Investigating the elevator mechanism in a human nucleoside transporter (hCNT3)

Q. Wu, R.J. Vandenberg and R.M. Ryan, Sydney Medical School, University of Sydney, NSW 2006, Australia.

A new mechanism of transport was proposed by Reyes, Ginter & Boudker in 2009, called the elevator mechanism of transport. Unlike the traditional alternating-access hypothesis, this mechanism has proposed a substrate binding site in a mobile transport domain. After substrate binding, the transport domain undergoes a vertical transition towards the cytoplasm with the bound substrate. This mechanism was first discovered in the archaeal glutamate transporter homologue, Glt_Ph, and was recently proposed to exist in several other transporters from distinct families, including the SLC28 concentrative nucleoside transporter family. Double cysteine mutants of a human nucleoside transporter (hCNT3) were designed with the known inward-facing crystal structures and a repeat-swapped outward-facing model to capture the outward-facing state, which has not been solved. Two successfully cross-linked hCNT3 double cysteine mutants were generated, which provide evidence that the elevator-like movement of the transport domain is crucial for substrate transport in hCNT3. It is also promising that these double cysteine mutants can be crystallised in other conformations, providing a better understanding of how drugs targeting the nucleoside transporters are initially recruited, bind, and are transported into cells.

Reyes N, Ginter C, Boudker O. (2009). Transport mechanism of a bacterial homologue of glutamate transporters. Nature 462, 880-885.