Different Mechanisms of Chloride-associated Proton Flux in Various Halorhodopsins Unveiled by Photoelectrochemical Measurements
Date Issued
2016
Date
2016
Author(s)
Huang, Yuan-Chi
Abstract
Halorhodopsin (HR) is a seven-transmembrane (7TM) retinylidene protein from haloarchaea that is commonly known to function as a light-driven inward chloride pump. However, previous studies have indicated that despite the general characteristics that most HRs share, HRs from distinct species differ in many aspects. We present indium-tin oxide (ITO)-based photocurrent measurements that demonstrate light-induced signal generated by proton release, which is observed solely in NpHR through purified protein-based assays, indeed showed HRs are not all identical. Mutagenesis studies were conducted on several conserved residues considered critical for chloride stability in HRs. Intriguingly, the photocurrent signals were eliminated after specific point mutation. Furthermore, the photocurrent and various photocycle intermediates were recorded simultaneously. We summarized three possible mechanisms in attempt to explain the differences among HRs. Overall, this approach provides a high-resolution method for further investigation of the chloride-associated proton-translocation mechanism.
Subjects
haloarchaea
halorhodopsin
light-driven chloride pump
photocurrent
photocycle
Type
thesis
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