Imperial College London

DrAlexanderWebb

Faculty of MedicineDepartment of Infectious Disease

Research Associate
 
 
 
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Contact

 

+44 (0)20 7594 3058alexander.webb1

 
 
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Location

 

Sir Alexander Fleming BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

14 results found

Kelwick RJR, Ricci L, Chee SM, Bell D, Webb A, Freemont Pet al., 2019, Cell-free prototyping strategies for enhancing the sustainable production of polyhydroxyalkanoates bioplastics, Synthetic Biology, Vol: 3, ISSN: 2397-7000

The polyhydroxyalkanoates (PHAs) are microbially-produced biopolymers that could potentially be used as sustainable alternatives to oil-derived plastics. However, PHAs are currently more expensive to produce than oil-derived plastics. Therefore, more efficient production processes would be desirable. Cell-free metabolic engineering strategies have already been used to optimise several biosynthetic pathways and we envisioned that cell-free strategies could be used for optimising PHAs biosynthetic pathways. To this end, we developed several Escherichia coli cell-free systems for in vitro prototyping PHAs biosynthetic operons, and also for screening relevant metabolite recycling enzymes. Furthermore, we customised our cell-free reactions through the addition of whey permeate, an industrial waste that has been previously used to optimise in vivo PHAs production. We found that the inclusion of an optimal concentration of whey permeate enhanced relative cell-free GFPmut3b production by ∼50%. In cell-free transcription-translation prototyping reactions, GC-MS quantification of cell-free 3-hydroxybutyrate (3HB) production revealed differences between the activities of the Native ΔPhaC_C319A (1.18 ±0.39 µM), C104 ΔPhaC_C319A (4.62 ±1.31 µM) and C101 ΔPhaC_C319A (2.65 ±1.27 µM) phaCAB operons that were tested. Interestingly, the most active operon, C104 produced higher levels of PHAs (or PHAs monomers) than the Native phaCAB operon in both in vitro and in vivo assays. Coupled cell-free biotransformation/transcription-translation reactions produced greater yields of 3HB (32.87 ±6.58 µM) and these reactions were also used to characterise a Clostridium propionicum Acetyl-CoA recycling enzyme. Together, these data demonstrate that cell-free approaches complement in vivo workflows for identifying additional strategies for optimising PHAs production.

Journal article

Webb AJ, Allan F, Kelwick R, Jensen K, Templeton MR, Freemont Pet al., 2018, Protease-based bioreporters for the detection of schistosome cercariae, American Society of Tropical Medicine and Hygiene (ASTMH) 67th Annual Meeting, New Orleans, Louisiana, USA

Conference paper

Webb AJ, Kelwick R, Freemont PS, 2017, Opportunities for applying whole-cell bioreporters towards parasite detection, Microbial Biotechnology, Vol: 10, Pages: 244-249, ISSN: 1751-7915

Journal article

Kelwick RJR, Webb AJ, MacDonald JT, Freemont PSet al., 2016, Development of a Bacillus subtilis cell-free transcription-translation system for prototyping regulatory elements, Metabolic Engineering, Vol: 38, Pages: 370-381, ISSN: 1096-7184

Cell-free transcription-translation systems were originally applied towards in vitro protein production. More recently, synthetic biology is enabling these systems to be used within a systematic design context for prototyping DNA regulatory elements, genetic logic circuits and biosynthetic pathways. The Gram-positive soil bacterium, Bacillus subtilis, is an established model organism of industrial importance. To this end, we developed several B. subtilis-based cell-free systems. Our improved B. subtilis WB800N-based system was capable of producing 0.8 µM GFP, which gave a ~72x fold-improvement when compared with a B. subtilis 168 cell-free system. Our improved system was applied towards the prototyping of a B. subtilis promoter library in which we engineered several promoters, derived from the wild-type Pgrac (σA) promoter, that display a range of comparable in vitro and in vivo transcriptional activities. Additionally, we demonstrate the cell-free characterisation of an inducible expression system, and the activity of a model enzyme - renilla luciferase.

Journal article

Percy M, Karinou E, Webb A, Grundling Aet al., 2016, Identification of a lipoteichoic acid glycosyltransferase enzyme reveals that GW-domain containing proteins can be retained in the cell wall of Listeria monocytogenes in the absence of lipoteichoic acid or its modifications, Journal of Bacteriology, Vol: 198, Pages: 2029-2042, ISSN: 1098-5530

Listeria monocytogenes is a food-borne Gram-positive bacterial pathogen and many of its virulence factors are either secreted proteins, or proteins covalently or non-covalently-attached to the cell wall. Previous work has indicated that non-covalently-attached proteins with GW domains are retained in the cell wall by binding to the cell wall polymer lipoteichoic acid (LTA). LTA is a glycerolphosphate polymer, which is modified in L. monocytogenes with galactose and D-alanine residues. We identified Lmo0933 as the cytoplasmic glycosyltransferase required for the LTA glycosylation process and renamed the protein GtlA for glycosyltransferase LTA A. Using L. monocytogenes mutants lacking galactose or D-alanine modifications or the complete LTA polymer, we show that GW-domain proteins are still retained within the cell wall, indicating that other cell wall polymers are involved in the retention of GW-domain proteins. Further experiments reveal peptidoglycan as the binding receptor as a purified GW domainfusion protein can bind to L. monocytogenes cells lacking wall teichoic acid (WTA) as well as purified peptidoglycan derived from a wild-type or WTA-negative strain. With this, we not only identified the first enzyme involved in the LTA glycosylation process, but we also provide new insight into the binding mechanism of non-covalently attached cell wall proteins.

Journal article

Webb AJ, Kelwick R, Doenhoff MJ, Kylilis N, MacDonald J, Wen KY, Mckeown C, Baldwin G, Ellis T, Jensen K, Freemont PSet al., 2016, A protease-based biosensor for the detection of schistosome cercariae, Scientific Reports, Vol: 6, ISSN: 2045-2322

Parasitic diseases affect millions of people worldwide, causing debilitating illnesses anddeath. Rapid and cost-effective approaches to detect parasites are needed, especially inresource-limited settings. A common signature of parasitic diseases is the release of specificproteases by the parasites at multiple stages during their life cycles. To this end, weengineered several modular Escherichia coli and Bacillus subtilis whole-cell-basedbiosensors which incorporate an interchangeable protease recognition motif into theirdesigns. Herein, we describe how several of our engineered biosensors have been applied todetect the presence and activity of elastase, an enzyme released by the cercarial larvae stageof Schistosoma mansoni. Collectively, S. mansoni and several other schistosomes areresponsible for the infection of an estimated 200 million people worldwide. Since ourbiosensors are maintained in lyophilised cells, they could be applied for the detection of S.mansoni and other parasites in settings without reliable cold chain access.

Journal article

Kelwick R, Webb AJ, Macdonald JT, Freemont PSet al., 2016, Development of a bacillus subtilis cell-free transcriptiontranslation system

Conference paper

Kelwick R, Kopniczky M, Bower I, Chi W, Chin MHW, Fan S, Pilcher J, Strutt J, Webb AJ, Jensen K, Stan G-B, Kitney R, Freemont Pet al., 2015, A Forward-Design Approach to Increase the Production of Poly-3-Hydroxybutyrate in Genetically Engineered Escherichia coli, PLOS ONE, Vol: 10, ISSN: 1932-6203

Journal article

Kelwick R, MacDonald JT, Webb AJ, Freemont Pet al., 2014, Developments in the Tools and Methodologies of Synthetic Biology, Frontiers in Bioengineering and Biotechnology, Vol: 2

Journal article

Webb AJ, Karatsa-Dodgson M, Grundling A, 2009, Two-enzyme systems for glycolipid and polyglycerolphosphate lipoteichoic acid synthesis in Listeria monocytogenes, MOLECULAR MICROBIOLOGY, Vol: 74, Pages: 299-314, ISSN: 0950-382X

Journal article

Basavanna S, Khandavilli S, Yuste J, Cohen JM, Hosie AHF, Webb AJ, Thomas GH, Brown JSet al., 2009, Screening of Streptococcus pneumoniae ABC Transporter Mutants Demonstrates that LivJHMGF, a Branched-Chain Amino Acid ABC Transporter, Is Necessary for Disease Pathogenesis, Infection and Immunity, Vol: 77, Pages: 3412-3423, ISSN: 0019-9567

Journal article

Webb AJ, Homer KA, Hosie AHF, 2008, Two Closely Related ABC Transporters in Streptococcus mutans Are Involved in Disaccharide and/or Oligosaccharide Uptake, Journal of Bacteriology, Vol: 190, Pages: 168-178, ISSN: 0021-9193

Journal article

Webb AJ, Homer KA, Hosie AHF, 2007, A Phosphoenolpyruvate-Dependent Phosphotransferase System Is the Principal Maltose Transporter in Streptococcus mutans, Journal of Bacteriology, Vol: 189, Pages: 3322-3327, ISSN: 0021-9193

Journal article

Webb AJ, Hosie AHF, 2006, A Member of the Second Carbohydrate Uptake Subfamily of ATP-Binding Cassette Transporters Is Responsible for Ribonucleoside Uptake in Streptococcus mutans, Journal of Bacteriology, Vol: 188, Pages: 8005-8012, ISSN: 0021-9193

Journal article

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