Gramicidin A analogs: influence of the substitution of the tryptophans by naphthylalanines

Amino acid sequence modulation of gramicidin channel function: effects of tryptophan-to-phenylalanine substitutions on the single-channel conductance and duration

“…The magnitude of the conductance decrease is roughly proportional to the number of Trp -» Phe substitutions. A similar effect was found on the Cs+ permeability of gramicidins in which two or more Trps were replaced by napthylalanines (Daumas et al, 1989).…”

Amino acid sequence modulation of gramicidin channel function: effects of tryptophan-to-phenylalanine substitutions on the single-channel conductance and duration

“…The magnitude of the conductance decrease is roughly proportional to the number of Trp -» Phe substitutions. A similar effect was found on the Cs+ permeability of gramicidins in which two or more Trps were replaced by napthylalanines (Daumas et al, 1989).…”

Gramicidin channels that have no tryptophan residues

“…The increased voltage dependence should vary as a function of the ratio of the dissociation and translocation rate constants [e.g., Andersen (1989)]-the higher the ratio, the steeper the voltage dependence. The present results [and those of Daumas et al (1989Daumas et al ( ,1991] thus suggest that the translocation rate constant is decreased as well; see also Heitz et al (1989). [This conclusion would hold unconditionally if the channels were occupied by at most one ion; but gA channels can be occupied by two Cs+ (Finkelstein & Andersen, 1981), which complicates the analysis.…”

Steered Molecular Dynamics Simulations of Na + Permeation across the Gramicidin A Channel

“…It has been shown that the channel conductance can be modulated by modification of electrical dipole potentials from side chains of Trp, upon either replacement of Trp with a nonpolar amino acid or indole fluorination. [53][54][55][56] The orientation of Trp side chains affects the orientation of the dipole moment and ultimately imposes effects on lowering the overall free energy at the ion-binding site and hence the ion permeation. Table 1 summarizes the dihedral angles of Trp side chains, χ 1 and χ 2 , in the presence and absence of halothane.…”

“…Orientations of Tryptophan Residues. Many lines of experimental evidence indicate that Trp residues are critical to the function of the gA channel. − In addition to their role as anchoring residues at the lipid−water interface to stabilize the channel in the transmembrane orientation, Trp residues at the entrance region of gA are important for ion permeation through noncontact dipole effects. It has been shown that the channel conductance can be modulated by modification of electrical dipole potentials from side chains of Trp, upon either replacement of Trp with a nonpolar amino acid or indole fluorination. − The orientation of Trp side chains affects the orientation of the dipole moment and ultimately imposes effects on lowering the overall free energy at the ion-binding site and hence the ion permeation.…”

“…Many lines of experimental evidence indicate that Trp residues are critical to the function of the gA channel. − In addition to their role as anchoring residues at the lipid−water interface to stabilize the channel in the transmembrane orientation, Trp residues at the entrance region of gA are important for ion permeation through noncontact dipole effects. It has been shown that the channel conductance can be modulated by modification of electrical dipole potentials from side chains of Trp, upon either replacement of Trp with a nonpolar amino acid or indole fluorination. − The orientation of Trp side chains affects the orientation of the dipole moment and ultimately imposes effects on lowering the overall free energy at the ion-binding site and hence the ion permeation. Table summarizes the dihedral angles of Trp side chains, χ 1 and χ 2 , in the presence and absence of halothane.…”

Amino acid sequence modulation of gramicidin channel function: effects of tryptophan-to-phenylalanine substitutions on the single-channel conductance and duration

“…The magnitude of the conductance decrease is roughly proportional to the number of Trp -» Phe substitutions. A similar effect was found on the Cs+ permeability of gramicidins in which two or more Trps were replaced by napthylalanines (Daumas et al, 1989).…”

Gramicidin channels that have no tryptophan residues

“…The increased voltage dependence should vary as a function of the ratio of the dissociation and translocation rate constants [e.g., Andersen (1989)]-the higher the ratio, the steeper the voltage dependence. The present results [and those of Daumas et al (1989Daumas et al ( ,1991] thus suggest that the translocation rate constant is decreased as well; see also Heitz et al (1989). [This conclusion would hold unconditionally if the channels were occupied by at most one ion; but gA channels can be occupied by two Cs+ (Finkelstein & Andersen, 1981), which complicates the analysis.…”

Steered Molecular Dynamics Simulations of Na + Permeation across the Gramicidin A Channel

“…It has been shown that the channel conductance can be modulated by modification of electrical dipole potentials from side chains of Trp, upon either replacement of Trp with a nonpolar amino acid or indole fluorination. [53][54][55][56] The orientation of Trp side chains affects the orientation of the dipole moment and ultimately imposes effects on lowering the overall free energy at the ion-binding site and hence the ion permeation. Table 1 summarizes the dihedral angles of Trp side chains, χ 1 and χ 2 , in the presence and absence of halothane.…”

“…Orientations of Tryptophan Residues. Many lines of experimental evidence indicate that Trp residues are critical to the function of the gA channel. − In addition to their role as anchoring residues at the lipid−water interface to stabilize the channel in the transmembrane orientation, Trp residues at the entrance region of gA are important for ion permeation through noncontact dipole effects. It has been shown that the channel conductance can be modulated by modification of electrical dipole potentials from side chains of Trp, upon either replacement of Trp with a nonpolar amino acid or indole fluorination. − The orientation of Trp side chains affects the orientation of the dipole moment and ultimately imposes effects on lowering the overall free energy at the ion-binding site and hence the ion permeation.…”

“…Many lines of experimental evidence indicate that Trp residues are critical to the function of the gA channel. − In addition to their role as anchoring residues at the lipid−water interface to stabilize the channel in the transmembrane orientation, Trp residues at the entrance region of gA are important for ion permeation through noncontact dipole effects. It has been shown that the channel conductance can be modulated by modification of electrical dipole potentials from side chains of Trp, upon either replacement of Trp with a nonpolar amino acid or indole fluorination. − The orientation of Trp side chains affects the orientation of the dipole moment and ultimately imposes effects on lowering the overall free energy at the ion-binding site and hence the ion permeation. Table summarizes the dihedral angles of Trp side chains, χ 1 and χ 2 , in the presence and absence of halothane.…”

Amino acid sequence modulation of gramicidin channel function: effects of tryptophan-to-phenylalanine substitutions on the single-channel conductance and duration

“…The magnitude of the conductance decrease is roughly proportional to the number of Trp -» Phe substitutions. A similar effect was found on the Cs+ permeability of gramicidins in which two or more Trps were replaced by napthylalanines (Daumas et al, 1989).…”

Gramicidin channels that have no tryptophan residues

“…The increased voltage dependence should vary as a function of the ratio of the dissociation and translocation rate constants [e.g., Andersen (1989)]-the higher the ratio, the steeper the voltage dependence. The present results [and those of Daumas et al (1989Daumas et al ( ,1991] thus suggest that the translocation rate constant is decreased as well; see also Heitz et al (1989). [This conclusion would hold unconditionally if the channels were occupied by at most one ion; but gA channels can be occupied by two Cs+ (Finkelstein & Andersen, 1981), which complicates the analysis.…”

Steered Molecular Dynamics Simulations of Na + Permeation across the Gramicidin A Channel

“…It has been shown that the channel conductance can be modulated by modification of electrical dipole potentials from side chains of Trp, upon either replacement of Trp with a nonpolar amino acid or indole fluorination. [53][54][55][56] The orientation of Trp side chains affects the orientation of the dipole moment and ultimately imposes effects on lowering the overall free energy at the ion-binding site and hence the ion permeation. Table 1 summarizes the dihedral angles of Trp side chains, χ 1 and χ 2 , in the presence and absence of halothane.…”

“…Orientations of Tryptophan Residues. Many lines of experimental evidence indicate that Trp residues are critical to the function of the gA channel. − In addition to their role as anchoring residues at the lipid−water interface to stabilize the channel in the transmembrane orientation, Trp residues at the entrance region of gA are important for ion permeation through noncontact dipole effects. It has been shown that the channel conductance can be modulated by modification of electrical dipole potentials from side chains of Trp, upon either replacement of Trp with a nonpolar amino acid or indole fluorination. − The orientation of Trp side chains affects the orientation of the dipole moment and ultimately imposes effects on lowering the overall free energy at the ion-binding site and hence the ion permeation.…”

“…Many lines of experimental evidence indicate that Trp residues are critical to the function of the gA channel. − In addition to their role as anchoring residues at the lipid−water interface to stabilize the channel in the transmembrane orientation, Trp residues at the entrance region of gA are important for ion permeation through noncontact dipole effects. It has been shown that the channel conductance can be modulated by modification of electrical dipole potentials from side chains of Trp, upon either replacement of Trp with a nonpolar amino acid or indole fluorination. − The orientation of Trp side chains affects the orientation of the dipole moment and ultimately imposes effects on lowering the overall free energy at the ion-binding site and hence the ion permeation. Table summarizes the dihedral angles of Trp side chains, χ 1 and χ 2 , in the presence and absence of halothane.…”