Nanotechnology Advance Enables High-Resolution Structural Studies of Membrane Proteins

However, a limiting factor in membrane protein research is the ability to solubilize and stabilize such proteins. Detergents are used most often for solubilizing membrane proteins, but they are associated with protein instability and poor compatibility with structural and biophysical studies.

Investigators at Karolinska Institutet (Stockholm, Sweden) recently described a saposin-lipoprotein nanoparticle system, which they called Salipro. This system allowed for the reconstitution of membrane proteins in a lipid environment that was stabilized by a scaffold of saposin proteins.

The investigators demonstrated the applicability of the method on two purified membrane protein complexes as well as by the direct solubilization and nanoparticle incorporation of a viral membrane protein complex from the virus membrane. This approach facilitated high-resolution structural studies of the bacterial peptide transporter PeptTSo2 by single-particle cryo-electron microscopy (cryo-EM) and enabled the stabilization of the HIV envelope glycoprotein in a functional state.

Cryo-EM is an analytical technique complementary to NRM and X-ray diffraction crystallography that provides near-atomic resolution without the requirements for crystallization or limits on molecular size and complexity imposed by the other techniques. Cryo-EM allows the observation of specimens that have not been stained or fixed in any way, showing them in their native environment while integrating multiple images to form a three-dimensional model of the sample.

"To our knowledge, the HIV spike protein preparation presented in the study using the Salipro system represents the first approach that allows the stabilization of the HIV-1 spike, including the important membrane domains, in a soluble and functional state", said senior author Dr. Pär Nordlund professor of oncology-pathology at Karolinska Institutet.

The paper describing the Salipro system was published in the March 7, 2016, online edition of the journal Nature Methods.

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