La tagatose-1,6-bisphosphate aldolase et la fructose-1,6-bisphosphate aldolase de classe I : mécanisme et stéréospécificité

La tagatose-1,6-biphosphate aldolase de Streptococcus pyogenes est une aldolase qui fait preuve d'un remarquable manque de spécificité vis à vis de ses substrats. En effet, elle catalyse le clivage réversible du tagatose-1,6-bisphosphate (TBP), mais également du fructose-1,6-bisphosphate (FBP), du sorbose-1,6-bisphosphate et du psicose-1,6-bisphosphate, quatre stéréoisomères, en dihydroxyacétone phosphate (DHAP) et en glycéraldéhyde-3-phosphate (G3P). Aldolase de classe I, qui donc catalyse sa réaction en formant un intermédiaire covalent obligatoire, ou base de Schiff, avec son susbtrat, la TBP aldolase de S. pyogenes partage 14 % d’identité avec l’enzyme modèle de cette famille, la FBP aldolase de muscle de mammifère. Bien que le mécanime catalytique de la FBP aldolase des mammifères ait été examiné en détails et qu’il soit approprié d’en tirer des renseignements quant à celui de la TBP aldolase, le manque singulier de stéréospécificité de cette dernière tant dans le sens du clivage que celui de la condensation n’est toujours pas éclairci. Afin de mettre à jour les caractéristiques du mécanisme enzymatique, une étude structurale de la TBP aldolase de S. pyogenes, un pathogène humain extrêmement versatile, a été entreprise. Elle a permis la résolution des structures de l’enzyme native et mutée, en complexe avec des subtrats et des inhibiteurs compétitifs, à des résolutions comprises entre 1.8 Å et 2.5 Å. Le trempage des cristaux de TBP aldolase native et mutante dans une solution saturante de FBP ou TBP a en outre permis de piéger un authentique intermédiaire covalent lié à la Lys205, la lysine catalytique. La determination des profils pH de la TBP aldolase native et mutée, entreprise afin d'évaluer l’influence du pH sur la réaction de clivage du FBP et TBP et ìdentifier le(s) résidu(s) impliqué(s), en conjonction avec les données structurales apportées par la cristallographie, ont permis d’identifier sans équivoque Glu163 comme résidu responsable du clivage. En effet, le mode de liaison sensiblement différent des ligands utilisés selon la stéréochimie en leur C3 et C4 permet à Glu163, équivalent à Glu187 dans la FBP aldolase de classe I, d’abstraire le proton sur l’hydroxyle du C4 et ainsi d’amorcer le clivage du lien C3-C4. L’étude du mécanimse inverse, celui de la condensation, grâce par exemple à la structure de l’enzyme native en complexe avec ses substrats à trois carbones le DHAP et le G3P, a en outre permis d’identifier un isomérisme du substrat G3P comme possible cause de la synthèse des isomères en C4 par cette enzyme. Ce résultat, ainsi que la decouverte d’un possible isomérisme cis-trans autour du lien C2-C3 de la base de Schiff formée avec le DHAP, identifié précedemment, permet de cerner presque complètement les particularités du mécanisme de cette enzyme et d’expliquer comment elle est capable de synthétiser les quatres stéréoisomères 3(S/R), 4(S/R). De plus, la résolution de ces structures a permis de mettre en évidence trois régions très mobiles de la protéine, ce qui pourrait être relié au rôle postulé de son isozyme chez S. pyogenes dans la régulation de l’expression génétique et de la virulence de la bactérie. Enfin, la résolution de la structure du mutant Lys229→Met de la FBP aldolase de muscle en complexe avec la forme cyclique du FBP, de même que des études cristallographiques sur le mutant équivalent Lys205→Met de la TBP aldolase de S. pyogenes et des expériences de calorimétrie ont permis d’identifier deux résidus particuliers, Ala31 et Asp33 chez la FBP aldolase, comme possible cause de la discrimination de cette enzyme contre les substrats 3(R) et 4(S), et ce par encombrement stérique des substrats cycliques. La cristallographie par rayons X et la cinétique enzymatique ont ainsi permis d'avancer dans l'élucidation du mécanisme et des propriétés structurales de cette enzyme aux caractéristiques particulières.

Mass Surveillance of Personal Data by EU Member States and its Compatibility with EU Law. CEPS Liberty and Security in Europe No. 61, 6 November 2013

In the wake of the disclosures surrounding PRISM and other US surveillance programmes, this paper assesses the large-scale surveillance practices by a selection of EU member states: the UK, Sweden, France, Germany and the Netherlands. Given the large-scale nature of these practices, which represent a reconfiguration of traditional intelligence gathering, the paper contends that an analysis of European surveillance programmes cannot be reduced to a question of the balance between data protection versus national security, but has to be framed in terms of collective freedoms and democracy. It finds that four of the five EU member states selected for in-depth examination are engaging in some form of large-scale interception and surveillance of communication data, and identifies parallels and discrepancies between these programmes and the NSA-run operations. The paper argues that these programmes do not stand outside the realm of EU intervention but can be analysed from an EU law perspective via i) an understanding of national security in a democratic rule of law framework where fundamental human rights and judicial oversight constitute key norms; ii) the risks posed to the internal security of the Union as a whole as well as the privacy of EU citizens as data owners and iii) the potential spillover into the activities and responsibilities of EU agencies. The paper then presents a set of policy recommendations to the European Parliament.

Carbon leakage: an overview. CEPS Special Report No. 79, 6 December 2013

Carbon leakage is central to the discussion on climate policy, given the confluence of issues that are currently being debated, including the 2030 Energy and Climate Framework and the review of the EU carbon leakage list by 2014. Carbon leakage is the result of asymmetrical carbon policies, especially carbon pricing, and the resulting carbon cost, which affects the international competitive position of some EU industry and could displace production and/or investment, and the emissions of the activities displaced. This paper identifies the difference between carbon price and carbon cost to leakage exposed industry as one of two fundamental issues to be understood and addressed; lack of visibility on future climate policies and anti-leakage provisions is the other key issue. While this is a global issue, most of the experience has been accumulated in the EU. Carbon leakage is only one of the factors that could affect the competitive position of sectors, but it is difficult to attribute the impact of carbon costs versus other variables such as energy costs, labour, etc. Studies have predicted the risk of a significant amount of production leakage in a number of energy-intensive industries. To address the danger, they were included in the EU ETS carbon leakage list, which gave them access to free allowances. However, a limited number of studies undertaken after the end of the second trading period (2012) show little evidence of production leakage and asks the question whether the issue has not been blown out of proportion. The paper argues that the past may not be a good representation of the future, as it was heavily influenced by a high level of free allocation, the exceptional economic downturn, CO2 prices significantly below what was anticipated, as well as the potential for changes in some fundamental variables such as the shrinking pool of allowances available for free allocation. It emphasises the need for a well-informed debate in the EU on measures to address carbon leakage post-2020, underpinned by a number of options, and objective criteria to evaluate those options. It emphasises that the debate should cover both investment and production leakage, caused by both direct and indirect carbon costs.

Unblocking the Lifeline of Talent. CEPS Policy Brief No. 306, 6 December 2013

Against the background of looming demographic decline, the departure of the baby-boom generation from European labour markets and growing economic competitiveness from emerging economies, this CEPS Policy Brief, published jointly with the Bertelsmann Stiftung, looks into the potential benefits of increased intra-EU labour mobility. The authors examine the ‘German case’ on EU labour mobility, digging below the surface of the aggregate data. They offer proposals on how to foster a European fair deal on talent, one that would benefit the EU as a whole. The paper concludes with policy recommendations on how to increase the potential benefits of the freedom of movement for both individual EU citizens and for the EU as a whole.

The New EU Climate and Energy Package: Passing the test? CEPS Commentary, 6 January 2014

On 22 January 2014, the European Commission is expected to publish the proposals for the 2030 Framework for Climate and Energy Policies, which will be discussed and possibly – or maybe, partly – agreed during the 20-21 March 2014 European Council. This is the first comprehensive review of the 2007-09 Climate and Energy Package, which resulted in the so-called ‘20-20-20’ targets by 2020. The principal intention is to define the EU’s climate change and energy policy framework for the next decade and beyond to give investors an adequate amount of predictability if not certainty. This Commentary argues, however, that the ‘2030 Framework’ is not just about predictability; it is also about making the proper adjustments based on the lessons learned and also in response to new issues that have emerged in the interim. The authors ask what the main lessons are and how they should influence the 2030 Framework. Or put differently, what are the conditions that the “2030 Framework” will need to meet in order to offer a viable package for discussion?

The European Elections in France: The paradox of a more European yet more eurosceptic campaign. EPIN Commentaries No. 16, 6 February 2014

Despite the probable shift towards European rather than national issues in the European election campaign in France, the combined effects of the economic crisis and the unpopularity of political leaders could crystallise a ‘protest’ vote for both national and European leaders, and for the EU as a whole, explain the authors in this EPIN Commentary.

Europe is still standing. CEPS Commentary, 6 June 2014

Despite the fact that anti-establishment, mostly euro-sceptic parties won about one-fifth of the vote in the European Parliament elections last month, Daniel Gros insists that it is not quite accurate (or fair) to characterise the result as a rejection of Europe. He argues that the deeper roots of the surge of euro-sceptic and other protest parties originate with the general dissatisfaction with the state of the economy and dysfunctional national political systems. Tinkering with austerity or the fundamental right of free movement within the EU will not make much of a difference and, in his view, only reform at home, in national capitals, will stem the tide of euro-scepticism.

Never mind the Spitzenkandidaten: It's all about politics. CEPS Commentary, 6 June 2014

In this new commentary, CEPS Fellow Marco Incerti argues that the so-called technical and legal arguments that are being advanced against the lead candidates’ (Spitzenkandidaten) selection process actually boil down to political choices − choices that are set against the increasingly confrontational climate between the European Council and European Parliament that has characterised their dealings in recent years.

Moldova – Heading into a hot autumn. EPC Policy Brief, 6 October 2014

After four years of negotiations, Moldova signed an Association Agreement (AA) including a Deep and Comprehensive Free Trade Area (DCFTA) Agreement with the European Union (EU) on 27 June 2014. Ratified in the Moldovan Parliament on 2 July it came into provisional application on 1 September. While this development represents an important milestone in Moldova’s relations with the EU, the journey has not been easy. Russia has increased its presence and pressure in the region, as the country gets closer to bettering relations with the EU, Russia has increased its activities in Moldova, including in the autonomous region of Gagauzia and in the breakaway region of Transnistria. Alongside pressure from Russia, the next few months will be very politically challenging for Moldova, with internal and external developments continuing to shape Moldova’s future. Not only will Chisinau need to move ahead with the difficult and expensive implementation of the DCFTA, the ruling coalition simultaneously needs to campaign for the elections with very importantly, a united front. In this Policy Brief, Amanda Paul presents the state of play and the prospects of Moldova since signing the Association Agreement with the EU and explores the effects of Russian bans on exports and services, access to energy and trade as well as the role of the EU

The future of human rights protection in the new Libya: prospects and challenges. Jean Monnet Occasional Paper No. 6/2014

There is no doubt that demand for the respect of human rights was one of the factors behind the Arab Spring and Libya is no exception. Four decades of absolute dictatorship headed by Muammar Gaddafi had been further tainted with gross violations of human rights of Libyan citizens and restrictions on their basic freedoms. Before the revolution, Libya was a country where no political parties were allowed. Freedom of expression and the press were extremely restricted. Reports about the country’s human rights violations published by a number of international organizations documented large scale human rights abuses at the hands of the Gaddafi regime. The 17 February 2011 revolution in Libya led to a turning point in the country’s history. The regime of Muammar Gaddafi which had dominated the country since 1969 eventually collapsed, leading to the beginning of the painful task of reconciliation and state building. Nonetheless it is estimated that more than 7000 prisoners are held captive by various militias and armed groups without due process. This in addition to thousands of internally displaced persons. State building involves the consolidation of a democratic state based on a democratic constitution. In 2011, a constitutional declaration was adopted to replace the one that had been in effect since 1969. This was intended as a stop-gap solution to allow the new political forces unleashed in the country time to write a new democratic constitution. To help consolidate the democratic state, three elements are required: that human rights be placed at its core; that these rights are truly implemented and applied; and lastly that the independence of the judiciary is safeguarded. For all this to happen it is also essential to strengthen education on human rights by encouraging non-governmental organizations to take a stronger role in promoting human rights. Libyan citizens can only avail themselves of these rights and strengthen their implementation if they know what they are and how they can benefit from their implementation

Perspectives in Resource Management and Climate Change Adaptation in the Southern and Eastern Mediterranean. MEDPRO Policy Paper No. 6, March 2013

This policy paper focuses on the sustainable management of some key natural resources in southern and eastern Mediterranean countries (SEMCs) under climate change and anthropogenic pressures. In a business-as-usual and even more so in a failed cooperation scenario, water resources, ecosystems and biodiversity in the region are under stress, with negative consequences for agriculture, food security, tourism and development. However, proper adaptation strategies are shown to be effective in reconciling resource conservation with GDP, trade and population growth. These need be implemented in different ways: technological, institutional, behavioural; and at different levels: regional, national and international. There is ample room for fruitful cooperation between the EU and SEMCs in this area, which can take the form of EU direct financial and technical support when resources in SEMCs are scarce, and of multilateral and bilateral cooperation programmes to improve resource efficiency. The EU could also take on the role of coordinating these different bilateral actions and, at the same time, support SEMCs to establish a structured programme focused on the communication and dissemination of emerging best practices.

The 2005 Reform of the Stability and Growth Pact: Too Little, Too Late? Bruges European Economic Research (BEER) Papers 6/November 2006

This paper analyses the main critiques addressed by the literature and the policymakers to the 1997 Stability and Growth Pact. It further indicates to what extent the 2005 reform of the Pact meets those critics. It finally argues that the 2005 reform may be too little and arrive too late to restore the Pact credibility, ensure its enforceability and correctly set the derogations to the excessive deficit procedure on the nature of the shocks which cause the output gap rather than its size: a 3% of GDP limit on deficit spending may be a too binding constraint in front of a strongly negative demand shock, while it is irrationally large in front of a supply shock. Some empirical evidence is provided to identify in the last years strongly negative demand shocks from other shocks in the 25 EU Member States. Had this identifying method been adopted in November 2003, the European Commission and the Council would have both agreed to stop the excessive deficit procedure against Germany, but they would have both proceeded against France which apparently was not at the time hit by a strongly negative demand shock.

The ICC Debate and the EU-U.S. Struggle for Influence: The Case of the Balkan-6. ACES Working Paper No. 11, October 2007

The objectives of the European Union (EU) and the United States (US) for the countries of the Balkan region are generally assumed to be complementary. They both stress and condition their support and assistance on the progress that these countries make with regards to economic modernization, build-up of social institutions, and respect for international law. However, this rhetoric doesn't always match the facts on the ground. Often, instead of dealing with a cohesive set of policy recommendations, the countries in the region are faced with contradictory alternatives and zero-sum choices. The debate over the development of the International Criminal Court (ICC) was such a case. It centered on whether the countries in the region should exempt US personnel from the jurisdiction of the Court while in the country and thus rendering them immune from prosecution for any crimes committed for which the US courts were not willing or able to take any action. The final outcome was mixed. Three of the countries - Croatia, Serbia (and Montenegro), and Slovenia - decided not to give in to US pressure, while the remaining three - Albania, Bosnia and Herzegovina, and Macedonia - ignored the pleas and threats of the EU and of the various international non-governmental organizations and decided to sign Bilateral Immunity Agreements (BIAs) with the US. How can one explain such divergent outcomes? I argue that the credibility of actors involved played an important role in determining whether threats coming from the US or the EU were more credible, thus tipping the scales in favor of signing BIAs with the US. However, the issue of threat credibility serves only to narrow down the choices of actors. Further determination of the outcome necessitates a look at the nature of the security context in which these countries exist and operate.

West African Migrants in Spain: Human Factors and Emerging International Policy. ACES Working Paper No. 6, Fall 2008

This paper concerns itself with the recent phenomenon of West Africans leaving the African continent and seeking work in Spain. By the year 2003, a barely noticeable blip on the screen of the age-old phenomenon that is migration became a conspicuous trend. Depending on one's perspective this trend is either a natural flow of people from one region to another, or it is an alarming turn of events that needs immediate global attention. However, when it involves significant loss of life - as does the sea journey of the poorest aspirants - surely all who ponder the migrant question would agree that this qualifies as a crisis. The next question becomes, then, is it best to focus on minimizing the risks or to focus on deterring the would-be migrants at the onset of their journey? This question and its possible answer are further nuanced by whether those determined to leave receive incentives for choosing to stay at home or whether government officials and others who respond to the crisis in both sending and receiving countries practice a forceful type of deterrent that merely halts the process of migration but does not tackle the issue of why the person chose to leave in the first place.

Syria and Lebanon: Diverging paths of state unsustainability. MEDPRO Technical Report No. 6/June 2011

Any analysis of the prospects for stability and sustainability in the states of Syria and Lebanon reveals the strong ties that exist between these two countries and the impact of external influences on their overall development. Their trajectories, while starkly divergent in terms of the challenges confronting them at present, converge on a path of long-term unsustainability. Lebanon is in the midst of yet another transition phase, triggered by the collapse of Hariri’s government in January 2011. The current situation might be described as one of deteriorating status quo; the state is performing poorly in terms of its delivery of fundamental public services and its institutional legitimacy is tenuous in the face of emerging para-state structures and latent (occasionally active) violence. In Syria, challenges to the sustainability of the state have evolved dramatically since the beginning of 2011, and are now nearing a tipping point. In view of the mounting unrest and violence in the country, the future prospects for its economic and political development are dim. More ominously, the risk of widespread conflict, with sectarian overtones, cannot be discounted.