Membrane sensory proteins and environmental cues of Enterococcus faecalis

Lead Research Organisation: University of Leeds
Department Name: Inst of Molecular & Cellular Biology

Abstract

Disease-causing bacteria depend on being able to sense (and respond to) changes in their environment in order to survive and multiply in their host and surroundings. They have evolved specific sensory proteins located in their outer layers (the membrane), and they use the information from these proteins to switch on/off production of virulence and other disease-enhancing factors (e.g. toxins). Almost every pathogenic bacterium possesses these sensory proteins, and the most common group are known as two-component signal transduction systems (TCSs). They consist of a sensor kinase protein (SK, usually located in the membrane) that senses the outside environmental signal, and a partner response regulator protein (RR) located inside the cell that receives the SK information and effects a response /usually a change in the expression of various genes, including those encoding virulence factors. Most bacteria possess multiple TCS pairs, each one tuned in to a different specific environmental cue. For example, the infective bacterium Enterococcus faecalis possesses 17 TCS pairs. This bacterium is an important pathogen of humans -causing endocarditis, urinary tract and bloodstream infections, wound infections and infections of indwelling foreign devices, and is of additional concern because of its readily acquired resistance to a wide range of antibiotics including last-line glycopeptide antibiotics such as vancomycin. Enterococci have now become the second most important agent of hospital-infections. The aim of this proposal is to study the 17 SKs of E. faecalis, in order to understand what environmental signals are being sensed, how the proteins respond to their signal, how signal information is passed across the membrane, and ultimately the atomic structures of the proteins. We will prioritise the 9 SKs that are implicated in virulence, but structural knowledge of any will be highly informative. To achieve these aims, we must study the SKs in their intact forms, complete with membrane spanning portions, and we have the relevant specialist expertise for this. Ultimately, such studies will lead to new strategies to combat infections by E. faecalis that are based on inhibitors of these signal sensing/transduction systems, including those involved in activation of virulence factors and/or host defence systems.

Technical Summary

Using Enterococcus faecalis as a model infection agent, the three specific objectives of this proposal are as follows. (1) Build on our specialist expertises and successes with the SK group of membrane proteins by overexpressing and purifying the full complement of 16 membrane (and 1 soluble) SKs in this bacterium in their intact form (prioritising the 9 known or predicted virulence-associated sensors). (2) Identify or confirm the signals/ligands that interact with these proteins. We will use a range of candidate and other signal molecules in SK phosphorylation assays to identify the external signals sensed by these SKs; some already have known or strong candidates. (3) Identify the structural changes that occur in these proteins upon ligand (signal) binding using FTIR, fluorescence and CD spectroscopy, with stopped-flow measurements as appropriate. Finally, we will undertake crystallisation trials to initiate structural characterisation. Ultimately, knowledge of the structure and the environmental triggers (ligands) identified by these proteins will be used to devise strategies that inactivate ligand-protein binding, affecting signal sensing and therefore virulence activation. This project exploits a structural genomics approach for elucidating key environmental responses of a pathogenic microorganism.

Publications

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Henderson P.J.F. (2007) Bacterial membrane drug efflux and receptor proteins. in Drugs of the Future

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Patching, S.G. (2012) NMR methods for structure-function investigation of membrane proteins and their ligands in Journal of Labelled Compounds and Radiopharmaceutics

 
Description All the objectives of the grant were met (described below) and several further discoveries were accomplished (also indicated below):

1. Objective 1: Of 16 intact membrane sensor proteins (MSKs) targeted for expression and characterisation, fifteen were found to be successfully expressed and thirteen purified and demonstrably active by novel assays. Conditions for overexpression and purification were optimised for some proteins (those important for virulence and those that express/purify less well initially). This is a good rate of success for such technically-challenging hydrophobic proteins. Successful publication on the conditions required for successful expression and purification of this class of membrane proteins, on the activities of the resultant purified proteins by in vitro assays, and the activities in reponse to challenge with ligands was achieved. The work established that the technology employed is successful for producing pure and intact versions of these sensor kinases (one of the main aims of the grant, and published (Mol. Membr. Biol. (2008)).

2. Objective 2: Signal (ligand) screening was developed and conducted for ten proteins and signals successfully identified for four proteins using autophosphorylation activity assays. Signal identification was carried out through use of purified proteins (rather than membrane-bound proteins (technically more challenging), as was also proposed in the original application). The effect of signals on the dephosphorylation activities of the MSKs was also investigated for the VicK-VicR system and although there was no direct effect of the signal through dephosphorylation, the kinetics were reported in a publication (Mol Membr. Biol. (2008)).

3. Objective 3: The techniques of CD and fluorescence spectroscopy were explored for suitability for investigating ATP and ligand binding, as proposed in the original grant proposal. CD spectroscopy emerged as a particularly successful approach, and therefore the other approaches proposed were not pursued further. MSK-ligand interactions were investigated for the FsrC MSK, which interacts with a small pheromone (GBAP). The interaction was explored for the first time using SRCD (at Diamond Light Source) and quantitative ligand binding data obtained. The 2 uM kd value obtained for the binding of GBAP to FsrC indicated relatively tight binding for the ligand, especially compared with those typical of transporter membrane proteins. This is the first time that SRCD spectroscopy has been used to determine a Kd value for ligand binding by any membrane protein and was published in Biochim. Biophys. Acta Biomembranes (2012). ATP binding was also investigated using SRCD spectroscopy and fluorescence methods, and once again SRCD spectroscopy proved to be the more suitable approach.


4. Nine proteins were suitable for crystallisation trials. In the original grant application crystal trials were to be set up as proteins became available and as time permitted. Trials were undertaken for the majority of these proteins, and promising crystals were obtained for some of these intact MSKs; this aspect is being continued. In addition, an opportunity arose during the grant lifetime, to determine the three-dimensional structure of VicRc (a partner protein that interacts with one of the intact MSKs (VicK) sensor kinases under study in the grant and important because the VicKR system is considered an essential system and therefore a particularly good drug target). The work was published in Acta Crystallograph. Series D (2007).

5. Over and above the original objectives of the grant, the following relevant work was also accomplished:

5.1 During objectives 2 and 3, antagonist ligands (inhibitors), as well as native agonist ligands as originally proposed, were identified for some MSKs. Specifically, the anti-enterococcal drug siamycin I was shown by the grant to be a direct inhibitor of the activity of the FsrC quorum MSK, providing direct evidence that membrane sensor kinases are druggable/targetable (published in FEBS Letters, 2011). Siamycin I interactions with FsrC were also demonstrated using SRCD spectroscopy and binding was found to occur at an independent site in FsrC to GBAP binding (published in Phys Chem Chem Phys, 2013).

5.2 . During the development of SRCD spectroscopy to study the intact FsrC membrane protein, it was found to be a sensitive method for monitoring stability of membrane proteins within micelllar complexes and therefore a valuable tool for membrane protein crysallographers to ensure protein stability prior to setting up crystal trials (protein stability being essential for optimal crystallisation success)(published in Biochim Biophys Acta Biomembr., 2012).

All aspects of the work described above have been published in peer-reviewed journals, resulting in six (6) publications.

NB 16 membrane sensor kinases were investigated, rather than the 17 originally proposed, as it turned out that only 16 are membrane proteins.
Exploitation Route Implications for the pharmaceutical industry.

1. Intact membrane sensor kinases are druggable. This is the first time that this has been established for a genome complement of proteins and by an in vitro approach, paving the way for drug screening.

2. Our findings that SRCD spectroscopy can be used as a sensitive tool for monitoring membrane protein (FsrC) stability within detergent micelles prior to undertaking further studies has been adopted by membrane protein biologists to screen for membrane protein stability prior to undertaking crystal trials of purified proteins.

3. SRCD spectroscopy is now being used to determine quantitative ligand and inhibitor binding by these membrane proteins.

4. Crystal trials are being continued in collaborations with UK and EU partners. A successful outcome to this long term goal of obtaining the first crystal structure for a member of this protein family would be very important implications for drug design.

5. Follow on funding to use some of the technologies developed during the grant (and afterwards) to develop a device to detect bacterial infections.
Sectors Education

Healthcare

Pharmaceuticals and Medical Biotechnology

 
Description The grant led to a Follow-on Pathfinder grant BB/M013081/1. The grant was also essential for leading us into work with colleagues at Diamond Light Source Ltd. In collaboration with Siligardi and Hussain, we applied SRCD spectroscopy for the investigation of ligand and inhibitor binding to membrane proteins (specifically the membrane sensor kinases of the grant and acquisition of quantitative binding data). This had academic impact not only for those working in the field of bacterial signal transduction and gene regulation, but also because the technique is now being applied by others in the academic community working with membrane proteins (which are also often promising drug targets). Impact for academic community: 1. first application of SRCD spectroscopy for quantitating ligand and inhibitor interactions with membrane proteins. The technique employs smaller amounts of precious low yielding membrane proteins, making it feasible to undertake the numerous titrations needed in order to obtain quantitative data such as kd values; 2. identification of SRCD spectroscopy as a useful pre-screen of membrane protein stability in samples prior to their use in crystallisation or other downstream applications. For example, it is well recognised that the availability of stable protein preparations are essential for optimising crystallisation success. During our work at the synchotron using SRCD, which could not have taken place without the work accomplished in the grant, we sometimes identified unexpected instability of the membrane proteins in detergent micelles. We utilised SRCD as a screen to establish the right conditions for stability prior to obtaining spectral data on its ligand interactions. The same approach can be adopted for ensuring sample stability prior to setting up crystallisation trials of membrane proteins (many of which are important drug targets). We are aware of membrane protein crystallographers adopting this new approach which emerged during our work arising from the grant. 3. Establishment of new collaborations with membrane protein crystallographers, membrane biologists and microbiologists in the UK and internationally (with Siligardi & Hussain (Diamond Light Source), Archer (Lisbon), Nakayama (Japan), de Moraes (Membrane Protein Lab, Diamond), Courvalin (antibiotic resistance mechanisms, Paris), Patching (NMR,Leeds).
First Year Of Impact 2009
Sector Environment,Healthcare,Pharmaceuticals and Medical Biotechnology
Impact Types Cultural

 
Description A high-throughput protein expression facility for structural and cell biology'
Amount £233,156 (GBP)
Funding ID BB/E013163/1 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 01/2007 
End 12/2007
 
Description BBSRC Pathfinder
Amount £19,000 (GBP)
Funding ID BB/M013081/1 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 09/2014 
End 04/2015
 
Description Diamond-UCLan Postgraduate Studentship
Amount £96,000 (GBP)
Organisation University of Central Lancashire 
Sector Academic/University
Country United Kingdom
Start 09/2013 
End 09/2017
 
Title Quantitative binding data for membrane proteins via circular dichroism 
Description Synchrotron radiation circular dichroism can be used to obtain kd values for ligand interactions with membrane proteins; our research used this technique for kd value determination for the first time for membrane proteins. 
Type Of Material Biological samples 
Year Produced 2012 
Provided To Others? Yes  
Impact Unknown 
 
Title Use of circular dichroism to screen for membrane protein stability 
Description Synchrotron radiation circular dichroism can be used to screen for the stability of membrane proteins in detergent micelles. This can be useful prior to use of membrane proteins in crystallisation trials in which protein stability is paramount. Optimisations of buffer and other conditions can be screened using SRCD to determine those conditions that are optimal for protein stability 
Type Of Material Biological samples 
Year Produced 2012 
Provided To Others? Yes  
Impact Other local research groups involved in crystallography use SRCD as a screen now. 
 
Description Collaboration at Diamond Light Source 
Organisation Diamond Light Source
Country United Kingdom 
Sector Private 
PI Contribution New collaboration at beamline 23 of Diamond Light Source (synchotron radiation circular dichroism). Training and guidance in the use of SRCD, and a new collaboration on its use to study membrane proteins. Outcome was the first kd data for membrane proteins to be obtained using SRCD.
Collaborator Contribution CD facilities and training, beamtime allocation
Impact Hussain, R., Hughes, C.S., Ma, P., Harding, S.E., Patching, S.G., Edara, S., Siligardi, G., Henderson, P.J.F. & Phillips-Jones, M.K. Purification of bacterial membrane sensor kinases and biophysical methods for determination of their ligand and inhibitor interactions. Biochem. Soc. Trans. (accepted). (IF 3.194). Phillips-Jones, M.K. (2014) Editorial: Structural and biophysical characterisation of membrane protein-ligand binding. Biochimica et Biophysica Acta - Biomembranes. 1838 Issue 1 Part A 1-2 (IF 3.919) Siligardi, G., Hussain, R., Patching, S.G. & Phillips-Jones, M.K. (2014). Ligand- and drug-binding studies of membrane proteins revealed through circular dichroism spectroscopy. Biochim. Biophys. Acta Biomembr. 1838: 34-42. (IF 3.919) Phillips-Jones, M.K., Patching, S.G., Edara, S., Nakayama, J., Hussain, R., & Siligardi, G. (2013). Investigation of the first step of a virulence regulatory pathway in a bacterial hospital-acquired infection agent. Diamond Light Source Annual Review 2012/13. pp30-31. Phillips-Jones, M.K., Patching, S.G., Edara, S., Nakayama, J., Hussain, R., & Siligardi, G. (2013) Interactions of the intact FsrC membrane histidine kinase with the tricyclic peptide siamycin I revealed through synchrotron radiation circular dichroism. Phys. Chem. Chem. Phys. 15, 444-447. (IF 3.829) Patching, S.G., Edara, S., Ma, P. Nakayama, J., Hussain, R., Siligardi, G. & Phillips-Jones, M.K. (2012) Interactions of the intact FsrC membrane histidine kinase with its pheromone ligand GBAP revealed through synchrotron radiation circular dichroism. Biochim. Biophys. Acta Biomembr. 1818, 1595-1602. (IF 3.919)
Start Year 2010
 
Description Collaboration with National Centre for Macromolecular Hydrodynamics 
Organisation University of Nottingham
Department School of Biosciences
Country United Kingdom 
Sector Academic/University 
PI Contribution Provision of intact membrane sensor kinases
Collaborator Contribution Provision of analytical ultracentrifugation facilities
Impact Hussain, R., Hughes, C.S., Ma, P., Harding, S.E., Patching, S.G., Edara, S., Siligardi, G., Henderson, P.J.F. & Phillips-Jones, M.K. Purification of bacterial membrane sensor kinases and biophysical methods for determination of their ligand and inhibitor interactions. Biochem. Soc. Trans. (accepted).
Start Year 2014
 
Description Collaboration with the Prof Patrice Courvalin, Pasteur Institute, Paris 
Organisation Pasteur Institute, Paris
Country France 
Sector Charity/Non Profit 
PI Contribution A collaboration to explore the membrane protein components of antibiotic resistance machansism in bacteria was established in 2010
Start Year 2010
 
Description New collaboration (Patching) 
Organisation University of Leeds
Country United Kingdom 
Sector Academic/University 
PI Contribution A collaboration to explore NMR (solution and solid-state) spectroscopy as applied to membrane sensor kinases was established with Dr Simon G Patching (University of Leeds). This arose through the grant work which established that most membrane sensor kinases of E. faecalis can be purified as active intact proteins.
Collaborator Contribution Knowledge of NMR and CD
Impact Siligardi, G., Hussain, R., Patching, S.G. & Phillips-Jones, M.K. (2014). Ligand- and drug-binding studies of membrane proteins revealed through circular dichroism spectroscopy. Biochim. Biophys. Acta Biomembr. 1838: 34-42. (IF 3.919) Phillips-Jones, M.K., Patching, S.G., Edara, S., Nakayama, J., Hussain, R., & Siligardi, G. (2013). Investigation of the first step of a virulence regulatory pathway in a bacterial hospital-acquired infection agent. Diamond Light Source Annual Review 2012/13. pp30-31. Phillips-Jones, M.K., Patching, S.G., Edara, S., Nakayama, J., Hussain, R., & Siligardi, G. (2013) Interactions of the intact FsrC membrane histidine kinase with the tricyclic peptide siamycin I revealed through synchrotron radiation circular dichroism. Phys. Chem. Chem. Phys. 15, 444-447. (IF 3.829) Patching, S.G., Edara, S., Ma, P. Nakayama, J., Hussain, R., Siligardi, G. & Phillips-Jones, M.K. (2012) Interactions of the intact FsrC membrane histidine kinase with its pheromone ligand GBAP revealed through synchrotron radiation circular dichroism. Biochim. Biophys. Acta Biomembr. 1818, 1595-1602. (IF 3.919) (Highlighted in Diamond News 'A tale of two beamlines' Spring 2012). Patching, S.G., Middleton, D.A., Kalverda, A., Gowdy, J., Baldwin, S.A., Phillips-Jones, M.K., Levitt, M.H., Homans, S.W. & Henderson, P.J.F. (2012) NMR methods for structure-function investigation of membrane proteins and their ligands. J. Labell.Comp. Radiopharm. 55, 132-133. (IF 1.24)
Start Year 2010
 
Description New collaboration - Prof Margarida Archer at ITQB, Lisbon 
Organisation New University of Lisbon
Department António Xavier Institute of Chemical and Biological Technology
Country Portugal 
Sector Academic/University 
PI Contribution A new collaboration was established with ITQB, New University of Lisbon, Lisbon, Portugal
Start Year 2009
 
Description New collaboration with Japanese partner 
Organisation Kyushu University
Country Japan 
Sector Academic/University 
PI Contribution A new collaboration to work on FsrC was established with Professor Jiro Nakayama, Kyushu University, Japan.
Start Year 2008
 
Description Visit by International Authority (Prof Jiro Nakayama) 
Organisation Kyushu University
Country Japan 
Sector Academic/University 
PI Contribution A visit by Professor (Kyushu University, Japan) and presentation (Cyclic peptide quormone: A common communication tool in Gram-positive bacteria) to the Faculty of Biological Sciences, University of Leeds) on 08 January 2008.
Start Year 2008
 
Title Detection of bacterial infections 
Description Use of knowledge gained from the grant funding to detect bacterial infections 
IP Reference GB1406161.8 and GB1517300.8 
Protection Patent application published
Year Protection Granted 2014
Licensed No
Impact None aware of
 
Title Diagnostic test for detecting bacterial infections 
Description Diagnostic test for detecting bacterial infections. Under scientific feasibility development. Funded by an Innovation Grant from the University of Central Lancashire 
Type Diagnostic Tool - Non-Imaging
Current Stage Of Development Initial development
Year Development Stage Completed 2014
Development Status Under active development/distribution
Impact none known 
 
Description 1. Early publicity material upon elucidating the structure of the MhpI membrane protein 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Participants in your research or patient groups
Results and Impact Both Leeds and Imperial released publicity material when the structure of a transport protein Mhp1 (from other funding) appeared in Science. This resulted in at least the following articles/mentions in the media, including a telephone interview and report in a USA technical journal, all between 16-17 October, 2008, unless indicated otherwise.

Scientific Frontline www.sflorg.com



Physorg.com www.physorg.com

http://www.physorg.com/news143383612.html

Genetic Engineering News www.genengnews.com

http://www.genengnews.com/news/bnitem.aspx?name=43649828

Eureka Science News http://esciencenews.com

http://esciencenews.com/articles/2008/10/16/border.control.study.shows.how.proteins.permit.entry.a.cell

Science News Daily www.sciencenewsdaily.org

http://www.sciencenewsdaily.org/story-143383612.html

Individualall health news http://individualall.net

http://individualall.net/?p=849

Science Centric www.sciencecentric.com

http://www.sciencecentric.com/news/article.php?q=08101718

Cordis News (Belgium) http://cordiseuropa.eu

http://cordis.europa.eu/fetch?CALLER=EN_NEWS&ACTION=D&SESSION=&RCN=29995

Medical Geek www.medicalgeek.com

http://www.medicalgeek.com/articles/13306-study-shows-how-proteins-permit-entry-cell.html

eMax Health www.emaxhealth.com

http://www.emaxhealth.com/2/24/25495/how-proteins-permit-molecules-enter-cells.html

Nanotechnology Now www.nanotech-now.com

http://www.nanotech-now.com/news.cgi?story_id=31058

Scientific Blogging www.scientificbhlogging.com

http://www.scientificblogging.com/news_releases/cellular_border_patrol_how_proteins_control_what_gets_in

Science www.sciencemag.org

http://www.sciencemag.org/cgi/content/abstract/1164440

Medilexicon www.medilexicon.com

http://www.medilexicon.com/medicalnews.php?newsid=125909
Written material

no actual impacts realised to date
Year(s) Of Engagement Activity 2008
 
Description 2. Early publicity material upon elucidating the structure of the MhpI membrane protein 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Participants in your research or patient groups
Results and Impact Both Leeds and Imperial released publicity material when the structure of a transport protein Mhp1 (from other funding) appeared in Science. This resulted in at least the following articles/mentions in the media, including a telephone interview and report in a USA technical journal, all between 16-17 October, 2008, unless indicated otherwise.

(below is a continuation of the publicity material presented in Outcome: '1. Early publicity material upon elucidating the structure of the MhpI membrane protein'



Pharmaceutical Technology Europe www.ptemag.com

http://www.ptemag.com/pharmtecheurope/Online+Exclusives/Peter-Henderson-151-Crossing-cellboundaries/

ArticleStandard/Article/detail/560146?contextCategoryId=46689 (1/11/08)

Pharmaceutical Technology Europe Stephanie Sutton ssutton@advanstr.com.
Articles

no actual impacts realised to date
Year(s) Of Engagement Activity 2008
 
Description BBC Radio 4 'Material World' 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Media (as a channel to the public)
Results and Impact Peter Henderson participated in a BBC radio 4 programme 'Material world' hosted by Quentin Cooper in March, 2008.

no actual impacts realised to date
Year(s) Of Engagement Activity 2008
URL http://www.bbc.co.uk/programmes/profiles/49gDsDdvsRRP7G8nF5XYvly/quentin-cooper
 
Description Demonstration at Diamond Open Day (06/04/2013) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Type Of Presentation Poster Presentation
Geographic Reach local
Primary Audience Public/other audiences
Results and Impact Diamond Light Source Ltd Open Day - presentation of the grant's work performed collaboratively at the Diamond Light Source Ltd, to the public 06/04/2013. The demonstration describes the circular dichroism work performed using one of the sensor kinase proteins of the grant (FsrC) and the identification of an inhibitor that inhibits FsrC activity (interacting with FsrC as revelaed by the CD experiments), revealing the promise of the technique for identifying inhibitors of FsrC and therefore for disrupting biofilm formation (adherence to patient tissues/implants etc). There was also a demonstration of how to make a sucrose density gradient which the children enjoyed having a go at - illustrating how new science builds up from well-established scientific techniques. Two posters and a hands-on demonstration on how to pour a rainbow-coloured sucrose gradient.

no actual impacts realised to date
Year(s) Of Engagement Activity 2013
 
Description Diamond News -1 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? Yes
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Article on successful research outcomes reported in Spring 2012 edition of 'Diamond News' Spring 2012. A fuller account will also appear in the Autumn edition of the Diamond News. Although the grant finished in 2009 this work continues on from the grant and would not have been possible without the grant. Diamond News (Spring 2012) 'A tale of two beamlines'.

no actual impacts realised to date
Year(s) Of Engagement Activity 2012
URL http://www.diamond.ac.uk/Home/Corporate-Literature/newsletter/spring2012/two_beamline_B.html
 
Description Discovery Zone - science communicated to primary school children 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? Yes
Geographic Reach Regional
Primary Audience Schools
Results and Impact Demonstration exercises to primary school children from local schools in the Leeds and Bradford areas on DNA extraction and the nature of the DNA code. Materials being used within the grant period were used to help illustrate the exercise. A demonstration exercise involving letters that represent parts of the DNA code; extraction of DNA from natural sources using ethanol precipitation

no actual impacts realised to date
Year(s) Of Engagement Activity 2009