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A topological model for the high‐affinity nickel transporter of Alcaligenes eutrophus
Author(s) -
Eitinger Thomas,
Friedrich Bärbel
Publication year - 1994
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.1994.tb01090.x
Subject(s) - biology , transporter , alcaligenes , nickel , computational biology , gene , genetics , bacteria , materials science , metallurgy , pseudomonas
Summary The gene hoxN of Alcaligenes eutrophus encodes a membrane protein with a molecular mass of 33.1 kDa that mediates energy‐dependent uptake of nickel ions. Based on the hydrophobicity of the HoxN protein five, six, or seven transmembrane segments were predicted, depending on the algorithm used for computer analysis. To distinguish between these possibilities varying segments of the amino‐terminal end of the transporter were fused to the Escherichia coli enzymes aikaline phosphatase (PhoA) or β‐galactosidase (LacZ). The enzymatic activity of 16 HoxN‐PhoA and 15 HoxN‐LacZ fusions was determined. On the assumption that PhoA fusions only exhibit high activity when fused to periplasmic domains of the target, while LacZ fusions are only active when oriented towards the cytoplasm, a two‐dimensional model for the nickel transporter was developed. This model proposes that HoxN contains four periplasmic and four cytoplasmic regions, and seven transmembrane helices. The amino terminus is located in the cytoplasm, and the carboxyl terminus faces the periplasm.