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Mechanism of the Spontaneous and Directional Membrane Insertion of a 2‑Transmembrane Ion Channel
journal contribution
posted on 2016-12-13, 00:00 authored by Steffen Altrichter, Maximilian Haase, Belinda Loh, Andreas Kuhn, Sebastian LeptihnProtein
insertion into membranes is a process occurring in every
cell and every cellular compartment. Yet, many thermodynamic aspects
of this fundamental biophysical process are not well understood. We
investigated physicochemical parameters that influence protein insertion
using the model protein KcsA, a 2-transmembrane ion channel. To understand
what drives insertion and to identify individual steps of protein
integration into a highly apolar environment, we investigated the
contribution of electrostatic interactions and lipid composition on
protein insertion on a single molecule level. We show that insertion
of KcsA is spontaneous and directional as the cytosolic part of the
protein does not translocate across the membrane barrier. Surprisingly,
not hydrophobic residues but charged amino acids are crucial for the
insertion of the unfolded protein into the membrane. Our results demonstrate
the importance of electrostatic interactions between membrane and
protein during the insertion process of hydrophobic polypeptides into
the apolar membrane. On the basis of the observation that negatively
charged lipids increase insertion events while high ionic strength
in the surrounding aqueous phase decreases insertion events, a two-step
mechanism is proposed. Here, an initial electrostatic attraction between
membrane and protein represents the first step prior to insertion
of hydrophobic residues into the hydrocarbon core of the membrane.
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cytosolic partphase decreases insertion eventshydrocarbon corelipid compositioninsertion processphysicochemical parametersdrives insertionmembrane barrierlipids increase insertion eventsDirectional Membrane Insertionprotein insertioninfluence protein insertionmodel protein KcsA2- transmembrane ion channelapolar membraneapolar environmentprotein integrationmolecule level
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