Arkansas Chemistry/Biochemistry (retired as of 2-1-21)

Roger E. Koeppe II

Final Report to the National Science Foundation Sept 2022

    My ORCID

    Covers for ACS Omega (supplemental) . . . (March 30, 2021); . . . (August 10, 2021)

    Cover of J Phys Chem B (supplemental) . . . (September 26, 2019)

    Cover of ChemBioChem . . . (March 15, 2016)

    My NCBI Bibliography selections

    (... Selected publications ...)

    (......Students......................)
    (.........Collaborators............)
    (............Research interests..)
GWALP23

Membrane Biochemistry,
Peptide Engineering,
Lipid/Protein Interactions

email: rk2@uark.edu

Our laboratory has primary interests in the regulation of membrane protein function, including the folding and assembly of subunits, hydrophobic matching, and mechanical coupling between proteins and lipids. Systems of study include voltage-dependent ion channels, designed membrane-spanning helical peptides, and mixed lipid systems.

(Selected recent publications and research topics are listed below.)
..
Collaborators: Olaf Andersen, Denise Greathouse, Antoinette Killian.

Former Mentors: Robert M. Stroud, Lubert Stryer.
..
Former Graduate Students: William Lance Whaley, PhD 1986; Bobbie Kuntz, MS 1989; Beverly Davis Meinzer, MS 1989; Ellen Friday, PhD 1990; Martin Jeffrey Taylor, PhD 1992; Jeffrey C Fairman, PhD 1992; Denise V Greathouse, PhD 1993; Kim Chan, PhD 1993; Gwendolyn L Mattice, PhD 1994; Shalendar Mittal, MS 1997; Anthony R Jude, PhD 1998; Robyn Goforth, PhD 2001; Patrick van der Wel, PhD 2002; Sigrid Schmutzer, PhD 2002; Haiyan Sun, PhD 2003; Anna Daily, PhD 2007; Hong Gu, PhD 2008; Chris Mazzanti, PhD 2010; Anne M. Rankenberg, PhD 2010; Vitaly Vostrikov, PhD 2011; Nicholas Gleason, PhD 2012; Venkatesan Rajagopalan, PhD 2016; Ashley N. Martfeld, PhD 2017; Matthew McKay, PhD 2019; Fahmida Afrose, PhD 2019.

Research Interests - Membrane Biophysics

  1. Folding and assembly of proteins within membranes.
  2. Anchor functions of tryptophan (Trp, or W) at the membrane/water interface.

  3. Promotion of ion transport by Trp and fluoro-Trp indoles, and other dipoles.

  4. Role of the peptide backbone for ion transport.
  5. Chemical substitutions within the peptide backbone.
  6. Use of non-genetic amino acids to study protein mechanisms.
  7. Chemical mechanisms for voltage-dependent channel gating.
  8. Development of molecular force transducers to measure the energetics of membrane thinning.
  9. Intrinsic tilt of transmembrane helices.
Y5-GWALP23
Y5-GWALP23
..

Selected publications ---- Roger E. Koeppe II

  1. Martfeld, Ashley N., Denise V. Greathouse and Roger E. Koeppe II (2016) J. Biol. Chem. 291, 19146-19156.
    Ionization Properties of Histidine Residues in the Lipid-Bilayer Membrane Environment. (See this article)

  2. Gleason, Nicholas J., Vostrikov, Vitaly V., Greathouse, Denise V., and Koeppe, Roger E., II (2013) Proc. Natl. Acad. Sci., U. S. A. 110, 1692-1695.
    Buried lysine, but not arginine, titrates and alters transmembrane helix tilt. (See this article)

  3. O'Connell, Ann M., Koeppe, Roger E. II, and Andersen, Olaf S. (1990) Science 250, 1256-1259.
    Kinetics of Gramicidin Channel Formation in Lipid Bilayers - Transmembrane Monomer Association. (See this article)

  4. Koeppe, Roger E. II, and Andersen, Olaf S. (1996) Annu. Rev. Biophy. Biomolec. Struc. 25, 231-258.
    Engineering the Gramicidin Channel. (See this article)

  5. Van der Wel, P.C.A., Strandberg, E., Killian, J.A., and Koeppe, R.E., II (2002) Biophys. J. 83, 1479-1488.
    Intrinsic Tilt of a Tryptophan Anchored Transmembrane alpha-Helix determined using 2H NMR Spectroscopy. (See this article)

  6. De Planque, M.R.R., Kruijtzer, J.A.W, Liskamp, R.M.J., Marsh, D., Greathouse, D.V., Koeppe, R.E. II, de Kruijff, B., and Killian, J.A. (1999) J. Biol. Chem. 274, 20839-20846.
    Different Membrane Anchoring Positions of Tryptophan and Lysine in Synthetic Transmembrane Alpha-Helical Peptides. (See this article)

  7. Jake R. Price, Fahmida Afrose Denise V. Greathouse and Roger E. Koeppe II (2021) ACS Omega 6, 20611-20618.
    Illuminating Disorder Induced by Glu in a Stable Arg-Anchored Transmembrane Helix (See this article)

  8. McKay, Matthew J., Kelsey A. Marr, Jake R. Price, Denise V. Greathouse and Roger E. Koeppe II (2021) ACS Omega 6, 8488-8494.
    Lipid-Dependent Titration of Glutamic Acid at a Bilayer Membrane Interface (See this article)

  9. Afrose, Fahmida, Ashley N. Martfeld, Denise V. Greathouse and Roger E. Koeppe II (2021) BBA Biomembranes 1863, 183501.
    Examination of pH Dependency and Orientation Differences of Membrane Spanning Alpha Helices Carrying a Single or Pair of Buried Histidine Residues (See this article)

  10. McKay, Matthew J., Denise V. Greathouse and Roger E. Koeppe II (2020) FEBS Letters 594, 4280-4291.
    Flanking Aromatic Residue Competition Influences Transmembrane Peptide Helix Dynamics. (See this article)

  11. Pal, Sreetama, Roger E. Koeppe II and Amitabha Chattopadhyay (2021) Faraday Discussions, 232, 330-346.
    Membrane Electrostatics Sensed by Tryptophan Anchors in Hydrophobic Model Peptides Depends on Non-Aromatic Interfacial Amino Acids: Implications in Hydrophobic Mismatch. (See this article)

  12. Afrose, Fahmida, and Roger E. Koeppe II (2020) Biomolecules 10, 273.
    Comparing Interfacial Trp, Interfacial His and pH Dependence for the Anchoring of Tilted Transmembrane Helical Peptides (See this article)

  13. Sustich, Sara J.; Fahmida Afrose; Denise V. Greathouse; and Roger E. Koeppe II (2020) BBA Biomembranes 1862, 183134.
    Influence of Interfacial Tryptophan Residues on an Arginine-Flanked Transmembrane Helix (See this article)

  14. McKay, Matthew J.; Riqiang Fu; Denise V. Greathouse; and Roger E. Koeppe II (2019) J. Phys. Chem. B 123, 8034-8047.
    Breaking the Backbone: Central Arginine Residues Induce Membrane Exit and Helix Distortions Within a Dynamic Membrane Peptide (See this article)
    (Supplemental Cover)

  15. Lipinski, Karli; Matthew J. McKay; Fahmida Afrose; Ashley N. Martfeld; Roger E. Koeppe II; and Denise V. Greathouse (2019) ChemBioChem 20, 2784-2792.
    Influence of Lipid Saturation, Hydrophobic Length and Cholesterol on Double-Arginine-Containing Helical Peptides in Bilayer Membranes (See this article)

  16. Kapoor, Ruchi, Thasin A. Peyear, Roger E. Koeppe II, and Olaf S. Andersen (2019) J. Gen. Physiol. 151, 342-356.
    Antidepressants are modifiers of lipid bilayer properties. (See this article)

  17. Afrose, Fahmida, Matthew J. McKay, Armin Mortazavi, Vasupradha Suresh Kumar, Denise V. Greathouse, and Roger E. Koeppe II (2019) Biochemistry 58, 633-645.
    Transmembrane Helix Integrity versus Fraying to Expose Hydrogen Bonds at a Membrane-Water Interface. (See this article)

  18. McKay, Matthew J., Ashley N. Martfeld, Anna De Angelis, Stanley J. Opella, Denise V. Greathouse, and Roger E. Koeppe II (2018) Biophys. J. 114, 2617-2629.
    Control of Transmembrane Helix Dynamics by Interfacial Tryptophan Residues. (See this article)

  19. Usery, Rebecca D., Thais Enoki, Sanjula Wickramasinghe, Vanessa Nguyen, David Ackerman, Denise Greathouse, Roger Koeppe, Francisco Barrera, and Gerald Feigenson (2018) Biophys. J. 114, 2152-2164. Membrane bending moduli of coexisting liquid phases containing transmembrane peptide. (See this article)

  20. McKay, Matthew J., Fahmida Afrose, Roger E. Koeppe II and Denise V. Greathouse (2018) BBA Biomembranes 1860, 2108-2117.
    Helix Formation and Stability in Membranes. (See this article)

  21. Lum, Kevin, Helgi I.Ingolfsson, Roger E.Koeppe, II, and Olaf S.Andersen (2017) Biophys. J. 113, 1757-1767.
    Exchange of Gramicidin between Lipid Bilayers: Implications for the Mechanism of Channel Formation. (See this article)

  22. Beaven, Andrew H., Alexander J. Sodt, Richard W. Pastor, Roger E. Koeppe II, Olaf S. Andersen, and Wonpil Im (2017) J. Chem. Theory Comput., 13, 5054-5064.
    Characterizing Residue-Bilayer Interactions Using Gramicidin A as a Scaffold and Tryptophan Substitutions as Probes. (See this article)

  23. Rajagopalan, Venkatesan, Denise V. Greathouse and Roger E. Koeppe, II (2017) BBA - Biomembranes 1859, 484-492.
    Influence of glutamic acid residues and pH on the properties of transmembrane helices. (See this article)

  24. Thibado, Jordana K., Ashley N. Martfeld, Denise V. Greathouse and Roger E. Koeppe II (2016) Biochemistry 55, 6337-6343.
    Influence of High pH and Cholesterol on Single Arginine-Containing Transmembrane Peptide Helices. (See this article)

  25. Marquardt, Drew, Heberle, F. A., Greathouse, D., Koeppe, R. E., II, Standaert, R. F., van Oosten, B., Harroun, T. A., Kinnun, J., Williams, J., Steve Wassall, S., and Katsaras, J.
    (2016) Soft Matter 12, 9417-9428. Lipid Bilayer Thickness Determines Cholesterol's Location in Model Membranes. (See this article)

  26. Mortazavi, Armin, Venkatesan Rajagopalan, Kelsey A. Sparks, Denise V. Greathouse, and Roger E. Koeppe II (2016) ChemBioChem 17, 462-465.
    Juxta-Terminal Helix Unwinding as a Stabilizing Factor to Modulate the Dynamics of Transmembrane Helices. (See this article)

  27. Martfeld, Ashley N., Venkatesan Rajagopalan, Denise V. Greathouse, and Roger E. Koeppe II (2015) BBA Biomembranes 1848, 1849-1859.
    Dynamic regulation of lipid-protein interactions. (See this article)

  28. Rusinova, R., Roger E. Koeppe II, and Olaf S. Andersen (2015) J. Gen. Physiol. 146, 463-475.
    A General Mechanism for Drug Promiscuity: Studies with Amiodarone and Other Antiarrhythmics. (See this article)

  29. Sparks, Kelsey A., Nicholas J. Gleason, Renetra Gist, Rebekah Langston, Denise V. Greathouse and Roger E. Koeppe II (2014) Biochemistry 53, 3637-3645.
    Comparisons of Interfacial Phe, Tyr and Trp Residues as Determinants of Orientation and Dynamics for GWALP Transmembrane Peptides. (See this article)

  30. Vorobyov, Igor, Timothy E. Olson, Jung H. Kim, Roger E. Koeppe II, Olaf S. Andersen, and Toby W. Allen (2014) Biophys. J. 106, 586-597.
    Ion-Induced Defect Permeation of Lipid Membranes. (See this article)

  31. Gleason, Nicholas J., Denise V. Greathouse, Christopher V. Grant, Stanley J. Opella, and Roger E. Koeppe II (2013) J. Phys. Chem. B 117, 13786-13794.
    Single Tryptophan and Tyrosine Comparisons in the N-terminal and C-terminal Interface Regions of Transmembrane GWALP Peptides. (See this article)

  32. Vostrikov, Vitaly V., Christopher V. Grant, Stanley J. Opella, and Roger E. Koeppe II (2011) Biophys. J. 101, 2939-2947.
    On the Combined Analysis of 2H and 15N/1H Solid-State NMR Data for Determination of Transmembrane Peptide Orientation and Dynamics. (See this article)

  33. Bruno, Michael J., Radda Rusinova, Nicholas J. Gleason, Roger E. Koeppe II and Olaf S. Andersen (2013) Faraday Discuss. 161, 461-480.
    Interactions of drugs and amphiphiles with membranes: modulation of lipid bilayer elastic properties by changes in acyl chain unsaturation and protonation. (See this article)

  34. Rankenberg, Johanna M., Vostrikov, V. V., Greathouse, D. V., Grant, C. V., Opella, S. J., and Koeppe, R. E., II. (2012) Biochemistry 51, 10066-10074.
    Properties of Membrane-Incorporated WALP Peptides that are Anchored on Only One End. (See this article)

  35. Vostrikov, Vitaly V., Benjamin A. Hall , Mark S. P. Sansom , and Roger E. Koeppe II (2012) J. Phys. Chem. B 116, 12980-12990.
    Accommodation of a Central Arginine in a Transmembrane Peptide by Changing the Placement of Anchor Residues. (See this article)

  36. Rankenberg, Johanna M., Vitaly V. Vostrikov, Christopher D. DuVall, Denise V. Greathouse, Roger E. Koeppe II, Christopher V. Grant, Stanley J. Opella (2012) Biochemistry 51, 3554-3564.
    Proline Kink Angle Distributions for GWALP23 in Lipid Bilayers of Different Thickness. (See this article)

  37. Gleason, Nicholas J., Vitaly V. Vostrikov, Denise V. Greathouse, Christopher V. Grant, Stanley J. Opella, and Roger E. Koeppe II (2012) Biochemistry 51, 2044-2053.
    Tyrosine Replacing Tryptophan as an Anchor in GWALP Peptides. (See this article)

  38. Ingolfsson, Helgi I., Roger E. Koeppe II and Olaf S. Andersen (2011) FEBS Lett. 585, 3101-3105.
    Effects of green tea catechins on gramicidin channel function and inferred changes in bilayer properties. (See this article)

  39. Vostrikov, Vitaly V., and Roger E. Koeppe II (2011) Biochemistry 50, 7522-7535.
    Response of GWALP Transmembrane Peptides to Changes in the Tryptophan Anchor Positions. (See this article)

  40. Gu, Hong , Kevin Lum, Jung H. Kim, Denise V. Greathouse, Olaf S. Andersen and Roger E. Koeppe, II (2011) Biochemistry 50, 4855-4866.
    The Membrane Interface dictates Different Anchor Roles for Inner Pair and Outer Pair Tryptophan Indole Rings in Gramicidin A Channels. (See this article)

  41. Ingolfsson, Helgi I., Yuhui Li, Vitaly V. Vostrikov, Hong Gu, James F. Hinton, Roger E. Koeppe II, Benoit Roux and Olaf S. Andersen (2011) J. Phys. Chem. B, 115, 7417-7426.
    Gramicidin A Backbone and Side Chain Dynamics Evaluated by Molecular Dynamics Simulations and Nuclear Magnetic Resonance Experiments. I: Molecular Dynamics Simulations. (See this article)

  42. Vostrikov, Vitaly V., Hong Gu, Helgi I. Ingolfsson, James F. Hinton, Olaf S. Andersen, Benoît Roux and Roger E. Koeppe II (2011) J. Phys. Chem. B, 115, 7427–7432.
    Gramicidin A Backbone and Side Chain Dynamics Evaluated by Molecular Dynamics Simulations and Nuclear Magnetic Resonance Experiments. II: Nuclear Magnetic Resonance Experiments. (See this article)

  43. Lundbaek, Jens A.; Roger E. Koeppe II; and Olaf S. Andersen (2010) Proc. Natl. Acad. Sci. USA, 107, 15427-30.
    Amphiphile regulation of ion channel function by changes in the bilayer spring constant. (See this article)

  44. Daily, Anna E., Jung H. Kim, Denise V. Greathouse, Olaf S. Andersen, and Roger E. Koeppe II (2010) Biochemistry 49, 6856-6865.
    Polar groups in membrane channels: Consequences of replacing alanines with serines in membrane-spanning gramicidin channels. (See abstract) (See full text)

  45. Yu, Haibo, Christopher L. Mazzanti, Troy W. Whitfield, Roger E. Koeppe II, Olaf S. Andersen, and Benoit Roux (2010) J. Am. Chem. Soc. 132, 10847-10856.
    A combined experimental and theoretical study of ion solvation in liquid N-methylacetamide. (See this article)

  46. Vostrikov, Vitaly V.; Anna E. Daily; Denise V. Greathouse; and Roger E. Koeppe II (2010) J. Biol. Chem., 285, 31723-31730.
    Charged or Aromatic Anchor Residue Dependence of Transmembrane Peptide Tilt. (See this article)

  47. Vostrikov, Vitaly V.; Benjamin A. Hall; Denise V. Greathouse; Roger E. Koeppe II; and Mark S. P. Sansom (2010) J. Am. Chem. Soc., 132, 5803-5811.
    Changes in Transmembrane Helix Alignment by Arginine Residues Revealed by Solid-State NMR Experiments and Coarse-Grained MD Simulations. (See abstract) (See full text)

  48. Andersen, Olaf S.; C. Nielsen; A. M. Maer; J. A. Lundbaek; M. Goulian; and Roger E. Koeppe II (2010)
    Ion Channels as Tools to Monitor Lipid Bilayer-Membrane Protein Interactions: Gramicidin Channels as Molecular Force Transducers.
    In Essential Ion Channel Methods. P. Michael Conn, editor. Academic Press. Burlington. pp. 315-333. (See this article)

  49. Thomas, Rachel, Vitaly V. Vostrikov, Denise V. Greathouse, and Roger E. Koeppe, II (2009) Biochemistry, 48, 11883-11891.
    Influence of Proline upon the Folding and Geometry of the WALP19 Transmembrane Peptide. (See abstract) (See full text)

  50. Vostrikov, Vitaly V., Grant, Christopher V., Daily, Anna E., Opella, Stanley J., and Roger E. Koeppe, II (2008) J. Am. Chem Soc., 130, 12584-85.
    Comparison of 'Polarization Inversion with Spin Exchange at Magic Angle' and 'Geometric Analysis of Labeled Alanines' Methods for Transmembrane Helix Alignment. (See this article)

  51. Sun, Haiyan, Greathouse, Denise V., Andersen, Olaf S., and Roger E. Koeppe, II (2008) J. Biol. Chem., 283, 22233-43.
    On the preference of tryptophan for membrane interfaces: Insights from N-methylation of tryptophans in gramicidin channels. (See this article)

  52. Daily, A.E., Greathouse, D.V., van der Wel, P.C.A and R.E. Koeppe II (2008) Biophys. J. 94, 480-491.
    Helical distortion in tryptophan and lysine anchored membrane-spanning alpha helices as a function of hydrophobic mismatch:
    A solid-state deuterium NMR investigation using the Geometrical Analysis of Labeled Alanines method. (See this article)

  53. Holt, Andrea, de Almeida, R., Nyholm, T., Loura, L., Daily, Anna, Staffhorst, R., Rijkers, D., Koeppe, R.E., II, Prieto, M., and J. A. Killian (2008) Biochemistry 47, 2638-2649.
    Is there a preferential interaction between Cholesterol and Tryptophan residues in membrane proteins? (See this article)

  54. Andersen, O.S., and R.E. Koeppe II (2007) Annual Review Biophys. Biomolec. Struct. 36, 107-130.
    Bilayer Thickness and Membrane Protein Function: An Energetic Perspective. (See this article)

  55. van der Wel, P.C.A., N.D. Reed, D.V. Greathouse, and R.E. Koeppe II (2007) Biochemistry 46, 7514-7524.
    Orientation and Motion of Tryptophan Interfacial Anchors in Membrane-Spanning Peptides. (See this article)

  56. Bruno, M.J., R.E. Koeppe II, and O.S. Andersen (2007) Proc. Natl. Acad. Sci., USA 104, 9638-9643.
    Docosahexaenoic acid alters bilayer elastic properties. (See this article)

  57. Ashrafuzzaman, Md., Lampson, M.A., Greathouse, D.V., Koeppe, R.E., II, and Andersen, O.S. (2006) J. Phys. Condens. Matter 18, S1235-S1255.
    Manipulating lipid bilayer material properties using biologically active amphipathic molecules. (See this article)

  58. Siegel, D.P., V. Cherezov, D.V. Greathouse, R.E. Koeppe, II, J.A. Killian, and M. Caffrey (2006) Biophys. J. 90, 200-211.
    Transmembrane Peptides Stabilize Inverted Cubic Phases in a Biphasic Length-Dependent Manner: Implications for Protein-Induced Membrane Fusion. (See this article)

  59. Pulay, P., E.M. Scherer, P.C.A. van der Wel, and R.E. Koeppe II (2005) J. Am. Chem. Soc. 127, 17488-17493.
    Importance of Tensor Asymmetry for the Analysis of 2H NMR Spectra from Deuterated Aromatic Rings. (See this article)

  60. Andersen, O. S., R. E. Koeppe II, and B. Roux (2005) IEEE Trans. Nanobioscience 4, 10-20.
    Gramicidin Channels. (See this article)

  61. Suchyna, T. M., S. E. Tape, R. E. Koeppe II, O. S. Andersen, F. Sachs, and P. A. Gottlieb (2004) Nature 430, 235-240.
    Bilayer-dependent inhibition of mechanosensitive channels by neuroactive peptide enantiomers. (See this article)

  62. Koeppe, R.E., II, H. Sun, P.C.A. van der Wel, E.M. Scherer, P. Pulay, and D.V. Greathouse (2003) J. Am. Chem. Soc. 125, 12268-12276.
    Combined Experimental/Theoretical Refinement of Indole Ring Geometry Using Deuterium Magnetic Resonance and ab Initio Calculations. (See this article)

  63. Goforth, R.L., A.K. Chi, D.V. Greathouse, L.L. Providence, R.E. Koeppe, II, and O.S. Andersen (2003) J. Gen. Physiol. 121, 477-493.
    Hydrophobic Coupling of Lipid Bilayer Energetics to Channel Function. (See this article)

  64. Hwang, T.-C., R. E. Koeppe, II, and O. S. Andersen (2003) Biochemistry 42, 13646-13658.
    Genistein can modulate channel function by a phosphorylation-independent mechanism: Importance of hydrophobic mismatch and bilayer mechanics. (See this article)

  65. Jude, A.R., Providence, L.L., Schmutzer, S.E., Shobana, S., Greathouse, D.V., Andersen, O.S., and Koeppe, R.E. II (2001) Biochemistry 40, 1460-1472.
    Peptide Backbone Chemistry and Membrane Channel Function: Effects of a Single Amide-to-Ester Replacement on Gramicidin Channel Structure and Function. (See this article)

  66. Demmers, J.A.; van Duijn, E.; Haverkamp, J.; Greathouse, D.V.; Koeppe, R.E. II; Heck, A.J.R.; Killian, J.A. (2001) J. Biol. Chem. 276, 34501-34508.
    Interfacial positioning and stability of transmembrane peptides in lipid bilayers studied by combining hydrogen/deuterium exchange and mass spectrometry. (See this article)

  67. Koeppe, R.E. II, Hatchett, J., Jude, A.R., Providence, L.L., Andersen, O.S., and Greathouse, D.V. (2000) Biochemistry 39, 2235-2242.
    Neighboring aliphatic/aromatic side chain interactions between residues 9 and 10 in gramicidin channels. (See this article)

  68. Greathouse, D.V., Koeppe, R.E., II, Providence, L.L., Shobana, S., and Andersen, O.S. (1999) Methods in Enzymol. 294, 525-550.
    Design and characterization of gramicidin channels.

  69. Jude, A.R., Greathouse, D.V., Koeppe, R.E., II, Providence, L.L., and Andersen, O.S. (1999) Biochemistry 38, 1030-1039.
    Modulation of gramicidin channel structure and function by the aliphatic "spacer" residues 10, 12, and 14 between the tryptophans. (See this article)

  70. De Planque, M.R.R., Kruijtzer, J.A.W., Liskamp, R.M.J., Marsh, D., Greathouse, D.V., Koeppe, R.E. II, De Kruijff, B., and Killian, J.A. (1999) J. Biol. Chem. 274, 20839-46.
    Different membrane anchoring positions of tryptophan and lysine in synthetic transmembrane alpha-helical peptides. (See this article)

  71. Andersen, O.S., Greathouse, D.V., Providence, L.L., Becker, M.D., and Koeppe, R.E., II (1998) J. Am. Chem. Soc. 120, 5142-5146.
    Importance of tryptophan dipoles for protein function: 5-fluorination of tryptophans in gramicidin A channels. (See this article)

    72. The figure below illustrates the effect of the covalent lipid in acylgramicidin on a tryptophan indole ring.

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