Amphiphilic block copolymers significantly influence functions of bacteriorhodopsin in water

Dewang Ma, Yazhuo Wang, Jia Wu, Yingchun Zhao, Ming Ming, and Jiandong Ding*, Soft Matter, (accepted in July, 2010)

In our previous Communication (Soft Matter 2009), a diacrylated Pluronic copolymer was applied as a macromonomer to prepare a chemically-crosslinked hydrogel encapsulating bacteriorhodopsin (BR), and we surprisingly found that the photochromic response of BR was prolonged over 30 min even under high water content conditions by combination of gene mutation and copolymer modification. So, replacing a detergent by a macromolecular amphiphile produced a significant effect on the lifetime of the M intermediate of BR.

While that Communication reports a novel phenomenon, this full paper investigates the origin of this phenomenon. Here we expand the study of the effect of copolymers on protein functions in four ways: (1) we used native BR instead of a gene-engineering D96N mutant; (2) effects on both photoelectric and photochromic responses of BR instead of merely photochromic response were examined; (3) EO₂₃-PO₆₅-EO₂₃ (P123) and other 6 Pluronic copolymers instead of a diacrylated F127 macromer were used as model polymers; (4) M decay behaviors of BR/P123 assemblies in a solution and a dried PVA film was compared. The effects of synthetic polymers on functions of BR described in the present paper thus show several universal features, and the underlying reasons are partially discussed.