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Dimerization of Terminal Domains in Spiders Silk Proteins Is Controlled by Electrostatic Anisotropy and Modulated by Hydrophobic Patches

Kurut, Anil LU ; Dicko, Cedric LU and Lund, Mikael LU (2015) In ACS Biomaterial Science and Engineering 1(6). p.363-371
Abstract

The well-tuned spinning technology from spiders has attracted many researchers with the promise of producing high-performance, biocompatible, and yet biodegradable fibers. So far, the intricate chemistry and rheology of spinning have eluded us. A breakthrough was achieved recently, when the 3D structures of the N and C terminal domains of spider dragline silk were resolved and their pH-induced dimerization was revealed. To understand the terminal domains' dimerization mechanisms, we developed a protein model based on the experimental structures that reproduces charge and hydrophobic anisotropy of the complex protein surfaces. Monte Carlo simulations were used to study the thermodynamic dimerization of the N-terminal domain as a function... (More)

The well-tuned spinning technology from spiders has attracted many researchers with the promise of producing high-performance, biocompatible, and yet biodegradable fibers. So far, the intricate chemistry and rheology of spinning have eluded us. A breakthrough was achieved recently, when the 3D structures of the N and C terminal domains of spider dragline silk were resolved and their pH-induced dimerization was revealed. To understand the terminal domains' dimerization mechanisms, we developed a protein model based on the experimental structures that reproduces charge and hydrophobic anisotropy of the complex protein surfaces. Monte Carlo simulations were used to study the thermodynamic dimerization of the N-terminal domain as a function of pH and ionic strength. We show that the hydrophobic and electrostatic anisotropies of the N-terminal domain cooperate constructively in the association process. The dipolar attractions at pH 6 lead to weakly bound dimers by forcing an antiparallel monomer orientation, stabilized by hydrophobic locking at close separations. Elevated salt concentrations reduce the thermodynamic dimerization constant due to screened electrostatic dipolar attraction. Moreover, the mutations on ionizable residues reveal a free energy of binding, proportional to the dipole moment of the mutants. It has previously been shown that dimers, formed at pH 6, completely dissociate at pH 7, which is thought to be due to altered protein charges. In contrast, our study indicates that the pH increase has no influence on the charge distribution of the N-terminal domain. Instead, the pH-induced dissociation is due to an adapted, loose conformation at pH 7, which significantly hampers both electrostatic and hydrophobic attractive interactions.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
dimer formation, electrostatic anisotropy, hydrophobic patchiness, Monte Carlo simulation, silk assembly, silk termini domains
in
ACS Biomaterial Science and Engineering
volume
1
issue
6
pages
9 pages
external identifiers
  • Scopus:84969188108
DOI
10.1021/ab500039q
language
English
LU publication?
yes
id
12013b7e-3d9f-4285-8de6-0d342488f969
date added to LUP
2016-10-13 16:02:36
date last changed
2016-10-13 16:02:36
@misc{12013b7e-3d9f-4285-8de6-0d342488f969,
  abstract     = {<p>The well-tuned spinning technology from spiders has attracted many researchers with the promise of producing high-performance, biocompatible, and yet biodegradable fibers. So far, the intricate chemistry and rheology of spinning have eluded us. A breakthrough was achieved recently, when the 3D structures of the N and C terminal domains of spider dragline silk were resolved and their pH-induced dimerization was revealed. To understand the terminal domains' dimerization mechanisms, we developed a protein model based on the experimental structures that reproduces charge and hydrophobic anisotropy of the complex protein surfaces. Monte Carlo simulations were used to study the thermodynamic dimerization of the N-terminal domain as a function of pH and ionic strength. We show that the hydrophobic and electrostatic anisotropies of the N-terminal domain cooperate constructively in the association process. The dipolar attractions at pH 6 lead to weakly bound dimers by forcing an antiparallel monomer orientation, stabilized by hydrophobic locking at close separations. Elevated salt concentrations reduce the thermodynamic dimerization constant due to screened electrostatic dipolar attraction. Moreover, the mutations on ionizable residues reveal a free energy of binding, proportional to the dipole moment of the mutants. It has previously been shown that dimers, formed at pH 6, completely dissociate at pH 7, which is thought to be due to altered protein charges. In contrast, our study indicates that the pH increase has no influence on the charge distribution of the N-terminal domain. Instead, the pH-induced dissociation is due to an adapted, loose conformation at pH 7, which significantly hampers both electrostatic and hydrophobic attractive interactions.</p>},
  author       = {Kurut, Anil and Dicko, Cedric and Lund, Mikael},
  keyword      = {dimer formation,electrostatic anisotropy,hydrophobic patchiness,Monte Carlo simulation,silk assembly,silk termini domains},
  language     = {eng},
  month        = {06},
  number       = {6},
  pages        = {363--371},
  series       = {ACS Biomaterial Science and Engineering},
  title        = {Dimerization of Terminal Domains in Spiders Silk Proteins Is Controlled by Electrostatic Anisotropy and Modulated by Hydrophobic Patches},
  url          = {http://dx.doi.org/10.1021/ab500039q},
  volume       = {1},
  year         = {2015},
}