Biology subjects

Schiott, B.

Publications and source records attributed to Schiott, B..

3 recordsLinked to original sources

bioRxiv2020

Beneficent and maleficent effects of cations on bufadienolide binding to Na+,K+-ATPase

Kinetic properties and crystal structures of the Na+,K+-ATPase in complex with cardiotonic steroids (CTS) revealed significant differences between CTS subfamilies (Laursen et al., 2015): beneficial effects of K+ on bufadienolide binding strongly contrasted with K+/cardenolide antagonism. To solve this riddle we applied docking and molecular dynamics simulations of the complexes involving Na+,K+-ATPase, bufadienolides (bufalin, cinobufagin), and ions (K+, Na+, Mg2+). The results revealed that bufadienolide binding is affected by i) electrostatic attraction of the lactone ring by a cation, and ii) the ability of a cation to stabilize and "shape" the site constituted by transmembrane helices of the -subunit (M1-6). The latter effect was due to varying coordination patterns involving amino acid residues from helix bundles M1-4 and M5-10. Substituents on the steroid core of a bufadienolide add to and modify the cation effects. The above rationale is fully consistent with the ion effects on the kinetics of Na+,K+-ATPase/bufadienolide interactions.

biophysics↗

bioRxiv2020

Molecular mechanism of high affinity sugar transport in plants unveiled by structures of glucose/H+ symporter STP10

Sugars are essential sources of energy and carbon, and also function as key signaling molecules in plants. Sugar Transport Proteins (STP) are proton-coupled symporters, solely responsible for uptake of glucose from the apoplastic compartment into cells in all plant tissues. They are integral to organ development in symplastically isolated tissues such as seeds, pollen and fruit. Additionally, STPs play a significant role in plant responses to both environmental stressors such as dehydration, and prevalent fungal infections like rust and mildew. Here, we present two high-resolution crystal structures of the outward-occluded and inward-open conformations of Arabidopsis thaliana STP10 with glucose and protons bound. The two structures describe key states in the STP transport cycle. Together with in vivo biochemical analysis and Molecular Dynamics simulations they pinpoint structural elements that explain how STPs exhibit high affinity for sugar binding on the extracellular side and how it is considerably lowered on the intracellular side to facilitate substrate release. These structural elements, conserved in all STPs across plant species, clarify the basis of proton-to-glucose coupling, essential for symport. The results advance our understanding of a key molecular mechanism behind plant organ development, and sets the stage for novel bioengineering strategies in crops that could target seeds, fruits and plant resistance to fungal infections.

plant biology↗

bioRxiv2020

Substrate Recognition by γ-Glutamyltransferase: A Molecular Dynamics Simulations Study

{gamma}-glutamyltransferase (GGT) is an enzyme that uses {gamma}-glutamyl compounds as substrate and catalyzes their transfer into a water molecule or an acceptor substrate with varied physiological-function in bacteria, plants and animals. Crystal structures of GGT are known for different species and in different states of the chemical reaction; however, structural dynamics of the substrate binding to the catalytic site of GGT is unknown. Here, we modeled Escherichia Coli GGTs glutamine binding by using a swarm of accelerated molecular dynamics (aMD) simulations. Characterization of multiple binding events identified three structural binding motifs composed of polar residues in the binding pocket that govern glutamine binding into the active site. Simulated open and closed conformations of a lid-loop protecting the binding cavity suggests its role as a gating element by allowing or blocking substrates entry into the binding pocket. Partially open states of the lid-loop are accessible within thermal fluctuations, while the estimated free energy cost of a complete open state is 2.4 kcal/mol. Our results suggest that both specific electrostatic interactions and GGT conformational dynamics dictate the molecular recognition of substrate-GGT complexes.

biophysics↗