title: Intragenic reversion mutations that improve export of maltose-binding protein in Escherichia coli malE signal sequence mutants.
abstract: Escherichia coli strains harboring malE signal sequence point mutations accumulate export-defective precursor maltose-binding protein (MBP) in the cytoplasm. Beginning with these mutants, a number of spontaneous intragenic revertants have been obtained in which export of the MBP to the periplasm is either partially or totally restored. With a single exception, each of the reversion mutations resulted in an increase in the overall hydrophobicity of the signal peptide hydrophobic core by one of five different mechanisms. In some revertants, MBP export was achieved at a rate comparable to the wild type MBP; in other cases, the rate of MBP export was significantly slower than wild type. The results indicate that the overall hydrophobicity of the signal peptide, rather than the absolute length of its uninterrupted hydrophobic core, is a major determinant of MBP export competency. An alteration at residue 19 of the mature MBP also has been identified that provides fairly efficient suppression of the export defect in the adjacent signal peptide, further suggesting that important export information may reside in this region of the precursor protein.
mesh_terms: D018528:ATP-Binding Cassette Transporters; D000595:Amino Acid Sequence; D001483:Base Sequence; D002352:Carrier Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D007163:Immunosorbent Techniques; D058619:Maltose-Binding Proteins; D009004:Monosaccharide Transport Proteins; D009154:Mutation; D033902:Periplasmic Binding Proteins; D010641:Phenotype; D021382:Protein Sorting Signals / Q000235:genetics*
chemical_list: D018528:ATP-Binding Cassette Transporters; D002352:Carrier Proteins; D029968:Escherichia coli Proteins; C461619:MalE protein, E coli; D058619:Maltose-Binding Proteins; D009004:Monosaccharide Transport Proteins; D033902:Periplasmic Binding Proteins; D021382:Protein Sorting Signals; C461599:maltose transport system, E coli