Rätsep Margus, Kangur Liina, Leiger Kristjan, Wang-Otomo Zheng-Yu, Freiberg Arvi
Institute of Physics, University of Tartu, W. Ostwaldi 1, 50411 Tartu, Estonia.
Faculty of Science, Ibaraki University, Mito 310-8512, Japan.
Biochim Biophys Acta Bioenerg. 2025 Jan 1;1866(1):149527. doi: 10.1016/j.bbabio.2024.149527. Epub 2024 Nov 16.
The resilience of biological systems to fluctuating environmental conditions is a crucial evolutionary advantage. In this study, we examine the thermo- and piezo-stability of the LH1-RC pigment-protein complex, the simplest photosynthetic unit, in three species of phototropic purple bacteria, each containing only this core complex. Among these species, Blastochloris viridis and Blastochloris tepida utilize bacteriochlorophyll b as the main light-harvesting pigment, while Rhodospirillum rubrum relies on bacteriochlorophyll a. Through spectroscopic analyses, we observed limited reversibility in the effects of temperature and pressure, likely due to the malleability of pigment binding sites within the light-harvesting LH1 complex. In terms of thermal robustness, LH1 complexes in a detergent environment progressively dissociate into dimeric (B820) and monomeric (B777) subunits. However, in the native membrane, degradation primarily occurs directly into B777 without the intermediate formation of B820. Interestingly, while high-pressure compression of core complexes from Blastochloris viridis and Blastochloris tepida caused significant changes in compressibility around 1.3 kbar and the formation of B777 and B820 subunits upon decompression, no such compressibility changes or pressure-induced dissociation were observed in Rhodospirillum rubrum complexes, even at pressures as high as 11 kbar. This study reveals significant differences in the piezo- and thermal properties of phototrophs containing either BChl a or BChl b, underscoring the critical role of structural factors in understanding the temperature- and pressure-induced denaturation phenomena in photosynthetic complexes. Rhodospirillum rubrum, in particular, stands out as one of the most thermodynamically stable systems among phototrophic microorganisms, capable of withstanding temperatures up to 70 °C and pressures exceeding 11 kbar.
生物系统对波动环境条件的适应能力是一项至关重要的进化优势。在本研究中，我们研究了三种趋光性紫色细菌中最简单的光合单元LH1-RC色素蛋白复合体的热稳定性和压稳定性，这三种细菌均仅含有该核心复合体。在这些物种中，绿囊色杆菌和温热囊色杆菌利用细菌叶绿素b作为主要的捕光色素，而深红红螺菌则依赖细菌叶绿素a。通过光谱分析，我们观察到温度和压力的影响具有有限的可逆性，这可能是由于捕光LH1复合体内色素结合位点的可塑性所致。在热稳定性方面，处于去污剂环境中的LH1复合体逐渐解离为二聚体（B820）和单体（B777）亚基。然而，在天然膜中，降解主要直接发生为B777，而不会形成中间产物B820。有趣的是，虽然对绿囊色杆菌和温热囊色杆菌的核心复合体进行高压压缩会在约1.3千巴时导致压缩性发生显著变化，并在减压时形成B777和B820亚基，但即使在高达11千巴的压力下，深红红螺菌复合体中也未观察到这种压缩性变化或压力诱导的解离现象。这项研究揭示了含有细菌叶绿素a或细菌叶绿素b的光合生物在压稳定性和热稳定性方面存在显著差异，强调了结构因素在理解光合复合体中温度和压力诱导的变性现象方面的关键作用。特别是，深红红螺菌是光合微生物中热力学最稳定的系统之一，能够承受高达70°C的温度和超过11千巴的压力。
