Specific refolding pathway of viscumin A chain in membrane-like medium reveals a possible mechanism of toxin entry into cell

Sci Rep. 2019 Jan 23;9(1):413. doi: 10.1038/s41598-018-36310-6.

Abstract

How is a water-soluble globular protein able to spontaneously cross a cellular membrane? It is commonly accepted that it undergoes significant structural rearrangements on the lipid-water interface, thus acquiring membrane binding and penetration ability. In this study molecular dynamics (MD) simulations have been used to explore large-scale conformational changes of the globular viscumin A chain in a complex environment - comprising urea and chloroform/methanol (CHCl3/MeOH) mixture. Being well-packed in aqueous solution, viscumin A undergoes global structural rearrangements in both organic media. In urea, the protein is "swelling" and gradually loses its long-distance contacts, thus resembling the "molten globule" state. In CHCl3/MeOH, viscumin A is in effect turned "inside out". This is accompanied with strengthening of the secondary structure and surface exposure of hydrophobic epitopes originally buried inside the globule. Resulting solvent-adapted models were further subjected to Monte Carlo simulations with an implicit hydrophobic slab membrane. In contrast to only a few point surface contacts in water and two short regions with weak protein-lipid interactions in urea, MD-derived structures in CHCl3/MeOH reveal multiple determinants of membrane interaction. Consequently it is now possible to propose a specific pathway for the structural adaptation of viscumin A with respect to the cell membrane - a probable first step of its translocation into cytoplasmic targets.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Membrane / chemistry*
  • Membranes, Artificial*
  • Protein Refolding*
  • Protein Transport
  • Ribosome Inactivating Proteins, Type 2 / chemistry*
  • Toxins, Biological / chemistry*

Substances

  • Membranes, Artificial
  • Ribosome Inactivating Proteins, Type 2
  • Toxins, Biological
  • mistletoe lectin I