表現 Haloarcula marismortui 之六個光感受體揭露其獨特的感光特性

Expression of Six Photoreceptors in Haloarcula marismortui Unveiled Unique Photosensing Features

傅煦媛(Hsu-Yuan Fu)

指導教授 ： 楊啟伸

國立臺灣大學/生命科學院/微生物與生化學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.01804

摘要

在微生物中，光感受體 (photoreceptor) 對環境光照刺激反應，扮演十分重要的角色。目前為止，已經有超過 100 種的 photoreceptors 被鑑定出來。科學研究將它們分成四大類：包括 bacteriorhodopsin (BR)，其功能是將細胞內的氫離子運送到細胞外；halorhodopsin (HR) 則是將細胞外的氯離子運送到細胞內；sensory rhodopsin I (SRI) 同時具有調控正趨光及負趨光性；以及對於接近 UV 波長之光源有負趨光性之 sensory rhodopsin II (SRII)。
根據 2004 年完成的 Haloarcula marismortui 的基因體計畫，在其基因註解(annotation) 中，具有六個 photoreceptors，是目前所知在單一嗜鹽古細菌中最多的。本論文主要針對兩大問題：A) 訂出這六個預測的 photoreceptors 特徵吸收峰與其功能，以及 B) 這六個 photoreceptors 的生理角色。
本論文成功將六個 photoreceptors 選殖入 E. coli 表現系統且能順利表現，並得知：i) 這六個 photoreceptors 確實的特徵吸收峰；且 ii) 其特徵吸收峰在可見光譜上之分佈十分獨特；此外，iii) 鑑定出一個全新類型的 photoreceptor；並發現 iv) 這是第一個單一微生物體中，擁有兩個光驅動氫離子幫浦的光感受體，且其兩者之特徵吸收峰十分接近；最後，v) 照光影響基因 xop2 的蛋白質 (HmSRM) 表現量，初步證實 H. marismortui 可能具有光適應性生長的現象 (chromatic adaptation)。同時，本論文也在成功地確定這些 photoreceptors 的確具有標準 photoreceptors 特質後，有系統的為它們命名。

關鍵字

嗜鹽古細菌 ； Haloarcula marismortui ； 基因體計畫 ； 光感受體

並列摘要

Microbial photoreceptors play important roles when responding to environmental stimuli in microbes and a total of more than one hundred microbial photoreceptors has been identified. So far, four distinct functions have been identified, including bacteriorhodopsin (BR) that functions as outward proton pump, and halorhodopsin (HR) can serve as an inward chloride pump; sensory rhodopsin I (SRI) was shown to mediate both attract and repellent signaling, and sensory rhodopsin II (SRII) that triggers repellent signaling against near-UV light.
According to the genome project of the Haloarcula marismortui, there are six predicted photoreceptors, the most numbered photoreceptors in a single archaeon. This goals of this study will be: A) Determination of the maximum absorbance and functions of those six predicted photoreceptors and, B) the potential physiological roles of them.
We successful cloned and over-expressed all six photoreceptors using E. coli system, and concluded that: First, those six photoreceptors have their characteristic maximum absorbance, and second, a unique distribution pattern according to the maximum absorbance of those six photoreceptors. Third, a new type of sensory rhodopsin is identified; and fourth, two photoreceptors function as proton pumps and share the same maximum absorbance; the first time a single microbe found to have two light-driven proton pumps. Finally, chromatic adaptation is concluded in H. marismortui since different expression levels of HmSRM was observed when cells were grown under different wavelength of lights. Also, all of the photoreceptors were officially nominated after the confirmation of their characteristics as standard photoreceptors.

並列關鍵字

Haloarchaea ； Haloarcula marismortui ； genome project ； photoreceptor

參考文獻

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