Abstract
Peptide transporters mediate the H+-coupled uphill transport of oligopeptides and peptide-like drugs such as beta-lactam antibiotics in the intestinal and renal brush-border membranes. Two H+/peptide cotransporters, PEPT1 and PEPT2, have been cloned and functionally characterized. In this study, we examined the interaction of the dipeptides and beta-lactam antibiotics with the histidine residue of rat PEPT1 and PEPT2 transfected into the renal epithelial cell line LLC-PK1. Diethylpyrocarbonate (DEPC), which is a histidine residue modifier, abolished the glycylsarcosine uptake by both transfectants. The DEPC-induced inhibition of glycylsarcosine uptake via PEPT1 or PEPT2 was attenuated by an excess of dipeptide or aminocephalosporin. In contrast, anionic cephalosporins without an alpha-amino group and bestatin, which is an antineoplastic drug with a beta-amino group, did not attenuate the DEPC-induced inactivation of PEPT1 and PEPT2. The DEPC inactivation of PEPT1 was almost prevented by various charged dipeptides, which suggests that the inability of the drugs without an alpha-amino group to prevent the DEPC inactivation was not due to their ionic charge. These findings suggest that the alpha-amino group of beta-lactam antibiotics interacts with the histidine residue of PEPT1 and PEPT2 and may be involved in the mechanism of substrate recognition by the peptide transporters.
Highlights
In the small intestine and kidney, epithelial assimilation of oligopeptides are mediated by Hϩ-coupled peptide transport systems [1,2,3]
Glycylsarcosine uptake by the PEPT1and PEPT2-expressing transfectants was inhibited by pretreatment with DEPC in the absence and the presence of Hϩ gradient, which suggests that the histidine residue modified by DEPC at least served as the substrate binding site
This could be supported by the fact that the various dipeptides and aminocephalosporins prevented the DEPC-induced inactivation of PEPT1 and PEPT2
Summary
In the small intestine and kidney, epithelial assimilation of oligopeptides are mediated by Hϩ-coupled peptide transport systems [1,2,3]. When PEPT1-expressing cells were treated with diethylpyrocarbonate (DEPC),1 which is a histidine residue modifier, ceftibuten (anionic cephalosporin without an ␣-amino group) uptake was completely abolished [12]. Because histidine residues of the peptide transporters have been indicated as the most important key amino acid residues [12, 15, 16], we investigated the functional role of histidine residues to examine the preventive effect of various substrates on the DEPC-induced inactivation of PEPT1 and PEPT2.
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