Chemical Modification of the Bacterial Porin OmpF: Gain of Selectivity by Volume Reduction

• Published in: Biophysical journal Vol. 90; no. 4; pp. 1202 - 1211
• Main Authors: Vrouenraets, Maarten, Wierenga, Jenny, Meijberg, Wim, Miedema, Henk
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.02.2006; Biophysical Society
• Subjects: Amino acids; Amino Acids - chemistry; Bacteria; Channels, Receptors, and Electrical Signaling; Chemicals; Cysteine - genetics; Electrophysiology; Escherichia coli; Escherichia coli - metabolism; Ethyl Methanesulfonate - analogs & derivatives; Ethyl Methanesulfonate - chemistry; Glutathione - chemistry; Ion Channel Gating - physiology; Membranes; Mutation; Peptides - chemistry; Porins - chemistry; Porins - genetics; Porins - physiology; Proteins; Sensitivity and Specificity
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1529/biophysj.105.072298

OmpF is an essentially nonselective porin isolated from the outer membrane of Escherichia coli. Here we report on the manipulation of the ion selectivity of OmpF by chemical modification with MTS reagents (MTSET, MTSEA, and MTSES) and the (rather bulky) tripeptide glutathione, all cysteine specific. When recorded in a gradient of 0.1//1 M CaCl 2 or 0.1//1 M NaCl, pH 7.4 solutions, measured reversal potentials of the most cation-selective modified mutants were (virtually) identical to the Nernst potential of Ca 2+ or Na +. Compared to this full cation selectivity, the anion-selective modified mutants performed somewhat less but nevertheless showed high anion selectivity. We conclude that a low permanent charge in combination with a narrow pore can render the same selectivity as a highly charged but wider pore. These results favor the view that both the electrostatic potential arising form the fixed charge in the pore and the space available at the selectivity filter contribute to the charge selection (i.e., cation versus anion selectivity) of a biological ion channel.