4.8 Article

Differences in SMA-like polymer architecture dictate the conformational changes exhibited by the membrane protein rhodopsin encapsulated in lipid nano-particles

Journal

NANOSCALE
Volume 13, Issue 31, Pages 13519-13528

Publisher

ROYAL SOC CHEMISTRY
DOI: 10.1039/d1nr02419a

Keywords

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Funding

  1. Biotechnology and Biological Sciences Research Council (BBSRC) [BB/R016615/1, BB/R016755/1, BB/S008160/1]
  2. BBSRC-MIBTP award
  3. Medical Research Council (MRC) [U105197215]
  4. South African Research Chairs Initiative of the Department of Science and Technology (DST)
  5. National Research Foundation (NRF) of South Africa [46855]
  6. BBSRC [BB/R016755/1, BB/S008160/1, BB/R016615/1] Funding Source: UKRI

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Membrane proteins encapsulated in various polymer-based nano-encapsulation strategies exhibit different conformational changes, leading to the generation of diverse intermediate states for the proteins, which can be useful for studying membrane proteins effectively.
Membrane proteins are of fundamental importance to cellular processes and nano-encapsulation strategies that preserve their native lipid bilayer environment are particularly attractive for studying and exploiting these proteins. Poly(styrene-co-maleic acid) (SMA) and related polymers poly(styrene-co-(N-(3-N ',N '-dimethylaminopropyl)maleimide)) (SMI) and poly(diisobutylene-alt-maleic acid) (DIBMA) have revolutionised the study of membrane proteins by spontaneously solubilising membrane proteins direct from cell membranes within nanoscale discs of native bilayer called SMA lipid particles (SMALPs), SMILPs and DIBMALPs respectively. This systematic study shows for the first time, that conformational changes of the encapsulated protein are dictated by the solubilising polymer. The photoactivation pathway of rhodopsin (Rho), a G-protein-coupled receptor (GPCR), comprises structurally-defined intermediates with characteristic absorbance spectra that revealed conformational restrictions with styrene-containing SMA and SMI, so that photoactivation proceeded only as far as metarhodopsin-I, absorbing at 478 nm, in a SMALP or SMILP. In contrast, full attainment of metarhodopsin-II, absorbing at 382 nm, was observed in a DIBMALP. Consequently, different intermediate states of Rho could be generated readily by simply employing different SMA-like polymers. Dynamic light-scattering and analytical ultracentrifugation revealed differences in size and thermostability between SMALP, SMILP and DIBMALP. Moreover, encapsulated Rho exhibited different stability in a SMALP, SMILP or DIBMALP. Overall, we establish that SMA, SMI and DIBMA constitute a 'toolkit' of solubilising polymers, so that selection of the appropriate solubilising polymer provides a spectrum of useful attributes for studying membrane proteins.

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