Possible salt bridges between transmembrane alpha-helices of the lactose carrier of Escherichia coli
| ISSN: | 0021-9258 |
|---|---|
| DOI: | 10.1016/s0021-9258(19)36751-1 |
| Přístupová URL adresa: | https://explore.openaire.eu/search/publication?articleId=doi_________::d6dea516c75d90f2e578d16791ae344b https://doi.org/10.1016/s0021-9258(19)36751-1 |
| Rights: | OPEN |
| Přírůstkové číslo: | edsair.doi...........d6dea516c75d90f2e578d16791ae344b |
| Autor: | C. Hansen, Pung Pung Hwang, Jong-In Lee, T H Wilson |
| Rok vydání: | 1992 |
| Předmět: | |
| Zdroj: | Journal of Biological Chemistry. 267:20758-20764 |
| ISSN: | 0021-9258 |
| DOI: | 10.1016/s0021-9258(19)36751-1 |
| Popis: | 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. |
| Databáze: | OpenAIRE |
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