Enkephalins are transported by a novel eukaryotic peptide uptake system

Area of Science:

• Molecular Biology
• Yeast Genetics
• Neuroendocrinology

Background:

• Oligopeptide transport is crucial for cellular functions.
• Endogenous opioids like enkephalins play significant roles in biological systems.
• The mechanisms of enkephalin uptake in eukaryotes remain largely uncharacterized.

Purpose of the Study:

• To identify and characterize a novel oligopeptide transporter in Saccharomyces cerevisiae.
• To investigate the transporter's specificity and functional properties.
• To explore the potential for enkephalin uptake in eukaryotic cells.

Main Methods:

• Gene identification and cloning (OPT1).
• Functional characterization of yeast transport assays using radiolabeled leucine enkephalin.
• Analysis of kinetic parameters (K(m)), pH optimum, and energy dependence.
• Inhibition studies with opioid receptor antagonists.

Main Results:

• Identified the OPT1 gene encoding an oligopeptide transporter.
• Demonstrated uptake of tetra- and pentapeptides, including leucine and methionine enkephalins.
• Transport exhibited saturable kinetics (K(m) = 310 microM), optimal at acidic pH, and energy-dependent.
• Enkephalins were translocated intact, not hydrolyzed.
• Transport was inhibited by naloxone and naltrexone.

Conclusions:

• Saccharomyces cerevisiae possesses a specific oligopeptide transporter (OPT1) capable of importing enkephalins.
• This transporter utilizes enkephalins for growth, indicating their potential as nutrient sources.
• The discovery presents the first eukaryotic system characterized to transport enkephalins, suggesting conserved mechanisms in higher eukaryotes.