Annemarie Wehenkel

The structure of PknB in complex with mitoxantrone, an ATP-competitive inhibitor, suggests a mode of protein kinase regulation in mycobacteria

Mycobacterium tuberculosis PknB is an essential receptor‐like protein kinase involved in cell growth control. Here, we demonstrate that mitoxantrone, an anthraquinone derivative used in cancer therapy, is a PknB inhibitor capable of preventing mycobacterial growth. The structure of the complex reveals that mitoxantrone partially occupies the adenine‐binding pocket in PknB, providing a framework for the design of compounds with potential therapeutic applications. PknB crystallizes as a ‘back‐to‐back’ homodimer identical to those observed in other structures of PknB in complex with ATP analogs. This organization resembles that of the RNA‐dependent protein kinase PKR, suggesting a mechanism for kinase activation in mycobacteria.

The FHA-containing protein GarA acts as a phosphorylation-dependent molecular switch in mycobacterial signaling.

MINT‐6804218: GarA (uniprotkb:P64897) and GarA (uniprotkb:P64897) bind (MI:0407) by isothermal titration calorimetry (MI:0065)

The Crystal Structure of M. Leprae Ml2640C Defines a Large Family of Putative S-Adenosylmethionine- Dependent Methyltransferases in Mycobacteria.

Mycobacterium leprae protein ML2640c belongs to a large family of conserved hypothetical proteins predominantly found in mycobacteria, some of them predicted as putative S‐adenosylmethionine (AdoMet)‐dependent methyltransferases (MTase). As part of a Structural Genomics initiative on conserved hypothetical proteins in pathogenic mycobacteria, we have determined the structure of ML2640c in two distinct crystal forms. As expected, ML2640c has a typical MTase core domain and binds the methyl donor substrate AdoMet in a manner consistent with other known members of this structural family. The putative acceptor substrate‐binding site of ML2640c is a large internal cavity, mostly lined by aromatic and aliphatic side‐chain residues, suggesting that a lipid‐like molecule might be targeted for catalysis. A flap segment (residues 222–256), which isolates the binding site from the bulk solvent and is highly mobile in the crystal structures, could serve as a gateway to allow substrate entry and product release. The multiple sequence alignment of ML2640c‐like proteins revealed that the central α/β core and the AdoMet‐binding site are very well conserved within the family. However, the amino acid positions defining the binding site for the acceptor substrate display a higher variability, suggestive of distinct acceptor substrate specificities. The ML2640c crystal structures offer the first structural glimpses at this important family of mycobacterial proteins and lend strong support to their functional assignment as AdoMet‐dependent methyltransferases.

The crystal structure of the catalytic domain of the ser/thr kinase PknA from M. tuberculosis shows an Src‐like autoinhibited conformation

Signal transduction mediated by Ser/Thr phosphorylation in Mycobacterium tuberculosis has been intensively studied in the last years, as its genome harbors eleven genes coding for eukaryotic‐like Ser/Thr kinases. Here we describe the crystal structure and the autophosphorylation sites of the catalytic domain of PknA, one of two protein kinases essential for pathogens survival. The structure of the ligand‐free kinase domain shows an auto‐inhibited conformation similar to that observed in human Tyr kinases of the Src‐family. These results reinforce the high conservation of structural hallmarks and regulation mechanisms between prokaryotic and eukaryotic protein kinases. Proteins 2015; 83:982–988.

New substrates and interactors of the mycobacterial Serine/Threonine protein kinase PknG identified by a tailored interactomic approach

PknG from Mycobacterium tuberculosis is a multidomain Serine/Threonine protein kinase that regulates bacterial metabolism as well as the pathogens ability to survive inside the host by still uncertain mechanisms. To uncover PknG interactome we developed an affinity purification-mass spectrometry strategy to stepwise recover PknG substrates and interactors; and to identify those involving PknG autophosphorylated docking sites. We report a confident list of 7 new putative substrates and 66 direct or indirect partners indicating that PknG regulates many physiological processes, such as nitrogen and energy metabolism, cell wall synthesis and protein translation. GarA and the 50S ribosomal protein L13, two previously reported substrates of PknG, were recovered in our interactome. Comparative proteome analyses of wild type and pknG null mutant M. tuberculosis strains provided evidence that two kinase interactors, the FHA-domain containing protein GarA and the enzyme glutamine synthetase, are indeed endogenous substrates of PknG, stressing the role of this kinase in the regulation of nitrogen metabolism. Interestingly, a second FHA protein was identified as a PknG substrate. Our results show that PknG phosphorylates specific residues in both glutamine synthetase and FhaA in vitro, and suggest that these proteins are phosphorylated by PknG in living mycobacteria.