Design of PG-Surfactants Bearing Polyacrylamide Polymer Chain to Solubilize Membrane Proteins in a Surfactant-Free Buffer

The development of techniques capable of using membrane proteins in a surfactant-free aqueous buffer is an attractive research area, and it should be elucidated for various membrane protein studies. To this end, we examined a method using new solubilization surfactants that do not detach from membrane protein surfaces once bound. The designed solubilization surfactants, DKDKC(12)K-PA(n) (n = 5, 7, and 18), consist of two parts: one is the lipopeptide-based solubilization surfactant part, DKDKC(12)K, fand the other is the covalently connected linear polyacrylamide (PA) chain with different M(w) values of 5, 7, or 18 kDa. Intermolecular interactions between the PA chains in DKDKC(12)K-PA(n) concentrated on the surfaces of membrane proteins via amphiphilic binding of the DKDKC(12)K part to the integral membrane domain was observed. Therefore, DKDKC(12)K-PA(n) (n = 5, 7, and 18) could maintain a bound state even after removal of the unbound by ultrafiltration or gel-filtration chromatography. We used photosystem I (PSI) from Thermosynecoccus vulcanus as a representative to assess the impacts of new surfactants on the solubilized membrane protein structure and functions. Based on the maintenance of unique photophysical properties of PSI, we evaluated the ability of DKDKC(12)K-PA(n) (n = 5, 7, and 18) as a new solubilization surfactant.