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. Issue 3 (9th April 2013)

• Record Type: Journal Article
• Authors: Fu, Hsu‐Yuan; Yi, Hsiu‐Ping; Lu, Yen‐Hsu; Yang, Chii‐Shen
• Is Part Of: Molecular microbiology. Volume 88:Issue 3(2013)
• Page Start: 551
• Page End: 561
• Publication Date: 2013-04-09
• Subjects: Molecular microbiology -- Periodicals; 572.829
• DOI: 10.1111/mmi.12208
• Languages: English
• ISSNs: 0950-382X

Abstract

<abstract abstract-type="main"> <title>Summary</title> <p>The light‐driven outward proton transporter assists energy production via an ATP synthase system best exemplified by the bacteriorhodopsin (BR) from <italic>Halobacterium salinarum</italic>, <italic>Hs</italic>BR. As the only archaea able to survive in the resource‐limited ecosystem of the Dead Sea, <italic>Haloarcula marismortui</italic> has been reported to have a unique dual‐BR system, consisting of <italic>Hm</italic>BRI and <italic>Hm</italic>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 <italic>H. marismortui</italic> and <italic>H. salinarum</italic> cells were tested in water that had been adjusted to mimic the conditions of Dead Sea water. These archaea were shown to accumulate protons and reduce pH in their periplasmic regions, which disabled further proton transportation functionality in <italic>H. salinarum</italic> but not in <italic>H. marismortui</italic>. Then, pH‐dependent photocurrent measurements using purified BR proteins demonstrated that <italic>Hs</italic>BR and <italic>Hm</italic>BRI were functional at pH > 5.0 and that <italic>Hm</italic>BRII was functional at pH > 4.0. Our results indicate that the dual‐<italic>Hm</italic>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 <italic>H. marismortui</italic> under the acidic pH of the Dead Sea.</p> </abstract>