Biology subjects

Polyansky, A. A.

Publications and source records attributed to Polyansky, A. A..

4 recordsLinked to original sources

bioRxiv2022

On a mechanistic impact of transmembrane tetramerization in pathological activation of RTKs

Constitutive activation of receptor tyrosine kinases (RTKs) via different mutation has a strong impact into development of severe human disorders, including cancer. While pathological effect of such mutations can be common on the phenotypical level, mechanistic understanding of their contribution into the receptor activation depends on the exact molecular context. Mutations in transmembrane (TM) domains represent an interesting class of pathological modifications since they can directly affect a signal transduction pathway from the receptor to the kinase domains of RTKs. Here we propose a putative activation scenario of RTK, whereby TM mutations can also promote higher order oligomerization of the receptors that leads to the subsequent ligand-free activation. To illustrate this model with all-atom resolution for a previously characterized oncogenic TM mutation V536E in platelet-derived growth factor receptor alpha (PDGFRA), we use a computational modeling framework including sequence-based structure prediction and all-atom 1 {micro}s molecular dynamics (MD) simulations in a model membrane for the predicted configuration of the PDGFRA TM tetramers. We show that in the course of MD simulations the mutant tetramer retains stable and compact configuration, which is strengthened by tight protein-protein interactions. In contrast, the wild type tetramer demonstrates looser packing and tendency to dissociate. Such a structural organization shapes the dynamics of TM helices in the oligomeric state. Specifically, the mutation affects the characteristic motions of mutated TM helical segments by introducing additional non-covalent crosslinks in the middle of the TM tetramer, which work as mechanical hinges. This leads to dynamic decoupling of the C-termini from the rigidified N-terminal parts and facilitates higher possible displacement between the C-termini of the mutant TM helical regions. This, in turn, can provide more freedom to downstream kinase domains in their mutual rearrangement. The observed structural and dynamic effects of the V536E mutations in the context of PDGFRA TM tetramer provide an interesting possibility that an effect of oncogenic TM mutations can go beyond alternating structure and dynamics of TM dimeric states and also promote formation of higher-order oligomers that may directly contribute into the ligand independent signaling of PDGFRA and other RTKs.

biophysics↗

bioRxiv2022

A uniquely stable trimeric model of SARS-CoV-2 spike transmembrane domain

The spike (S) protein of SARS-CoV-2 effectuates membrane fusion and virus entry into target cells. Its transmembrane domain (TMD) represents a homotrimer of -helices anchoring the spike in the viral envelope. Although S-protein models available to date include the TMD, its precise configuration was given brief consideration. Understanding viral fusion entails realistic TMD models, while no reliable approaches towards predicting the 3D structure of transmembrane (TM) trimers exist. Here, we propose a comprehensive computational framework to model the spike TMD (S-TMD) based solely on its primary structure. First, we performed amino acid sequence pattern matching and compared molecular hydrophobicity potential (MHP) distribution on the helix surface against TM homotrimers with known 3D structures and thus selected the TMD of the tumour necrosis factor receptor 1 (TNFR-1) for subsequent template-based modelling. We then iteratively built an all-atom homotrimer model of S-TMD based on "dynamic MHP portraits" and residue variability motifs. In this model each helix possessed two overlapping interfaces interacting with either of the remaining helices, which include conservative residues I1216, F1220, I1227, M1229, and M1233. Finally, the stability of this and several alternative models (including a recent NMR structure) and a set of mutant forms was tested in all-atom molecular dynamics (MD) simulations in a POPC bilayer mimicking the viral envelope membrane. Unlike other configurations, our model trimer remained extraordinarily tightly packed over a microsecond-range MD and retained its stability when palmitoylated in accordance with experimental data. Palmitoylation had no significant impact on the TMD conformation nor the way in which the lipid bilayer was perturbed in the presence of the trimer. Overall, the resulting model of S-TMD conforms to known basic principles of TM helix packing and will be further used to explore the complex machinery of membrane fusion from a broader perspective beyond the TMD.

bioinformatics↗

bioRxiv2022

Protein compactness and interaction valency define the architecture of a biomolecular condensate across scales

Non-membrane-bound biomolecular condensates have been proposed to represent an important mode of subcellular organization in diverse biological settings. However, the fundamental principles governing the spatial organization and dynamics of condensates at the atomistic level remain unclear. The S. cerevisiae Lge1 protein is required for histone H2B ubiquitination and its N-terminal intrinsically disordered fragment (Lge11-80) undergoes robust phase separation. This study connects single- and multi-chain all-atom molecular dynamics simulations of Lge11-80 with the in vitro behavior of Lge11-80 condensates. Analysis of modelled protein-protein interactions elucidates the key determinants of Lge11-80 condensate formation and links configurational entropy, valency and compactness of proteins inside the condensates. A newly derived analytical formalism, related to colloid fractal cluster formation, describes condensate architecture across length scales as a function of protein valency and compactness. In particular, the formalism provides an atomistically resolved model of Lge11-80 condensates on the scale of hundreds of nanometers starting from individual protein conformers captured in simulations. The simulation-derived fractal dimensions of condensates of Lge11-80 and its mutants agree with their in vitro morphologies. The presented framework enables a multiscale description of biomolecular condensates and embeds their study in a wider context of colloid self-organization.

biophysics↗

bioRxiv2021

FIBCD1 is a Conserved Receptor for Chondroitin Sulphate Proteoglycans of the Brain Extracellular Matrix and a Candidate Gene for a Complex Neurodevelopmental Disorder

The brain extracellular matrix (ECM) is enriched in chondroitin sulphate proteoglycans (CSPGs) with variable sulphate modifications that intimately participate in brain maturation and function. Very little is known about how the changing biophysical properties of the CSPGs are signalled to neurons. Here, we report Fibrinogen C Domain Containing 1 (FIBCD1), a known chitin-binding receptor of the innate immune system, to be highly expressed in the hippocampus and to specifically bind CSPGs containing 4-O sulphate modification (CS-4S). Cultured Fibcd1 knockout (KO) neurons lack phenotypic and transcriptomic responses to CSPG stimulation. Further, Fibcd1 KO mice exhibit accumulation of CS-4S, likely resulting in deficits of hippocampal-dependent learning tasks and abrogated synaptic remodelling, a phenotype rescued by enzymatic digestion of CSPGs. Likewise, neuronal specific knockdown of a Fibcd1 orthologue in flies results in neuronal morphological changes at the neuromuscular junctions and behavioural defects. Finally, we report two undiagnosed patients with a complex neurodevelopmental disorder with deleterious variants in FIBCD1, strongly implicating FIBCD1 in the development of the disease. Taken together, our results demonstrate that FIBCD1 is a novel, evolutionarily conserved component of ECM sulphation recognition that is crucial for neuronal development and function.

neuroscience↗