PMID:7654173
| Citation |
Black, PN and Zhang, Q (1995) Evidence that His110 of the protein FadL in the outer membrane of Escherichia coli is involved in the binding and uptake of long-chain fatty acids: possible role of this residue in carboxylate binding. Biochem. J. 310 ( Pt 2):389-94 |
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| Abstract |
The binding of exogenous fatty acids to the outer-membrane protein FadL of Escherichia coli is specific for long-chain fatty acids (C14-C18). Oleoyl alcohol [(Z)-9-octadecen-1-ol] and methyl oleate were unable to displace FadL-specific binding of [3H]oleate (C18:1), suggesting that the carboxylate of the long-chain fatty acid was required for binding. Therefore the binding of exogenous fatty acids to FadL is governed, in part, by the carboxy group of the long-chain fatty acid. Treatment of whole cells with 1 mM diethyl pyrocarbonate (DEPC) depressed binding by 43-73% over the range of oleate concentrations used (10-500 nM). On the basis of these results and the notion that histidine residues often play a role involving proton transfer and charge-pairing, the five histidine residues within FadL (His110, His226, His327, His345 and His418) were replaced by alanine using site-directed mutagenesis. Altered FadL proteins were correctly localized in the outer membrane at wild-type levels and retained the heat-modifiable property characteristic of the wild-type protein. Initial screening of these fadL mutants revealed that the replacement of His110 by Ala resulted in a decreased growth rate on minimal oleate/agar plates. The rates of long-chain fatty acid transport for delta fadL strains harbouring each mutation on a plasmid, with the exception of fadLH110A, were the same, or nearly the same, as those for the wild-type. fadLH110A was also defective in binding, arguing that the functional effect of this mutation was at the level of long-chain-fatty-acid binding.(ABSTRACT TRUNCATED AT 250 WORDS) |
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| Keywords |
Alanine; Amino Acid Sequence; Bacterial Outer Membrane Proteins/chemistry; Bacterial Outer Membrane Proteins/drug effects; Bacterial Outer Membrane Proteins/metabolism; Base Sequence; Binding Sites; Binding, Competitive; Biological Transport; Diethyl Pyrocarbonate/pharmacology; Escherichia coli/genetics; Escherichia coli/metabolism; Escherichia coli Proteins; Fatty Acid Transport Proteins; Genes, Bacterial; Histidine; Kinetics; Molecular Sequence Data; Mutagenesis, Site-Directed; Oleic Acid; Oleic Acids/metabolism; Oligodeoxyribonucleotides; Plasmids; Point Mutation; Recombinant Proteins/chemistry; Recombinant Proteins/drug effects; Recombinant Proteins/metabolism |
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