A Randomly Coiled, High-Molecular-Weight Polypeptide Exhibits Increased Paracellular Diffusion in Vitro and in Situ Relative to the Highly Ordered -Helix Conformer

Authors: Salamat-Miller, Nazila¹; Chittchang, Montakarn¹; Mitra, Ashim K.¹; Johnston, Thomas P.²

Source: Pharmaceutical Research, Volume 22, Number 2, February 2005 , pp. 245-254(10)

Publisher: Springer

Abstract:

The current investigation was conducted to examine the effect of secondary structure of model polypeptides on their hindered paracellular diffusion.

Poly-d-glutamic acid (PDGlu) was selected as one of the model polypeptides because of its ability to form two secondary structures; a negatively charged random coil and an -helix with partial negative charge at pH 7.4 and 4.7, respectively. Poly-d-lysine (PDL) was selected as a positively charged random coil conformation at pH 7.4. Transport experiments were conducted across both a Caco-2 cell monolayer and the intestinal membrane of Sprague-Dawley rats. Additionally, using NMR, an estimation for the diffusion coefficient and the equivalent hydrodynamic radius for each model polypeptide was obtained.

PDGlu in the randomly coiled conformation exhibited greater paracellular transport when compared to either the same polypeptide having an -helix secondary structure or the positively charged, randomly coiled PDL.

Randomly coiled PDGlu was able to permeate through the negatively charged tight junctions of both biological membranes to a greater extent than PDGlu having an -helix structure and suggests that molecular flexibility associated with the random coil conformation may play a more important role than overall charge and hydrodynamic radius on its hindered paracellular diffusion.

Keywords: paracellular diffusion; polypeptide; secondary structure; molecular geometry

Document Type: Research article

DOI: http://dx.doi.org/10.1007/s11095-004-1192-4

Affiliations: 1: Division of Pharmaceutical Sciences, School of Pharmacy, University of Missouri-Kansas City, Kansas City, Missouri, 64110, USA, 2: Division of Pharmaceutical Sciences, School of Pharmacy, University of Missouri-Kansas City, Kansas City, Missouri, 64110, USA, Email: johnstont@umkc.edu

Publication date: 2005-02-01

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