PhD Studentship: Seeing sodium ions in membrane transporters

Website DiamondLightSou Diamond Light Source

Supervisors & University

University: Imperial College London
University Supervisor: Dr. Konstantinos Beis
University Group: Department of Life Sciences
Diamond Supervisor: Dr. Armin Wagner
Diamond Group: I23 Beamline

Project Description

Transport of molecules across membranes is an essential mechanism for cell growth and survival, or to detoxify them from toxic compounds. Primary active transporters harness the energy from ATP hydrolysis to transport molecules against a concentration gradient, while secondary active transporters use the energy stored in concentration gradients of protons or ions. Some secondary transporters utilise the Na+ gradient across membranes, created by other transporters that actively pump Na+ out of the cell, to drive the uptake of solutes into the cell. Sodium-dependent transporters can be found across all kingdoms of life. The structures of several sodium-dependent transporters have been determined but due to its small size it is difficult to directly distinguish a sodium cation from a water molecule. Therefore, indirect methods are utilised, identifying these sites by structural considerations, like geometry and coordination, further validated by mutagenesis. Alternatively, sodium sites can be ‘determined’ by substitution of sodium with heavier mono-valent cations such as rubidium or thallium and analysis of either isomorphous or anomalous electron density difference maps. To-date, there is no report of directly observing a sodium cation bound to a protein.

During this work, we want to develop novel methods to ‘visualise’ the bound sodium on membrane proteins (also applicable to soluble proteins) based on long-wavelength X-ray crystallography in a wavelength range of around 5 Å which will allow a direct, unambiguous determination of sodium sites directly from the anomalous signal from sodium present at such long wavelengths. We will also perform biochemical assays to further characterise these sites and their role in the function of the transporters. The work will refine our understanding on how these transporters operate since many of them are involved in diseases.


This project is based at Research Complex at Harwell, and Diamond Light Source Ltd, both of which are part of the the Rutherford Appleton Laboratory, Harwell, Oxfordshire

Studentship Deliverables

The main deliverables of this studentship are:

  1. develop novel methods to identify sodium-bound cations in proteins,
  2. characterise the sodium binding sites of membrane transporters,
  3. link sodium cations to protein function,
  4. exploit methods to optimise crystal size and shape for optimal data collection


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