface area for binding and thereby increases the rate constant for association. In this way association of SecB with the polypeptide ligand has a kinetic advantage over the pathway for folding.
|ISSN : ||0021-9258|
|Mesh Heading : ||Bacterial Proteins Binding Sites Carrier Proteins Kinetics Ligands Peptides Protein Folding Temperature metabolism metabolism|
|Mesh Heading Relevant : ||ATP-Binding Cassette Transporters Escherichia coli Proteins Monosaccharide Transport Proteins metabolism|
Interaction of SecB with intermediates along the folding pathway of maltose-binding protein.
Journal - Protein science : a publication of the Protein Society (UNITED STATES )
SecB, a molecular chaperone involved in protein export in Escherichia coli, displays the remarkable ability to selectively bind many different polypeptide ligands whose only common feature is that of being nonnative. The selectivity is explained in part by a kinetic partitioning between the folding of a polypeptide and its association with SecB. SecB has no affinity for native, stably folded polypeptides but interacts tightly with polypeptides that are nonnative. In order to better understand the nature of the binding, we have examined the interaction of SecB with intermediates along the folding pathway of maltose-binding protein. Taking advantage of forms of maltose-binding protein that are altered in their folding properties, we show that the first intermediate in folding, represented by the collapsed state, binds to SecB, and that the polypeptide remains active as a ligand until it crosses the final energy barrier to attain the native state.
|ISSN : ||0961-8368|
|Mesh Heading : ||Bacterial Proteins Carrier Proteins Dose-Response Relationship, Drug Escherichia coli Guanidine Guanidines Kinetics Molecular Chaperones Mutation Protein Conformation Protein Denaturation chemistry genetics metabolism pharmacology|
|Mesh Heading Relevant : ||ATP-Binding Cassette Transporters Escherichia coli Proteins Monosaccharide Transport Proteins Protein Folding metabolism metabolism metabolism|