title: Mutational alterations affecting the export competence of a truncated but fully functional maltose-binding protein signal peptide.
abstract: The wild-type maltose-binding protein (MBP) signal peptide is 26 amino acids in length. A mutationally altered MBP signal peptide has been previously described that is missing one of the basic residues from the hydrophilic segment and seven residues from the hydrophobic core; however, it still facilitates MBP secretion to the periplasm at a rate and efficiency comparable to those of the wild-type structure. Thus, this truncated signal peptide (designated the R2 signal peptide) must retain all of the essential features required for proper export function. In this study, alterations were obtained in the R2 signal peptide that resulted in an export-defective MBP. For the first time, signal sequence mutations were obtained that resulted in the synthesis of a totally export-defective MBP. As was previously the case for the wild-type signal peptide, the introduction of either charged residues or helix-breaking proline residues adversely affected export function. Despite these similarities, the position of these alterations within the R2 signal peptide, their relative effects on MBP secretion and processing, and an analysis of the ability of various extragenic prl mutations to suppress the secretion defects provide additional insight into the minimal requirements for a functional MBP signal peptide.
authors.forename: J D
authors.initials: JD
authors.lastname: Fikes
authors.forename: V A
authors.initials: VA
authors.lastname: Bankaitis
authors.forename: J P
authors.initials: JP
authors.lastname: Ryan
authors.forename: P J
authors.initials: PJ
authors.lastname: Bassford
mesh_terms: D018528:ATP-Binding Cassette Transporters; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000502:physiology; D001483:Base Sequence; D001692:Biological Transport; D002352:Carrier Proteins / Q000502:physiology*; D002451:Cell Compartmentation; D004926:Escherichia coli; D029968:Escherichia coli Proteins; D008320:Maltose / Q000378:metabolism*; D058619:Maltose-Binding Proteins; D008565:Membrane Proteins / Q000502:physiology*; D009004:Monosaccharide Transport Proteins; D009154:Mutation; D011499:Protein Processing, Post-Translational; D021382:Protein Sorting Signals / Q000502:physiology*; D013329:Structure-Activity Relationship; D013489:Suppression, Genetic
chemical_list: D018528:ATP-Binding Cassette Transporters; D001426:Bacterial Proteins; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; D058619:Maltose-Binding Proteins; D008565:Membrane Proteins; D009004:Monosaccharide Transport Proteins; D021382:Protein Sorting Signals; C461599:maltose transport system, E coli; D008320:Maltose