Sulfido dithiolene complexes modeling molybdenum and tungsten dependent oxiodreductases - investigating synthesis, catalysis and biological activity to elucidate structural uncertainties, structure-function relationships and biosynthesis

铁-硫团簇对必需的钼和钨氧化还原酶的生物合成和功能至关重要。钼和钨辅助因子的成熟和催化活性将被研究的关键方面，直接依赖于FeS簇蛋白(关键词：串扰)。通过化学模型合成、光谱表征、催化和动力学评估以及与蛋白质(伴侣/脱辅酶)的生物相互作用，将有助于更好地了解各种酶及其协同作用。重要的问题特别涉及硫化配体在钼和钨活性部位的作用，这是由ISCS在体内引入/转移的。硫磺配位及其对酶反应活性的作用将在模型化合物上进行化学研究。将阐明催化机制，并使用所有分析结果适当地区分该硫化物配体在各自酶的活性部位的实际存在和人为存在(在某些情况下，它的存在并不明确)。选择性地用同位素标记模型络合物中的硫磺配体将进一步加深各自所需的洞察力。最近被证明能诱导与天然蛋白质结合的高度发达的配体系统，将在这一背景下产生重大影响，并进一步了解细胞过程；特别是硫的转移和插入，这与二硫杂环戊烯(MPT)配体和硫化物配位特别相关。复杂的钼(钨)单氧双二硫烯络合物模拟天然MPT的各个方面，应通过交换硫化物(=S)进行氧化(=O)连接来进行修饰，为此，应用双羰基前体被确定为最可行的步骤。为合成MVIOS物种，将研究电化学氧化和SH-离子的伴随存在。叠氮二硫代钼配合物的合成是另一个重要的目标。通过比较酶和模型络合物的光谱数据，需要这些络合物来阐明依赖钼的大肠杆菌甲酸脱氢酶(FDH)的抑制作用。叠氮与蛋白质的结合是与酶产物二氧化碳等电子的，这将有助于理解FDH的反应机理，这也对CO2化学有意义。对所有合成的配合物进行光谱综合表征，研究它们的催化潜力和此类反应的动力学，并研究它们的生物活性，将有助于深入了解自然界促进反应性和伴随稳定性的策略。生物活性将通过研究与参与钼或钨辅助因子成熟的蛋白质以及脱辅酶和各自的半合成酶的催化活性的特异性结合来评估。

Iron-sulfur cluster are critically important for the biosynthesis and function of essential molybdenum and tungsten oxidoreductases. Crucial aspects will be investigated of the maturation and catalytic activity of molybdenum and tungsten co-factors, being directly dependent on FeS cluster proteins (keyword: crosstalk). A better understanding of the respective enzymes and their synergy shall be facilitated by chemical model syntheses, spectroscopic characterization, catalytic and kinetic evaluation and the biological interaction with proteins (chaperones/apo-enzymes). Important issues specifically concern the role of the sulfido ligand in the Mo and W active sites, which is introduced/transferred in vivo by IscS. Sulfido coordination and its function for the enzymes’ reactivity in particular, will be chemically studied on model compounds. The catalytic mechanisms will be elucidated and all analytical results used to competently discriminate between actual and artefactual presence of this sulfido ligand in the active sites of respective enzymes (in some of which its presence being not unambiguously clear). Isotopically labelling the sulfido ligand in model complexes selectively will further the respective required insight. Highly developed ligand systems, having recently been shown to induce binding to natural proteins, will have significant impact in this context and further the understanding of cellular processes; in particular of sulfur transfer and insertion, which is specifically relevant for the dithiolene-derived molybdopterin (MPT) ligands and sulfido coordination. Sophisticated mono-oxido bis-dithiolene complexes of molybdenum (and tungsten), mimicking various aspects of natural MPT, shall be modified by exchanging sulfido (=S) for oxido (=O) ligation for which the application of bis-carbonyl precursors was established as the most feasible procedure. Electrochemical oxidation and the concomitant presence of SH– ions will be investigated for the synthesis of MVIOS species. The synthesis of azide dithiolene molybdenum complexes constitutes another important aim. Such complexes are needed for elucidating the inhibition of Mo-dependent E. coli formate dehydrogenase (FDH) by comparison of enzymatic and model complex spectroscopic data. Being isoelectronic to the enzymatic product CO2, azide binding to protein will serve the understanding of FDH’s reaction mechanism, which again has implications for CO2 chemistry. Comprehensively characterising all synthesised complexes spectroscopically, studying their catalytic potential and the kinetics of such reactions plus investigating their biological activity will provide intimate insight into nature’s strategies to foster reactivity and concomitant stability. The biological activity will be assessed by investigating specific binding to proteins, which participate in molybdenum or tungsten cofactor maturation, as well as to apoenzymes and the catalytic activity of respective semi-synthetic enzymes.