Chromatic acclimation in phototrophic marine cryptophytes

在某些蓝藻中，显色驯化(CA)是一个很好地理解的过程，它在变化的光条件下优化光合作用捕光。捕光藻胆体(PBS)的组成随着环境光颜色的变化而改变。在先前定义的蓝藻CA类型中，那些在绿色和红色光照下分别改变其吸收绿光的藻红蛋白(PE)和吸收红光的藻蓝蛋白(PC)的比例的类型是众所周知的。海洋蓝藻中的CA4，其中吸收光的藻胆素发色团在PBP内交换，也得到了很好的研究。最近，在某些隐芽藻类中也观察到了类似的现象。隐芽藻是一种双鞭毛类真核微藻，存在于各种水生生境中。许多物种使用独特的藻胆蛋白进行氧合光合作用，与蓝藻不同的是，藻胆蛋白不是在PBS中组织的，而是在类囊体腔中溶解的。由于PC569的存在，海洋物种隐色半边藻在569 nm处有一个主吸收峰。在红光下生长时，这一主吸收峰向625 nm方向移动，而在绿光下生长时，569 nm处的吸收峰占主导地位。在这项建议中，我们旨在阐明隐色隐色藻中这种CA现象的潜在机制。PC569将从不同光质下生长的细胞中分离出来，并结合UV-Vis光谱、高效液相色谱分析和质谱分析来分析藻胆蛋白和蛋白质组成。已鉴定的藻胆蛋白将与隐色隐色杆菌基因组中编码的五种铁氧还蛋白依赖的胆碱还原酶合成的藻胆蛋白进行比较。这些酶将线性四吡咯胆绿素转化为各种捕光藻胆蛋白发色团。由于PC569可能具有隐芽植物特有的一种丙烯酰胆素，我们将采取初步步骤来阐明这些胆素的生物合成途径。为此，将通过对生物合成蛋白质的特异性抑制来鉴定含有丙烯酰基的中间体。随后，将建立一种酶试验，为使用传统方法进行酶分离创造先决条件。总体而言，该项目将有助于更好地了解海洋隐芽植物适应不断变化的光照质量的情况。

Chromatic acclimation (CA) is a fairly well understood process in certain cyanobacteria that optimizes photosynthetic light-harvesting under changing light conditions. The composition of light-harvesting phycobilisomes (PBS) is remodeled as the ambient light color changes. Of the previously defined CA types in cyanobacteria, those that change their ratio of green light-absorbing phycoerythrin (PE) to red light-absorbing phycocyanin (PC) under green and red illumination, respectively, are well known. CA4 in marine cyanobacteria, in which the light-absorbing phycobilin chromophores are exchanged within the PBP, is also quite well studied. More recently, a similar phenomenon has also been observed in certain cryptophyte algae. Cryptophytes are biflagellate eukaryotic microalgae found in a variety of aquatic habitats. Many species perform oxygenic photosynthesis using unique phycobiliproteins that, unlike those of cyanobacteria, are not organized in PBS but are soluble in the thylakoid lumen. The marine species Hemiselmis cryptochromatica has a major absorption peak at 569 nm due to the presence of the PC569. When growing under red light, this main absorption peak shifts towards 625 nm, while for cells growing under green light, the peak at 569 nm dominates. In this proposal, we aim to elucidate the underlying mechanism of this CA phenomenon in H. cryptochromatica. PC569 will be isolated from cells grown under different light qualities and analyzed for phycobilin and protein composition using a combination of UV-vis spectrometry, HPLC analysis, and mass spectrometry. The identified phycobilins will be compared to those synthesized by the five ferredoxin-dependent bilin reductases encoded in the H. cryptochromatica genome. These enzymes convert the linear tetrapyrrole biliverdin into various light-harvesting phycobilin chromophores. Since PC569 likely possesses one of the cryptophyte-specific acryoyl bilins, bilin 584, we will take initial steps to elucidate the biosynthetic pathway to these bilins. For this purpose, acryoyl-containing intermediates will be identified by specific inhibition of biosynthetic proteins. Subsequently, an enzyme assay will be established to create the prerequisites for enzyme isolation using traditional methods. Overall, this project will contribute to a better understanding of the adaptation of marine cryptophytes to changing light qualities.