Pyruvate kinase catalyses the final step in glycolysis and is responsible for net ATP production. There are four pyruvate kinase isoforms expressed in humans; LPYK, RPYK, M1PYK and M2PYK. The allosteric enzyme M2PYK plays an important role in cancer cell metabolism and is subject to complex regulation by numerous naturally occurring small-molecule metabolites. Post-translational modifications have also been found to play a key role in the regulation of M2PYK, among these cysteine oxidation. This thesis describes the production and characterisation of M2PYK cysteine point mutants in order to investigate the mechanism of regulation by cysteine modification. From a total of ten cysteines present in M2PYK, five were chosen for mutation based on a combination of the results from the cysteine oxidation prediction program (COPP) web interface and published experimental evidence for cysteine modification of M2PYK. Eight point mutants of these five cysteines were produced and characterised. Low resolution gel filtration of all the mutants shows that mutation of these cysteines has an effect on tetramer:dimer:monomer equilibrium of M2PYK suggesting that cysteine modifications could regulate M2PYK activity by affecting oligomeric state. Activity assays show that none of the cysteine point mutations are sufficient to protect M2PYK from oxidation by H2O2 indicating that more than one cysteine is involved in the regulation of M2PYK by oxidation. Nitric oxide (NO) imbalance has recently emerged as playing a key role in numerous diseases including cancer. NO regulates the function of target proteins through the addition of a nitroso moiety from NO-derived metabolites to a reactive cysteine, a process known as protein S-nitrosylation. M2PYK has been found to be S-nitrosylated in vivo. Using the biotin-switch assay in vitro combined with mass spectrometry I have shown that a likely candidate for the target of S-nitrosylation of M2PYK is C326. This thesis also describes the structures of two cysteine point mutants; M2PYK C424A and M2PYK C358S. The structures show that these mutations have very little effect on the overall conformation of M2PYK with only very subtle localised changes. The structure of the mutant M2PYK C358S shows some interesting features including varying occupation of the active site resulting in differing conformations of the B domains within the same tetramer, and an unusual B factor distribution which could be indicative of a perturbation in cooperativity within the tetramer caused by the mutation.

The work describes the development of a new class of protein-inhibitors for protein-protein interactions, based on metallopeptides comprised of a dirhodium metal center. The metal incorporation in the peptide sequence leads to high increase in binding affinity of the inhibitors. The source of this strong affinity is the interaction of histidine on the protein surface with the rhodium center. In addition to this work, rhodium-based small molecule inhibitors for FK-506 binding proteins are investigated. Also, methodology for rhodium-catalyzed modification of proteins containing surface cysteine has been developed where a simple rhodium(II) complex catalyzes cysteine modification with diazo reagents. The reaction is marked by clean cysteine selectivity and mild reaction conditions. The resulting linkage is significantly more stable in human plasma serum, when compared to common maleimide reagents. Apart from this body of work in chemical-biology, the thesis contains the discussion of development of copper-catalyzed remote chlorination of alkyl hydroperoxides. The atom transfer chlorination utilizes simple ammonium chloride salts as the chlorine source and the internal redox process requires no external redox reagents.

In der vorliegenden Arbeit wird eine modulare Reaktionssequenz von zwei aufeinanderfolgenden chemoselektiven Umwandlungen vorgestellt: Es wird gezeigt, dass Vinyl- und Ethynylphosphonamidate chemoselektiv mit Cysteinen von Proteinen und Antikörpern reagieren. Weiterhin wird gezeigt, dass elektrophile Phosphonamidate durch eine vorhergehende chemoselektive Staudinger-Phosphonit Reaktion zwischen Aziden und ungesättigten Phosphoniten in das gewünschte Molekül eingebaut werden können. Hierbei wird ein elektronenreiches Phosphonit in ein elektronenarmes Phosphonamidat umgewandelt, welches somit für die nachfolgende Thiol-Addition aktiviert wird. Die beschriebene Methode erweitert das bestehende Repertoire von Biokonjugationen durch die Einführung eines neuen Konzepts: Eine chemoleselektive Reaktion, die Reaktivität für eine nachfolgende Biokonjugation induziert. Da Phosphonamidat-Konjugationen an Cysteine herausragende Eigenschaften, wie hohe Selektivität für Cysteine, saubere Reaktionsprodukte und eine hervorragende Stabilität mitbringen, wird im zweiten Teil beschrieben wie Phosphonamidate für die Anbindung von zytotoxischen Wirkstoffen an tumor-bindende Antikörper genutzt werden können um Antikörper-Wirkstoff-Konjugate (ADCs) herzustellen. Ein einfaches Syntheseprotokoll für die Herstellung, ausgehend von einem nicht gentechnisch veränderten Antikörper mit nur geringen Überschüssen des Wirkstoffs wird vorgestellt. Phosphonamidat-verbundene ADCs zeigen im direkten Vergleichen zum zugelassenen, Maleimid-verbundenen Adcetris überlegende Eigenschaften, wie eine erhöhte Stabilität in Serum und eine erhöhte in vivo Wirksamkeit in einem Tumor Mausmodel. Zusammenfassend verbindet die hier vorgestellte Methode einen einfachen synthetischen Zugang mit hoher Selektivität, überragender Konjugat-Stabilität und der Möglichkeit hochwirksame Wirkstoffkonjugate herzustellen und wird daher aller Voraussicht nach einen großen Beitrag zum Gebiet der zielgerichteten Therapie leisten. / The present work introduces a modular reaction sequence of two chemoselective manipulations in a row. It is shown that vinyl- and ethynylphosphonamidates react selectively with cysteine residues on proteins and antibodies. Most importantly, those electrophilic phosphonamidates can be incorporated into a given molecule in another preceding chemoselective Staudinger-phosphonite reaction (SPhR) from unsaturated phosphonites and azides. During this reaction, an electron-rich phosphonite is transformed into an electron-deficient phosphonamidate that is thereby activated for the subsequent thiol addition. The described technique thereby extends the existing repertoire of bioconjugations by introducing a new concept in protein synthesis: A chemoselective reaction that induces reactivity for a subsequent bioconjugation. Since phosphonamidate conjugations to cysteine hold outstanding features such as high selectivity for cysteine, clean reaction products and excellent stability of the protein adducts in biological environments, it is described in the second part of the present work how ethynylphosphonamidates can be employed for the conjunction of tumor-sensing antibodies and cytotoxic drugs to generate Antibody-Drug-Conjugates (ADCs). A simple synthetic protocol starting from unengineered antibodies, using only a slight excess of the desired drug in a one-pot synthesis protocol is introduced. In a direct comparison to the maleimide containing FDA-approved Adcetris, phosphonamidate linked ADCs show a superior behaviour in terms of linkage stability in serum, combined with an increased in vivo efficacy in a tumor xenograft mouse model. Taken together, the method described herein combines simple synthetic access with high selectivity, superior conjugate stability and the possibility to synthesize highly efficacious drug conjugates and is therefore likely to have a great contribution to the field of targeted therapeutics.