Although there is a growing interest in using polymer lipid-nanodiscs, the polymer charge poses limitations for studies on membrane proteins. Here, we demonstrate the functional reconstitution of a large soluble-domain containing positively-charged ∼57 kDa cytochrome-P450 and negatively-charged ∼16 kDa cytochrome-b5 in lipid-nanodiscs, and the role of the polymer charge for high-resolution studies on membrane proteins.

spectroscopy has been applied to study the urea effect on phase transition of two similar thermosensitive polymer hydrogels: poly(N-isopropylacrylamide) (PNIPAM) and poly(N,N-diethylacrylamide) (PDEA). It is found that urea influences the phase transition of the hydrogels in opposite ways: lowering the lower critical solution temperature (LCST) of PNIPAM and hence stabilizing its globular structure, whereas raising the LCST of PDEA and destabilizing the globular structure. The selfdiffusion coefficient and urea−polymer nuclear Overhauser effect (NOE) measurement reveal that urea has a stronger interaction with PNIPAM than with PDEA. Moreover, the enhanced positive water−PNIPAM NOE suggests that urea not only interacts directly with PNIPAM via hydrogen bond but also intensifies the hydrogen bonding interaction between water and PNIPAM. We suggest that different urea−polymer hydrogen bonding interaction due to the presence or absence of amide hydrogen is correlated with the distinct LCST variation of PNIPAM and PDEA.