title: Mutations of the molecular chaperone protein SecB which alter the interaction between SecB and maltose-binding protein.
abstract: SecB is a 16-kDa cytosolic chaperone protein that is required for efficient export of particular proteins in Escherichia coli. To identify regions of SecB that contribute to efficient protein export, we isolated secB point mutants that are defective for protein export in vivo. We obtained missense mutations at residues Leu75 (SecBL75Q), Cys76 (SecBC76Y), and Glu77 (SecBE77K) in the center of the secB gene. In vivo, mutant SecBL75Q and SecBE77K proteins are capable of binding to precursor maltose-binding protein (MBP) and preventing the formation of export-incompetent precursor MBP; however, export of MBP is still defective. In vitro, purified SecBL75Q and SecBE77K proteins bound to unfolded MBP and blocked its refolding. SecBL75Q and SecBE77K were more effective than wild-type SecB at blocking the refolding of unfolded MBP, suggesting that SecBL75Q and SecBE77K have a higher affinity for unfolded MBP.
authors.affiliation: Department of Physiology, Tufts University School of Medicine, Boston, Massachusetts 02111.
authors.forename: P M
authors.initials: PM
authors.lastname: Gannon
authors.forename: C A
authors.initials: CA
authors.lastname: Kumamoto
mesh_terms: D018528:ATP-Binding Cassette Transporters; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D004926:Escherichia coli / Q000737:chemistry / Q000235:genetics; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial; D058619:Maltose-Binding Proteins; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins; D009154:Mutation; D017510:Protein Folding; D011498:Protein Precursors / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D058619:Maltose-Binding Proteins; D009004:Monosaccharide Transport Proteins; D011498:Protein Precursors; C057842:SecB protein, Bacteria; C461599:maltose transport system, E coli; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone