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Insight into a single halobacterium using a dual‐bacteriorhodopsin system with different functionally optimized pH ranges to cope with periplasmic pH changes associated with continuous light illumination
Author(s) -
Fu HsuYuan,
Yi HsiuPing,
Lu YenHsu,
Yang ChiiShen
Publication year - 2013
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/mmi.12208
Subject(s) - halobacterium salinarum , bacteriorhodopsin , periplasmic space , proton transport , archaea , biology , biochemistry , photocurrent , halobacteriaceae , proton , biophysics , gene , escherichia coli , materials science , membrane , optoelectronics , physics , quantum mechanics
Summary The light‐driven outward proton transporter assists energy production via an ATP synthase system best exemplified by the bacteriorhodopsin ( BR ) from H alobacterium salinarum , Hs BR . As the only archaea able to survive in the resource‐limited ecosystem of the D ead S ea, H aloarcula marismortui has been reported to have a unique dual‐ BR system, consisting of Hm BRI and Hm BRII , instead of only a single BR in a cell (solo‐ BR ). The contribution of this dual‐ BR system to survival was investigated. First, native H . marismortui and H . salinarum cells were tested in water that had been adjusted to mimic the conditions of D ead S ea water. These archaea were shown to accumulate protons and reduce pH in their periplasmic regions, which disabled further proton transportation functionality in H . salinarum but not in H . marismortui . Then, pH ‐dependent photocurrent measurements using purified BR proteins demonstrated that Hs BR and Hm BRI were functional at pH > 5.0 and that Hm BRII was functional at pH > 4.0. Our results indicate that the dual‐ Hm BR system is composed of two BRs with different optimal functional pH ranges and together they maintain light‐driven proton transport activity under pH > 4.0, which might contribute the survival of H . marismortui under the acidic pH of the D ead S ea.