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Creative Biolabs provides excellent detergent-free membrane protein purification service with the use of novel polymers approaches.
Purification of membrane protein is the essential process for the structure determination of protein, which is usually achieved via the conventional water-soluble (detergent-lipid-protein) complex method. However, detergent, a kind of surfactants, can induce the dissociation of the subunits, as a result, inactivating the membrane protein. To overcome this, an alternative polymer technique is designed to keep membrane protein soluble in water without detergent, which is used after the solubilization process.
Nowadays, there are two amphipathic polymers can be employed to perform the detergent-free membrane protein purification.
Amphipols (e.g. A8-35) are synthesized via the formation of amide bonds between octylamine and the carboxylic groups of low-molecular-weight polyacrylic acid precursors. The end-products are co- or terpolymers, in which the grafted side chains or groups are randomly distributed along the main chain. The amphipols have the ability to make the transmembrane regions of proteins “trapped” around by these polymers, so as to keep hydrophobic domains stay folded. Amphipols have been used to successfully solubilize a number of proteins, such as GPCRs, with no biological function change (Figure 1).
Figure 1. An example of amphipol A8-35 purifying procedure. (PNAS, 2005)
Poly (styrene-co-maleic acid) lipid particles (SMALPs), also a kind of low-molecular-weight chemical, are able to reversibly encapsulate membrane protein. The polymer itself is made of alternating hydrophilic (maleic acid) and hydrophobic (styrene) moieties. SMALPs are ideally suited to purification and further biochemical studies (such as drug discovery) due to its characterisctics of high temperature resistance and pH sensitivity. The SMALPs are synthetised by the simple addition of SMA co-polymer to the membrane circumstance containing the protein of interest. At neutral or alkaline pH, a disc-like structure assembles itself, encapsulating the membrane protein in a form amenable to be purified. At acidic pH, the polymer disassociates from the particle to leave the membrane protein containing complex alone (Figure 2).
Figure 2. Diagrammatic representation of lipid and membrane protein encapsulation by SMALPs
M. Jamshad, et al. (2011). Surfactant-free purification of membrane proteins with intact native membrane environment. Biochem Soc Trans 39: 813-818.
C. Tribet, et al. (1996). Amphipols: Polymers that keep membrane proteins soluble in. Proc Natl Acad Sci U S A 93: 15047-15050.
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