X-ray reflectivity study of cyclic peptide monolayers at the air-water interface

The dynamic and living characteristics of monolayers at the air-water interface of a cyclohexapeptide (C6G) and a cyclooctapeptide (C8G), both composed of glutamic acid and 3-aminobenzoic acid subunits in an alternating sequence, were investigated using the Langmuir balance technique, Brewster angle microscopy (BAM), and X-ray reflectivity (XR). An alanine-containing cyclohexapeptide (C6A) was included in this study for comparison. All three cyclopeptides preferentially adopt an orientation parallel to the subphase at low surface pressure. Continuous compression then causes the molecules to flip to a perpendicular state, thus minimizing their molecular area. In contrast to C8G and C6A, a pronounced hysteresis observed during the compression-expansion cycle of C6G indicates that strong intermolecular interactions between the cyclopeptide rings occur in the monolayers of this peptide. This result is supported by BAM measurements that show the formation of crystallite structures for C6G at high surface pressures, whereas no structures were observed for C8G and C6A. These results indicate that C6G is able to self-assemble upon surface compression, an ability that is obviously critically dependent on the correct ring size and composition of the peptide. The presence of hydrogen bond acceptors in the side chains of C6G suggests that the structural stabilization of the monolayer is due to H-bonding, possibly between ring NH groups and side chain CO groups. Our in situ study thus provides a detailed understanding of the molecular dynamics and uninterrupted interfacial behavior of the three peptides in a real-time frame.

[1]  Juan R. Granja,et al.  Antibacterial agents based on the cyclic d,l-α-peptide architecture , 2001, Nature.

[2]  M. Sokabe,et al.  Molecular design and synthesis of artificial ion channels based on cyclic peptides containing unnatural amino acids. , 2001, The Journal of organic chemistry.

[3]  R. Goddard,et al.  Fine Tuning of the Cation Affinity of Artificial Receptors Based on Cyclic Peptides by Intramolecular Conformational Control , 2001 .

[4]  R. Goddard,et al.  A New Cyclic Pseudopeptide Composed of (l)-Proline and 3-Aminobenzoic Acid Subunits as a Ditopic Receptor for the Simultaneous Complexation of Cations and Anions , 1999 .

[5]  S. Kubik.  Large Increase in Cation Binding Affinity of Artificial Cyclopeptide Receptors by an Allosteric Effect , 1999 .

[6]  M. Ghadiri,et al.  Reversible Photoisomerization of Self-Organized Cylindrical Peptide Assemblies at Air−Water and Solid Interfaces , 1999 .

[7]  Sidney R. Cohen,et al.  Crystalline Cyclic Peptide Nanotubes at Interfaces , 1999 .

[8]  R. A. Jishi,et al.  PEPTIDE NANOTUBES : AN INERT ENVIRONMENT , 1998 .

[9]  M. Ghadiri,et al.  Peptide Nanotubes and Beyond , 1998 .

[10]  Norma H. Pawley,et al.  Theoretical Investigation of the Cyclic Peptide System Cyclo(( D-Ala-Glu-D-Ala-Gln)m)1-4) , 1997 .

[11]  Kenji Shiraishi,et al.  Electronic Structures of Protein Nanotubes , 1997 .

[12]  Michele Parrinello,et al.  SELF-ASSEMBLED PEPTIDE NANOTUBES FROM FIRST PRINCIPLES , 1997 .

[13]  H. Ishida,et al.  Serine proteinases mimics: hydrolytic activity of cyclic peptides which include a non-natural amino acid , 1995 .

[14]  H. Ishida,et al.  Highly Effective Binding of Phosphomonoester with Neutral Cyclic Peptides which Include a Non-natural Amino Acid , 1995 .

[15]  Juan R. Granja,et al.  Channel-Mediated Transport of Glucose Across Lipid Bilayers , 1994 .

[16]  Juan R. Granja,et al.  Self-assembling organic nanotubes based on a cyclic peptide architecture , 1993, Nature.

[17]  M. Ghadiri,et al.  Design of an artificial four-helix bundle metalloprotein via a novel ruthenium(II)-assisted self-assembly process , 1992 .

[18]  M. Ghadiri,et al.  A convergent approach to protein design. Metal ion-assisted spontaneous self-assembly of a polypeptide into a triple-helix bundle protein , 1992 .

[19]  Marya Lieberman,et al.  IRON(II) ORGANIZES A SYNTHETIC PEPTIDE INTO THREE-HELIX BUNDLES , 1991 .

[20]  Kenzo Tanaka,et al.  The cyclic dipeptide cyclo[(S)-phenylalanyl-(S)-histidyl] as a catalyst for asymmetric addition of hydrogen cyanide to aldehydes , 1990 .

[21]  L. G. Parratt.  Surface Studies of Solids by Total Reflection of X-Rays , 1954 .