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Molecular Switch between Structural Compaction and Thermodynamic Stability by the Xxx–Pro Interface in Transmembrane β‑Barrels
journal contribution
posted on 2019-12-12, 13:11 authored by Bharat
Ramasubramanian Iyer, Swadha Gupta, Henna Noordeen, Roshika Ravi, Meera Daulatrao Pawar, Anjana George, Radhakrishnan MahalakshmiTransmembrane β-barrel scaffolds found in outer
membrane
proteins are formed and stabilized by a defined pattern of interstrand
intraprotein H-bonds, in hydrophobic lipid bilayers. Introducing the
conformationally constrained proline in β-barrels can cause
significant destabilization of these structural regions that require
H-bonding, with proline additionally acting as a secondary structure
breaker. Membrane protein β-barrels are therefore expected to
show poor tolerance to the presence of a transmembrane proline. Here,
we assign a thermodynamic measure for the extent to which a single
proline can be tolerated at the C-terminal interface of the model
transmembrane β-barrel PagP. We find that proline drastically
destabilizes PagP by 7.0 kcal mol–1 with respect
to wild-type PagP (F161 → P161). Interestingly,
strategic modulation of the preceding residue can modify the measured
energetics. Placing a hydrophobic or bulky side chain as the preceding
residue increases the thermodynamic stability by ≤8.0 kcal
mol–1. While polar substituents at the preceding
residue decrease the PagP stability, these residues demonstrate stronger
tertiary packing interactions in the barrel and retain the catalytic
activity of native PagP. This biophysical interplay between enhanced
thermodynamic stability and attaining a structurally compact functional
β-barrel scaffold highlights the detrimental effect caused by
proline incorporation. Our findings also reveal alternative mechanisms
that protein sequences can employ to salvage the structural integrity
of transmembrane protein structures.
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Keywords
proline incorporationside chainmembrane proteinsMolecular SwitchStructural CompactionPagP stabilitywild-type PagPresidue increaseslipid bilayersβ- barrel scaffoldC-terminal interfaceThermodynamic Stabilitystructure breakerinterstrand intraprotein H-bondsmodel transmembrane β- barrel PagPprotein sequencesalternative mechanismstransmembrane prolinetransmembrane protein structuresβ- barrelsMembrane protein β- barrelsresidue decrease
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