Importance of transmembrane segments in Escherichia coli SecY.
To assess the functional importance of the transmembrane regions of SecY, we constructed a series of SecY variants, in which the six central residues of each transmembrane segment were replaced by amino acid residues from either transmembrane segment 3 or 4 of LacY. The SecY function, as assessed by the ability to complement cold-sensitive secYmutants with respect to their growth and translocase defects, was eliminated by the alterations in transmembrane segments 2, 3, 4, 7, 9 and 10. Among them, those in segments 3 and 4 had especially severe effects. In contrast, transmembrane segments 1, 5, 6, and 8 were more tolerant to the sequence alterations. The purified protein with an altered transmembrane segment 6 retained, in large measure, the ability to support SecA-dependent preprotein translocation in vitro. These results will help us to further understand how the SecYEG protein translocation channel functions.
Shimokawa
N
N
Institute for Virus Research, Kyoto University, Sakyo-ku, Japan.
Mori
H
H
Ito
K
K
D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D019281:Dimerization; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D005816:Genetic Complementation Test; D015151:Immunoblotting; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D000069816:SEC Translocation Channels; D013696:Temperature
D029968:Escherichia coli Proteins; D000069816:SEC Translocation Channels; C057841:SecY protein, E coli