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Affilin ® molecules represent a new class of so-called scaffold proteins. The concept of scaffold proteins is to use stable and versatile protein structures which can be endowed with de novo binding properties and specificities by introducing mutations in surface exposed amino acid residues. Complex variations and combinations are generated by genetic methods of randomization resulting in large cDNA libraries. The selection for candidates binding to a desired target can be executed by display methods, especially the very robust and flexible phage display. Here, we describe the construction of ubiquitin based Affilin ® phage display libraries and their use in biopanning experiments for the identification of novel protein ligands.

The glycation compound pyrraline, which originates from the advanced Maillard reaction, appears in urine after consumption of pyrraline-containing food. We hypothesized that the absorption of pyrraline occurs in the form of dipeptides rather than the free amino acid. The human intestinal peptide transporter hPEPT1 was transiently expressed in HeLa cells. In hPEPT1-transfected cells but not in cells transfected with empty vector, the uptake of [(14)C]glycylsarcosine was strongly inhibited by alanylpyrraline (Ala-Pyrr) and pyrralylalanine (Pyrr-Ala). Free pyrraline did not inhibit peptide uptake. In Xenopus laevis oocytes expressing human PEPT1, both Ala-Pyrr and Pyrr-Ala generated significant inward directed currents. In a third approach, uptake of the dipeptides into hPEPT1-transfected HeLa cells was analyzed by HPLC. Ala-Pyrr and Pyrr-Ala were taken up by hPEPT1-expressing cells at a 4- to 7-fold higher rate than by HeLa cells transfected with the empty vector. We conclude that pyrraline containing dipeptides are transported by hPEPT1 in an electrogenic manner into intestinal cells.

The bioactive dipeptide derivative anserine (beta-alanyl-1-N-methyl-L-histidine) is absorbed from the human diet in intact form at the intestinal epithelium. The purpose of this study was to investigate whether anserine is a substrate of the H(+)/peptide cotransporters 1 and 2 (PEPT1 and PEPT2). We first assessed the effects of anserine on [(14)C]glycylsarcosine ([(14)C]Gly-Sar) uptake into Caco-2 cells expressing human PEPT1 and into spontaneous hypertensive rat kidney proximal tubule (SKPT) cells expressing rat PEPT2. Anserine inhibited [(14)C]Gly-Sar uptake with K(i) values of 1.55 mM (Caco-2) and 0.033 mM (SKPT). In HeLa cells transfected with pcDNA3-hPEPT1 or pcDNA3-hPEPT2, K(i) values of 0.65 mM (hPEPT1) and 0.18 mM (hPEPT2) were obtained. We conclude from these data that anserine is recognized by PEPT1 and PEPT2. Carnosine also inhibited [(14)C]Gly-Sar uptake. Using the two-electrode, voltage-clamp technique at Xenopus laevis oocytes, strong hPEPT1-specific inward transport currents were recorded for Gly-Sar, anserine and carnosine, but not for glycine. We conclude that anserine and carnosine interact with the human intestinal peptide transporter and are transported by hPEPT1 in an active, electrogenic H(+) symport. As PEPT1 is the predominant transport system for di- and tripeptides at the intestinal epithelium, this transporter is most probably responsible for the intestinal absorption of anserine after food intake. In addition, anserine might be useful for the design of new substrates of peptide transporters, such as prodrugs, that can be administered orally.

Interleukin-13 (IL-13) is a central regulator of Th2-dominated respiratory disorders such as asthma. Lesions of the airway epithelial barrier frequently observed in chronic respiratory inflammatory diseases are repaired through proliferation, migration and differentiation of epithelial cells. Our work is focused on the effects of IL-13 in human cellular models of airway epithelial cell regeneration. We have previously shown that IL-13 altered epithelial cell polarity during mucociliary differentiation of human nasal epithelial cells. In particular, the cytokine inhibited ezrin expression and interfered with its apical localization during epithelial cell differentiation in vitro. Here we show that CFTR expression is enhanced in the presence of the cytokine, that two additional CFTR protein isoforms are expressed in IL-13-treated cells and that part of the protein is retained within the endoplasmic reticulum. We further show that aquaporin 5 expression, a water channel localized within the apical membrane of epithelial cells, is completely abolished in the presence of the cytokine. These results show that IL-13 interferes with ion and water channel expression and localization during epithelial regeneration and may thereby influence mucus composition and hydration.