Structural and Functional Studies of Membrane Proteins involved in nutrient uptake and drug transport
Co-workers: Dr Jo Parker, Dr Sabrina Schulze, Nicolae Solcan, John Beale, Sonya Hanson
Research in my laboratory focuses on understanding how nutrient transporters function at a molecular level. In humans many of the transport proteins involved in absorbing nutrients from our diet, such protein, sugar and fats, are also responsible for drug transport and distribution into specific organs, such as the central nervous system, liver and kidneys. Nutrient transporters therefore have a profound impact on the pharmacokinetic properties of many administered drugs with clear medical advantages to understanding their biochemistry.
Peptide transporters belong to one such family of integral membrane transporters, which in mammals are the major route of dietary peptide absorption in the small intestine and kidneys. In humans they belong to the Solute Carrier (SLC) 15 gene family and called PepT1 and PepT2. Both PepT1 and PepT2 are of significant pharmaceutical interest due to their ability to actively uptake a number of clinically important drugs, such as beta-lactam antibiotics, antivirals and HIV protease inhibitors. Recent developments in drug delivery technology have targeted PepT1 and PepT2 to improve the pharmacokinetic properties of such drugs, including their uptake and retention within the body. Following attachment of amino acids or small peptides to a drug that has poor absorption properties, these called peptide pro drugs are now recognized by PepT1 and transported into the body following oral administration (Figure A). The potential of utilizing PepT1 and PepT2 as universal drug delivery and retention systems represents a profound and transformative new development in engineered drug bioavailiabity.
One of the key goals of our research is to extend the use of protein crystallography and in vitro biochemical analysis to provide novel insights into the molecular details underpinning the observed peptide and drug recognition properties within the SLC15 peptide transporter family.
We have determined the first crystal structures for two prokaryotic peptide transporters from the bacteria Shewanella oniedensis (PepTSo) and Streptococcus thermophilus (PepTSt). These structures have provided detailed 3D atomic models for the Proton dependent Oligopeptide Transporter (POT) family, to which the mammalian PepT1 and PepT2 proteins belong (Figure B & C). Recently we also determined the first crystal structure for eukaryotic member of the POT family, the plant nitrate transporter NRT1.1. This structure along with biophysical studies on nitrate binding revealed the molecular basis for a phosphorylation-controlled switch in the Km of this protein, an evolutionary adaption to changes environmental concentrations of nitrate.
Membrane protein crystal screen development: The MemGold family.
The development of new methods to determine the crystal structures of membrane proteins is also an important part of our research. In addition to work in developing expression and screening technologies to identify suitable targets for biophysical study, we are also data mining the Protein Data Bank (PDB) to uncover emerging trends in alpha helical membrane protein crystallization. This information is then used to develop more sophisticated membrane protein crystallization screens. We have recently launched complimentary screens to the highly successful MemGold screen, which was launched in 2007, called MemGold II and MemAdvantage. MemGold II employs information from a range of recently determined eukaryotic membrane protein structures, whilst MemAdvantage is the first additive screen designed specifically for membrane protein crystal optimization. These screens are available through our industrial partner Molecular Dimensions Ltd.
- Parker, JL. & Newstead, S. Molecular basis of nitrate uptake by the plant nitrate transporter NRT1.1. Nature 507, 68-72.
- Moraes, I. et al., Membrane Protein structure determination – the next generation. BBA 1838, 78-87. 2013
- Lee, C. et al., A two-domain elevator mechanism for sodium/proton antiport. Nature 501, 573-577.
- Parker JL. & Newstead, S. Phasing statistics for alpha helical membrane protein structures. Protein Science. 22, 1664-8.
- Doki, S., et al. Structural basis for dynamic mechanism of proton-coupled symport by the peptide transporter POT. PNAS 110, 11343-8. 2012
- Parker, J., Newstead, S. Current trends in alpha helical membrane protein crystallization; an update. Protein Science. 21, 1358-1365.
- Solcan, N., et al. Alternating access mechanism in the POT family of oligopeptide transporters. EMBO J. 31, 3411 - 3421.
News articles relating to research in the Newstead group:
Figure A: PepT1 and PepT2 play key roles in mediated drug transport in the human body. Illustrated here the concept of peptide pro-drug transport
Figure B: Alternating access mechanism of transport in the POT family, determined through structural and biochemical studies undertaken in the group
Figure C: Crystal structure of PepTSo, a bacterial homologue of PepT1, shown in an simulated POPC bilyer used to study protein dynamics via molecular dynamics. Valacicolvir, a commonly prescribed peptide pro-drug transported into the body via PepT1
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