PhD student profiles

     
     
   
Felix Schumacher

Marta Wojnowska
Marta joined the ISMB's Wellcome Trust 4-year Interdisciplinary PhD Programme in Autumn 2008.

Project title
Identification of a novel form of hybrid histidine kinase and characterisation of the associated two-component signalling pathway

Principal investigator: Dr Snezana Djordjevic, Structural and Molecular Biology, UCL
Co-investigators: Dr Joanne Santini, Structural and Molecular Biology, UCL

 

Background
During the BSc Genetics course at UCL I undertook a summer project with Dr Chris Kay which involved electron paramagnetic resonance, and after graduation I worked with Dr Rachel McKendry at London Centre for Nanotechnology on imaging of bacterial cells using atomic force microscopy. With this experience I decided to apply for the newly created interdisciplinary Wellcome Trust programme which allowed me to acquire diverse scientific skills.

 

Rotation projects

Prof. Helen Saibil
Processing of negative stain images of colicin bound to two outer membrane proteins

Prof. Charles Marson and Prof. Gabriel Waksman
Attempts at rational design of inhibitors of the attachment of bacterial pili to bladder cells

Prof. David Jones
Modelling the structure of Rhizobium NT-26 arsenite oxidase

 

PhD project
When annotating the two-component “signalome” of Rhizobium NT-26 I have identified an interesting signalling system – the bacteriophytochrome photoreceptor system - which is likely to trigger a yet undetermined type of adaptation in response to changes in red light intensity or temperature. I have extensively characterised this relatively complex form of two-component pathway and shown that it is intrinsically branched. I have also demonstrated that this system involves an unusual type of histidine kinase (ExsG), which, instead of a sensory domain at the amino terminus, contains a phosphorylatable receiver domain, suggesting that the activity of the kinase core is regulated in a phosphorylation-dependent manner. By means of various biochemical assays I have determined that the protein acts as a negative signalling switch within the system; when phosphorylated by the upstream light-sensing protein (BphP1), it prevents one of the two downstream output units (ExsF) from being phosphorylated.

Using analytical ultracentrifugation and electrospray ionisation mass spectrometry I have demonstrated that ExsG, in contrast to all canonical histidine kinases characterised so far, is a homohexamer -  a trimer of dimers. Ion mobility – mass spectrometry experiments, performed in collaboration with the group of Dr Kostas Thalassinos at UCL, provided evidence that ExsG exists in an equilibrium between the active and inactive state of the kinase core. The results led us to propose a model linking two pre-existing conformational states with autokinase activity. ExsG and its associated pathway can be exploited in synthetic biology e.g. in designing in vitro signalling circuits or microbes with programmable properties.

 

 

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