Biology subjects

Vattulainen, I.

Publications and source records attributed to Vattulainen, I..

22 records · Page 2Linked to original sources

bioRxiv2020

Determinants for forming a supramolecular myelin-like proteolipid lattice

Myelin protein P2 is a peripheral membrane protein of the fatty acid binding protein family. It functions in the formation and maintenance of the peripheral nerve myelin sheath, and several P2 mutations causing human Charot-Marie-Tooth neuropathy have been reported. Here, electron cryomicroscopy of myelin-like proteolipid multilayers revealed a three-dimensionally ordered lattice of P2 molecules between stacked lipid bilayers, visualizing its possible assembly at the myelin major dense line. A single layer of P2 is inserted between two bilayers in a tight intermembrane space of [~]3 nm, implying direct interactions between P2 and two membrane surfaces. Further details on lateral protein organization were revealed through X-ray diffraction from bicelles stacked by P2. Surface mutagenesis of P2 coupled to structural and functional experiments revealed a role for both the portal region and the opposite face of P2 in membrane interactions. Atomistic molecular dynamics simulations of P2 on myelin-like and model membrane surfaces suggested that Arg88 is an important residue for P2-membrane interactions, in addition to the helical lid domain on the opposite face of the molecule. Negatively charged myelin lipid headgroups anchor P2 stably on the bilayer surface. Membrane binding may be accompanied by opening of the P2 {beta} barrel structure and ligand exchange with the apposing lipid bilayer. Our results provide an unprecedented view into an ordered, multilayered biomolecular membrane system induced by the presence of a peripheral membrane protein from human myelin. This is an important step towards deciphering the 3-dimensional assembly of a mature myelin sheath at the molecular level.

biochemistry↗

bioRxiv2019

The α1 subunit of the Na,K-ATPase acts upstream of PI(4,5)P2 facilitating unconventional secretion of Fibroblast Growth Factor 2 from tumor cells

Fibroblast Growth Factor 2 (FGF2) is a tumor cell survival factor that is exported from cells by an unconventional secretory pathway. This process is based on direct translocation of FGF2 across the plasma membrane. FGF2 membrane translocation depends on PI(4,5)P2-induced formation of membrane-inserted FGF2 oligomers followed by extracellular trapping of FGF2 at the outer leaflet mediated by cell surface heparan sulfate proteoglycans. Beyond the well-characterized core mechanism of FGF2 membrane translocation, the Na,K-ATPase has been proposed to play a so far unknown role in unconventional secretion of FGF2. Here, we define a direct physical interaction of FGF2 with a subdomain of the cytoplasmic part of the 1 subunit of the Na,K-ATPase. Employing NMR spectroscopy and molecular dynamics simulations, we identified two lysine residues on the molecular surface of FGF2 that are shown to be essential for its interaction with 1. In intact cells, the corresponding lysine-to-glutamate variants of FGF2 were characterized by inefficient secretion and reduced recruitment to the inner plasma membrane leaflet as shown by single molecule TIRF microscopy. Our findings suggest that 1 acts upstream of PI(4,5)P2 facilitating efficient membrane translocation of FGF2 to the cell surface of tumor cells.

biochemistry↗

bioRxiv2019

Antidepressants act by binding to the cholesterol-interaction site at TRKB neurotrophin receptor

It is unclear how binding of antidepressant drugs to their targets gives rise to the clinical antidepressant effect. We discovered that the transmembrane domain of TRKB, the brain-derived neurotrophic factor (BDNF) receptor that promotes neuronal plasticity and antidepressant responses, has a cholesterol-sensing function that mediates synaptic effects of cholesterol. We then found that both typical and fast-acting antidepressants directly bind to TRKB, thereby facilitating synaptic localization of TRKB and its activation by BDNF. Extensive computational approaches including atomistic molecular dynamics simulations revealed a binding site at the transmembrane region of TRKB dimers. Mutation of the TRKB antidepressant-binding motif impaired cellular, behavioral and plasticity-promoting responses to antidepressants in vitro and in vivo. We suggest that binding to TRKB and the allosteric facilitation of BDNF signaling is the common mechanism for antidepressant action, which proposes a framework for how molecular effects of antidepressants are translated into clinical mood recovery.

neuroscience↗

bioRxiv2019

Cryo-EM structure of the complete and ligand-saturated insulin receptor ectodomain

Glucose homeostasis and growth essentially depend on the peptide hormone insulin engaging its receptor. Despite biochemical and structural advances, a fundamental contradiction has persisted in the current understanding of insulin ligand-receptor interactions. While biochemistry predicts two distinct insulin binding sites, 1 and 2, recent structural analyses have only resolved site 1. Using a combined approach of cryo-EM and atomistic molecular dynamics simulation, we determined the structure of the entire dimeric insulin receptor ectodomain saturated with four insulin molecules. Complementing the previously described insulin-site 1 interaction, we present the first view of insulin bound to the discrete insulin receptor site 2. Insulin binding stabilizes the receptor ectodomain in a T-shaped conformation wherein the membrane-proximal domains converge and contact each other. These findings expand the current models of insulin binding to its receptor and of its regulation. In summary, we provide the structural basis enabling a comprehensive description of ligand-receptor interactions that ultimately will inform new approaches to structure-based drug design.\n\nIn briefA cryo-EM structure of the complete insulin receptor ectodomain saturated with four insulin ligands is reported. The structural model of the insulin-insulin receptor complex adopts a T-shaped conformation, reveals two additional insulin-binding sites potentially involved in the initial interaction of insulin with its receptor, and resolves the membrane proximal region.

biochemistry↗