Hydrophobic Peptide Channels and Encapsulated Water Wires

Raghavender, Upadhyayula S and Kantharaju, * and Aravinda, Subrayashastry and Shamala, Narayanaswamy and Balaram, Padmanabhan (2010) Hydrophobic Peptide Channels and Encapsulated Water Wires. In: Journal of Physics: Condensed Matter, 132 (3). pp. 1075-1086.

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Abstract

Peptide nanotubes with filled and empty pores and close-packed structures are formed in closely related pentapeptides. Enantiomorphic sequences, Boc-(D)Pro-Aib-Xxx-Aib-Val-OMe (Xxx = Leu, 1; Val, 2; Ala, 3; Phe, 4) and Boc-Pro-Aib-(D)Xxx-Aib-(D)Val-OMe ((XXX)-X-D = (D)Leu, 5; (D)Val, 6; (D)Ala, 7; (D)Phe, 8), yield molecular structures with a very similar backbone conformation but varied packing patterns in crystals. Peptides 1, 2, 5, and 6 show tubular structures with the molecules self-assembling along the crystallographic six-fold axis (c-axis) and revealing a honeycomb arrangement laterally (ab plane). Two forms of entrapped water wires have been characterized in 2: 2a with d(O center dot center dot center dot O) = 2.6 angstrom and 2b with d(O center dot center dot center dot O) = 3.5 angstrom. The latter is observed in 6 (6a) also. A polymorphic form of 6 (6b), grown from a solution of methanol-water, was observed to crystallize in a monoclinic system as a close-packed structure. Single-file water wire arrangements encapsulated inside hydrophobic channels formed by peptide nanotubes could be established by modeling the published structures in the cases of a cyclic peptide and a dipeptide. In all the entrapped water wires, each water molecule is involved in a hydrogen bond with a previous and succeeding water molecule. The O-H group of the water not involved in any hydrogen bond does not seem to be involved in an energetically significant interaction with the nanotube interior, a general feature of the one-dimensional water wires encapsulated in hydrophobic environements. Water wires in hydrophobic channels are contrasted with the single-file arrangements in amphipathic channels formed by aquaporins.

Item Type:	Journal Article
Publication:	Journal of Physics: Condensed Matter
Publisher:	Institute of Physics.
Additional Information:	Copyright of this article belongs to Institute of Physics.
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	29 Mar 2010 07:57
Last Modified:	19 Sep 2010 05:57
URI:	http://eprints.iisc.ac.in/id/eprint/26392

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