title: A randomly coiled, high-molecular-weight polypeptide exhibits increased paracellular diffusion in vitro and in situ relative to the highly ordered alpha-helix conformer.
abstract: OBJECTIVE
  The current investigation was conducted to examine the effect of secondary structure of model polypeptides on their hindered paracellular diffusion.
  
  
  METHODS
  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 alpha-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.
  
  
  RESULTS
  PDGlu in the randomly coiled conformation exhibited greater paracellular transport when compared to either the same polypeptide having an alpha-helix secondary structure or the positively charged, randomly coiled PDL.
  
  
  CONCLUSIONS
  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 alpha-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.
authors.affiliation: Division of Pharmaceutical Sciences, School of Pharmacy, University of Missouri-Kansas City, Kansas City, Missouri 64110, USA.
authors.forename: Nazila
authors.initials: N
authors.lastname: Salamat-Miller
authors.forename: Montakarn
authors.initials: M
authors.lastname: Chittchang
authors.forename: Ashim K
authors.initials: AK
authors.lastname: Mitra
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Johnston
mesh_terms: D000818:Animals; D018938:Caco-2 Cells; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D004058:Diffusion; D006801:Humans; D007408:Intestinal Absorption / Q000502:physiology*; D007413:Intestinal Mucosa / Q000378:metabolism*; D008297:Male; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism*; D017433:Protein Structure, Secondary / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D010455:Peptides