Modified amino acids and peptides as substrates for the intestinal peptide transporter PepT1

Abstract

The binding affinities of a number of amino-acid and peptide derivatives by the mammalian intestinal peptide transporter PepT1 were investigated, using the Xenopus laevis expression system. A series of blocked amino acids, namely N-acetyl-Phe (Ac-Phe), phe-amide (Phe-NH 2 ), N-acetyl-Phe-amide (Ac-Phe-NH 2 ) and the parent compound Phe, was compared for efficacy in inhibiting the uptake of the peptideIn an equivalent set of experiments, the blocked peptides Ac-Phe-Tyr, Phe-Tyr-NH 2 and Ac-Phe-Tyr-NH 2 were compared with the parent compound Phe-Tyr. Comparing amino acids and derivatives, only Ac-Phe was an effective inhibitor of peptide uptake (K i 1.81^0.37 mm). Ac-Phe-NH 2 had a very weak interaction with PepT1 (K i 16.8^5.64 mm); neither Phe nor Phe-NH 2 interacted with PepT1 with measurable affinity. With the dipeptide and derivatives, unsurprisingly the highest affinity interaction was with Phe-Tyr (K i 0.10^0.04 mm). The blocked C-terminal peptide Phe-Tyr-NH 2 also interacted with PepT1 with a relatively high affinity (K i 0.94^0.38 mm). Both Ac-Phe-Tyr and Ac-Phe-Tyr-NH 2 interacted weakly with PepT1 (K i 8.41^0.11 and 9.97^4.01 mm, respectively). The results suggest that the N-terminus is the primary binding site for both dipeptides and tripeptides. Additional experiments with four stereoisomers of Ala-Ala-Ala support this conclusion, and lead us to propose that a histidine residue is involved in binding the C-terminus of dipeptides. In addition, a substrate binding model for PepT1 is proposed.

Potential of Amino Acid/Dipeptide Monoester Prodrugs of Floxuridine in Facilitating Enhanced Delivery of Active Drug to Interior Sites of Tumors: A Two-Tier Monolayer In Vitro Study

“…The improvement of oral bioavailability of these antiviral prodrugs has been attributed to their carrier-mediatedtransport by oligopeptide transporters in the gastrointestinal tract (53)(54)(55)(56). A variety of promoieties, including amino acids, dipeptides, tripeptides, and their mimetics, have since been investigated for their suitability as substrates for carrier-mediated oligopeptide and amino acid transporters (57)(58)(59)(60)(61)(62). We have previously described the transport, enzymatic stability, and in vitro antiviral and cytotoxic activity characteristics of amino acid/dipeptide monoester prodrugs of anti-cancer drugs such as floxuridine and anti-virals such as 2-bromo-5,6-dichloro-1-(β-Dribofuranosyl)benzimidazole (BDCRB) and gemcitabine (14,20,21,45,46,63,64).…”

Combined administration of captopril with an antihypertensive Val–Tyr di-peptide to spontaneously hypertensive rats attenuates the blood pressure lowering effect

“…For the epithelial transport via PEPT1, the structural requirements for substrate recognition have been clarified, in which essential structural features to possess are i) a free terminal carboxyl group and ii) at least one peptide bond (Tsuji and Tamao, 1996). The carbonyl group from the peptide bond has also been reported to be essential (Schoenmakers et al, 1999), since it interacts with His 57 from PEPT1 via an ionic interaction as the primary binding site for substrate (Meredith et al, 2000). The amino group has also been reported to be important for the binding to PEPT1 via ionic interactions (Meredith et al, 2000), suggesting that ionizing group(s) at the C-or N-termini in peptides are determinants for substrate recognition.…”

“…The carbonyl group from the peptide bond has also been reported to be essential (Schoenmakers et al, 1999), since it interacts with His 57 from PEPT1 via an ionic interaction as the primary binding site for substrate (Meredith et al, 2000). The amino group has also been reported to be important for the binding to PEPT1 via ionic interactions (Meredith et al, 2000), suggesting that ionizing group(s) at the C-or N-termini in peptides are determinants for substrate recognition. Although captopril and VY both fulfill these requirements for transport, one cannot fully explain their similar affinity toward PEPT1.…”

The Synthesis and Evaluation of Arctigenin Amino Acid Ester Derivatives

“…19) The absorption process of amino acids in the small intestine involves active transport with energy dissipation. 20,21) For example, Zhang et al 22) designed and synthesized diosgenin derivatives and investigated their antitumor activity. These experiments showed that most compounds had a defined activity.…”