The Section on Molecular Transport, led by Sergey Bezrukov, focuses on transporter-facilitated transport of metabolites and other large solutes across cell and organelle membranes. In the Human Genome there are 43 distinct families of transport systems that comprise more than 300 isoforms of individual solute carriers. Although the majority of the transport systems are responsible for uptake of specific substrates, a substantial number of transporters are used for uptake of the same solute, and overlapping expression of multiple isoforms often exists in the same cell type. Thus, the question arises as to why there are so many transporter isoforms. Though this variety of isoforms may seem redundant and, in principle, could be explained by the lack of strong evolutionary pressures to decrease the size of the genome, the Section's analysis of transporter optimization offers a different interpretation. It has been shown that transporter efficiency is fine-tuned to specific ranges of substrate concentration. Thus, different isoforms might be tailored accordingly, adjusting their amino acid composition for the optimal strength of substrate/transporter interactions and the transition rates between different conformations, with one gene coding for a uniporter protein that functions most efficiently at high solute concentrations and another gene coding for one that is most efficient at low concentrations.
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