Possible salt bridges between transmembrane alpha-helices of the lactose carrier of Escherichia coli.
In: The Journal of biological chemistry, Jg. 267 (1992-10-15), Heft 29, S. 20758
academicJournal
Zugriff:
Although it is energetically extremely unfavorable to have charged amino acid residues of a polypeptide in the hydrophobic environment of the membrane phospholipid bilayer, a few such charged residues are found in membrane-spanning regions of membrane proteins. Ion pairs (salt bridges) would be much more stable in low dielectric media than single ionized residues. This paper provides indirect evidence for a salt bridge between Asp-240 and Lys-319 in the lactose carrier of Escherichia coli. When Asp-240 was changed to alanine by site-directed mutagenesis, there was a loss of the ability to accumulate methyl-beta-D-thiogalactopyranoside (TMG), melibiose, or lactose. Fast-growing revertants were isolated on melibiose minimal agar plates. Two second-site revertants were isolated: Asp-240-->Ala plus Gly-268-->Val and Asp-240-->Ala plus Lys-319-->Gln. These revertants showed extremely poor accumulation of TMG, melibiose, and lactose, but showed significant "downhill" lactose entry into beta-galactosidase-containing cells with sugar concentrations of 2 and 5 mM. It is concluded that there is some important interaction between Asp-240 and Lys-319, possibly a salt bridge.
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Possible salt bridges between transmembrane alpha-helices of the lactose carrier of Escherichia coli.
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Autor/in / Beteiligte Person: | Lee, JI ; Hwang, PP ; Hansen, C ; Wilson, TH |
Zeitschrift: | The Journal of biological chemistry, Jg. 267 (1992-10-15), Heft 29, S. 20758 |
Veröffentlichung: | 2021- : [New York, NY] : Elsevier Inc. on behalf of American Society for Biochemistry and Molecular Biology ; <i>Original Publication</i>: Baltimore, MD : American Society for Biochemistry and Molecular Biology, 1992 |
Medientyp: | academicJournal |
ISSN: | 0021-9258 (print) |
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