Transporter tandems: precise tools for normalizing active transporter in the plasma membrane.

Area of Science:

• Biochemistry
• Molecular Biology
• Pharmacology

Background:

• Accurate comparison of transporter protein performance requires monitoring active transporters in the plasma membrane.
• Existing methods for quantifying active transporters are often imprecise, laborious, or fail to distinguish between intracellular and plasma membrane-localized proteins.

Purpose of the Study:

• To develop a novel method for normalizing the number of active transporters using transporter tandems.
• To assess the impact of linker sequences on tandem construct expression and stoichiometry.
• To validate the utility of transporter tandems for accurate transporter number normalization.

Main Methods:

• Generation of transporter tandems by fusing cDNA of the human ergothioneine transporter (ETT) and organic cation transporter 2 (OCT2) with varying linkers.
• Validation of 1:1 stoichiometry using absolute and untargeted peptide quantification.
• Assessment of transport efficiency and functional activity of wild-type and variant transporters within tandem constructs.

Main Results:

• Linker sequences significantly influenced the expression levels of transporter tandems.
• Stoichiometry was confirmed through peptide quantification.
• Normalized ergothioneine clearance was higher for a natural ETT variant (L503F) compared to wild-type ETT, while another variant (G462E) was inactive.
• Constructs linking ETT with other transporters demonstrated the general applicability of the tandem strategy.

Conclusions:

• Transporter tandems offer a precise and efficient tool for normalizing active transporter numbers without the need for membrane isolation or protein quantification.
• This strategy facilitates the identification of relevant transporters, such as those involved in drug transport.
• Optimization of linker sequences, transporter order, and assessment of potential functional interference are crucial for successful implementation.