Biology subjects

Midtgaard, S. R.

Publications and source records attributed to Midtgaard, S. R..

3 recordsLinked to original sources

bioRxiv2020

Lipid-bound ApoE3 self-assemble into elliptical disc-shaped particles

Apolipoproteins are vital to lipid metabolism and cholesterol transport in the human body. Here we present a structural study of the lipid-bound particles formed by ApoE3 in a full-length and a truncated version. The particles are formed with, respectively, POPC and DMPC and investigated by small-angle X-ray scattering and negative stain electron microscopy. We find that lipid-bound ApoE3 particles are elliptical, disc-shaped particles composed of a central lipid bilayer encircled by two amphipathic ApoE3 proteins. We went on to investigate a truncated form of ApoE3 containing only residue 80 to 255 (ApoE380-255), which is the central helical repeat segment of ApoE3. The lipid-bound ApoE380-255 particles are found to have the same morphology as the particles with full-length ApoE3. However, they are larger, and form more heterogeneous discoidal structures with four proteins per particle. This behavior is in contrast to ApoA1 where the highly similar helical repeat domain determines the size and stoichiometry of the formed particles both in the case of full-length and truncated ApoA1. Our data hence points towards different mechanisms for lipid bilayer structural modulation by ApoA1 and ApoE3 due to different roles of the non-repeat segments.

biochemistry↗

bioRxiv2019

Structure and dynamics of a lipid nanodisc by integrating NMR, SAXS and SANS experiments with molecular dynamics simulations

Nanodiscs are membrane mimetics that consist of a protein belt surrounding a lipid bilayer, and are broadly used for characterization of membrane proteins. Here, we investigate the structure, dynamics and biophysical properties of two small nanodiscs, MSP1D1{Delta}H5 and {Delta}H4H5. We combine our SAXS and SANS experiments with molecular dynamics simulations and previously obtained NMR and EPR data to derive and validate a conformational ensemble that represents the structure and dynamics of the nanodisc. We find that it displays conformational heterogeneity with various elliptical shapes, and with substantial differences in lipid ordering in the centre and rim of the discs. Together, our results reconcile previous apparently con2icting observations about the shape of nanodiscs, and paves the way for future integrative studies of larger complex systems such as membrane proteins embedded in nanodiscs.

biophysics↗

bioRxiv2018

Structure and dynamics of the central lipid pool and protein components of the bacterial holo-translocon

The bacterial Sec translocon, SecYEG, associates with accessory proteins YidC and the SecDF-YajC subcomplex to form the bacterial holo-translocon (HTL). The HTL is a dynamic and flexible protein transport machine capable of coordinating protein secretion across the membrane, and efficient lateral insertion of nascent membrane proteins. It has been hypothesized that a central lipid core facilitates the controlled passage of membrane proteins into the bilayer, ensuring efficient formation of their native state. By performing small-angle neutron scattering (SANS) on protein solubilized in match-out deuterated detergent, we have been able to interrogate a naked HTL complex, with the scattering contribution of the surrounding detergent micelle rendered invisible. Such an approach has allowed the confirmation of a lipid core within the HTL, which accommodates between 8 and 29 lipids. Coarse-grained molecular dynamics simulations of the HTL also demonstrate a dynamic, central pool of lipids. An opening at this lipid rich region between YidC and the SecY lateral gate may provide an exit gateway for newly synthesized, correctly oriented, membrane protein helices to emerge from the HTL.

biophysics↗