Browsing by Author "Holger, Gohlke"
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Item Movie for: The architecture of the 10-23 DNAzyme and its implications for DNA-mediated catalysis(N/A, 2022-09-19) Christoph, Gertzen; Jan, Borggräfe; Aldino, Viegas; Manuel, Etzkorn; Holger, GohlkeUnderstanding the molecular features of catalytically active DNA sequences, so-called DNAzymes, is not only essential for our understanding of the fundamental properties of catalytic nucleic acids in general but may well be the key to unraveling their full potential via tailored modifications. Our recent findings contributed to the endeavor to assemble a mechanistic picture of DNA-mediated catalysis by providing high-resolution structural insights into the 10-23 DNAzyme (Dz) and exposing a complex interplay between the Dz´s unique molecular architecture, conformational plasticity, and dynamic modulation by metal ions as central elements of the DNA catalyst. To illustrate the sampled conformational space, the movie depicts one MD trajectory of the Dz:RNA complex.Item Structural and mechanistic insights into bacterial phospholipase A involved in membrane phospholipid degradation and virulence(N/A, 2022) Stephan, Schott-Verdugo; Holger, Gohlke; Renu, Batra-Safferling; Karl-Erich, Jaeger; Filip, KovacicCells steadily adapt their membrane glycerophospholipid (GPL) composition to changing environmental and developmental conditions. While the regulation of membrane homeostasis via GPL synthesis in bacteria has been studied in detail, the mechanisms underlying the controlled degradation of endogenous GPLs remain unknown. Thus far, the function of intracellular phospholipases A (PLAs) in GPL remodeling (Lands cycle) in bacteria is not clearly established. Here, we identified the first cytoplasmic membrane-bound phospholipase A1 (PlaF) from Pseudomonas aeruginosa, which might be involved in the Lands cycle. PlaF is an important virulence factor, as the P. aeruginosa ΔplaF mutant showed strongly attenuated virulence in Galleria mellonella and macrophages. We present a 2.0-Å-resolution crystal structure of PlaF, the first structure that reveals homodimerization of a single-pass transmembrane (TM) full-length protein. PlaF dimerization, mediated solely through the intermolecular interactions of TM and juxtamembrane regions, inhibits its activity. The dimerization site and the catalytic sites are linked by an intricate ligand-mediated interaction network, which might explain the product (fatty acid) feedback inhibition observed with the purified PlaF protein. We used molecular dynamics simulations and configurational free energy computations to suggest a model of PlaF activation through a coupled monomerization and tilting of the monomer in the membrane, which constrains the active site cavity into contact with the GPL substrates. Thus, these data indicate the importance of the PlaF mediated GPL remodeling pathway for virulence and could pave the way for the development of novel therapeutics targeting PlaF.Item TopEnzyme: A framework and database for structural coverage of the functional enzyme space(N/A, 2022-12) Karel, van der Weg; Holger, GohlkeTopEnzyme is a database of structural enzyme models created with TopModel and is linked to the SWISS-MODEL repository and AlphaFold Protein Structure Database to provide an overview of structural coverage of the functional enzyme space for over 200,000 enzyme models. It allows the user to quickly obtain representative structural models for 60% of all known enzyme functions. We assessed the models with TopScore and contributed 9039 good-quality and 1297 high-quality structures. Furthermore, we compared these models to AlphaFold2 models with TopScore and found that the TopScore differs only by 0.04 on average in favor of AlphaFold2. We tested TopModel and AlphaFold2 for targets not seen in the respective training databases and found that both methods create qualitatively similar structures. When no experimental structures are available, this database will facilitate quick access to structural models across the currently most extensive structural coverage of the functional enzyme space within Swiss-Prot.Item Uncoupling of voltage- and ligand-induced activation in HCN2 channels by glycine inserts(N/A, 2022) Sezin, Yüksel; Michele, Bonus; Christopher, Pfleger; Holger, Gohlke; Klaus, Benndorf; Jana, KuschHyperpolarization-activated cyclic nucleotide-modulated (HCN) channels are tetramers that generate electrical rhythmicity in special brain neurons and cardiomyocytes. The channels are activated by membrane hyperpolarization. The binding of cAMP to the four available cyclic nucleotide-binding domains (CNBD) enhances channel activation. We analyzed in the present study the mechanism of how the effect of cAMP binding is transmitted to the pore domain (PD). Our strategy was to uncouple the C-linker (CL) from the channel core by inserting one to five glycine residues between the S6 gate and the A’-helix (constructs 1G to 5G). We quantified in full-length HCN2 channels the resulting functional effects of the inserted glycines by current activation as well as the structural dynamics and statics using molecular dynamics simulations and Constraint Network Analysis (CNA). We show functionally that already in 1G the cAMP effect on activation is lost and that with the exception of 3G and 5G the concentration-activation relationships are shifted to depolarized voltages with respect to HCN2. The strongest effect was found for 4G. Accordingly, the activation kinetics were accelerated by all constructs, again with the strongest effect in 4G. The simulations reveal that the average residue mobility of the CL and CNBD domains is increased in all constructs and that the junction between the S6 and A’-helix is turned into a flexible hinge, resulting in a destabilized gate in all constructs. Moreover, for 3G and 4G, there is a stronger downward displacement of the CL-CNBD than in HCN2 and the other constructs, resulting in an increased kink angle between S6 and A’-helix, which in turn loosens contacts between the S4-helix and the CL. This is suggested to promote a downward movement of the S4-helix, similar to the effect of hyperpolarization. In addition, exclusively in 4G, the selectivity filter in the upper pore region and parts of the S4-helix are destabilized. The results provide new insights into the intricate activation of HCN2 channels.