... understanding life in molecular detail

Prof Alison Baker

Peroxisomes, Protein trafficking, ABC transporters, Phosphate transport and recycling


My interests are in membrane transport processes in plant cells. Much of my work is related to transport of proteins and metabolites into peroxisomes, essential organelles in all eukaryotes. Recently interests have expanded to encompass the role of membrane proteins in sensing and transporting phosphate, an essential macronutrient for plant growth. Our work is highly collaborative and multidisciplinary ranging from plant physiology and cell biology through protein biochemistry and chemical biology to, hopefully, structural biology in the future.

Current major projects include:
  • Biochemistry of a Peroxisomal ABC transporter protein
  • Synthetic organelles; designer compartments for protein storage
  • Exploiting photosynthetic organisms for P recovery from waste water
  • Plant P sensing and transport proteins for sustainable agriculture

Biochemical Characterisation of the ABC transporter COMATOSE

The import of substrates for peroxisomal β-oxidation, an essential pathway in lipid signalling and metabolism in all organisms, is mediated by members of ATP Binding Cassette (ABC) transporter subfamily D. In our previous BBSRC-funded research we achieved the first purification of such a transporter, the Arabidopsis peroxisomal protein COMATOSE (ABCD1/ CTS), in a form that retained ATPase activity. In a paper recently published in PNAS we demonstrated that insect cell membranes expressing CTS exhibit a novel acyl CoA thioesterase activity which is intrinsic to the transporter. We also showed that CTS is both functionally and physically associated with the peroxisomal Acyl CoA Activating Enzymes (AAEs) LACS6/7, and, together with studies of fatty acid metabolism in yeast, this suggests that thioesterase activity is critical for the transport function not only of CTS but also of many other ABCDs. It is therefore of importance in organisms ranging from fungi and plants to man, where genetic defects in the homologous transporter ALDP result in the serious neurological disorder X-linked adrenoleukodystophy. At present, the molecular mechanisms linking thioesterase activity, AAE binding and fatty acid transport, are unknown, as is the biological function of these linkages. The aim of the proposed research is to understand these mechanisms and their functional roles by characterising the relationships between fatty acyl CoA transport, the ATPase and thioesterase activities of CTS, and the binding of Acyl CoA synthetases and  testing the role of ABCD-dependent thioesterase activity in metabolic regulation.

Collaborators:

Prof S.A. Baldwin (Leeds) http://www.astbury.leeds.ac.uk/people/staff/staffpage.php?StaffID=SAB

Dr Freddie Theodoulou (Rothamsted Research)

http://www.rothamsted.ac.uk/people/theodoul

Prof Ron wanders and Dr Carlo van Roermund (Amsterdam Medical Centre) http://www.amc.nl/web/Research/Who-is-Who-in-Research/Metabolic-disorders.htm?p=6

 

2. Synthetic organelles: manipulating peroxisomal protein import to create designer compartments (Leverhulme Trust).

All but the simplest cells have evolved organelles to provide optimal environments for specific aspects of metabolism such as respiration, photosynthesis or the folding and modification of specific sets of proteins. Photosynthetic organisms are the only source of truly renewable resources, as they alone can convert sunlight into biomass. A body of work has looked at using various plant organelles as biofactories. Unfortunately, a drawback of using an organelle as a ‘biofactory’ is that as more of the desired product is accumulated in the organelle the less well the organelle can perform its natural functions, resulting in a decrease in plant fitness. A generic solution is the production of a synthetic organelle that can perform user-defined functions. Such an organelle will physically separate engineered and endogenous pathways yet still benefit from the metabolic and replicative environment of the cell. This has been achieved for ribosomes but there is insufficient knowledge to achieve this for membrane bound organelles. We are using principles of rational design and molecular evolution to test strategies for the development of synthetic and semisynthetic organelles within plant cells.

Collaborators:

Dr Stuart Warriner (Leeds) http://www.astbury.leeds.ac.uk/people/staff/staffpage.php?StaffID=SLW

Prof Alan Berry (Leeds)

http://www.astbury.leeds.ac.uk/people/staff/staffpage.php?StaffID=ABe

Dr Andrew Cuming (Leeds)

http://www.plants.leeds.ac.uk/people/groups_cum.php

3. IMPACT: Improved Millets for Phosphate Acquisition and Transport. (EU Funded)

This project aims to establish foxtail millet as a model system for studying phosphate acquisition and phosphate use efficiency. Millets are highly nutritious and drought resistant members of the panicoideae. The PHT1 family of membrane transporters is under investigation. We have identified 12 members of this family and are investigating their expression and function to determine whether they can contribute to increased phosphate acquisition or use efficiency.

Collaborators:

Prof S.A. Baldwin (Leeds) http://www.astbury.leeds.ac.uk/people/staff/staffpage.php?StaffID=SAB

4.Investigation of the structure function relationships of Aluminium activated malate channels

TaALMT1 (Triticum aestivum aluminium-activated malate transporter 1) is the founding member of a gene family of plant anion channels with vital roles such as stomatal opening, anion homeostasis, and organic anion efflux. TaALMT1 is part of a sub-group of proteins that play a role in aluminium-detoxification in acid soils, which represent over 50% of potentially arable soils worldwide. Members of this family have been physiologically characterised in planta, and by electrophysiological measurements, but they have not been subject to detailed structural studies.

We aim to express, purify, and characterise members of this family from wheat, Arabidopsis and other plants, as well as homologues from bacteria to gain molecular-level insight into their structure and function. Key to this will be X-ray crystallography, in concert with functional assays and biochemical studies.

Collaborators:

Prof S.A. Baldwin (Leeds) http://www.astbury.leeds.ac.uk/people/staff/staffpage.php?StaffID=SAB

Dr S.P Muench http://www.astbury.leeds.ac.uk/people/staff/staffpage.php?StaffID=SPM

5. Structural and functional investigation of SPX domain proteins from plants.

Plant growth and development is dependent on phosphorus, especially the bioavailable form of inorganic phosphate, which is often limiting in soils. Plants have developed efficient strategies to cope with soil phosphate deficiency including possessing a group of proteins characterized by a highly conserved N-terminal SPX domain, which plays critical roles in maintenance of plant phosphate homeostasis. However, despite the importance of SPX domain-containing proteins, a lack of structural information and details on the nature of their potential binding partners in vivo means that many aspects of how plants respond to phosphate limitation remain poorly understood. We are investigating the structure, potential binding partners and regulation of SPX domain proteins from Arabidopsis and potato.

Collaborators:

Prof S.A. Baldwin (Leeds) http://www.astbury.leeds.ac.uk/people/staff/staffpage.php?StaffID=SAB

Dr S.P Muench http://www.astbury.leeds.ac.uk/people/staff/staffpage.php?StaffID=SPM

Detailed research programme                  Close ▲
ABa.jpg

Professor of Plant cell and Molecular Biology
BA, MA Cambridge, PhD Edinburgh


Lecturer department of Biochemistry, Cambridge 1993-1995
Lecturer, Leeds 1995-1999
Senior lecturer, Leeds 1999-2004
Reader in Plant Cell and Molecular Biology, Leeds 2004-2008

Manton 9.05
School of Molecular and Cellular Biology
0113 343 3045
a.baker@leeds.ac.uk
http://www.fbs.leeds.ac.uk/staff/profile.php?un=bmbalb

Selected Publications

  1. De Marcos Lousa, C. van Roermund, C.W.T. Postis, V.L.G. Dietrich, D Kerr, I.D. Wanders, R.J.A. Baldwin, S.A. Baker, A and Theodoulou, F. L. (2013) Intrinsic acyl-CoA thioesterase activity of a peroxisomal ABC transporter is required for transport and metabolism of fatty acids. Proceedings of the National Academy of Sciences (USA) 110 1279-1284

  2. Paudyal R, Jammaluddin A, Warren JP, Doyle SM Robert S, Warriner SL, Baker A. (2014) Trafficking modulator TENin1 inhibits endocytosis, causes endomembrane protein accumulation at the prevacuolar compartment and impairs gravitropic response in Arabidopsis thaliana. Biochemical Journal 460.177-185

  3. Ceasar, S.A. Hodge A., Baldwin S.A. and Baker A (2014) Phosphate concentration and arbuscular mycorrhizal colonisation influence the growth, yield and expression of twelve PHT1 family phosphate transporters in foxtail millet (Setaria italica). PLoS ONE 9(9): e108459. doi: 10.1371/journal.pone.0108459

  4. Lanyon-Hogg T, Hooper J, Gunn S Warriner SL and Baker A (2014) PEX14 binding to Arabidopsis PEX5 has differential effects on PTS1 and PTS2 cargo occupancy. FEBS letters 588, 2223-2229