Dedman Craig J, Chauhan Nishant, González-Lanchas Alba, Baldreki Chloë, Dowle Adam A, Larson Tony R, Lee Renee B Y, Rickaby Rosalind E M
Department of Earth Sciences, University of Oxford, South Parks Rd, Oxford, OX1 3AN, UK.
School of Geography, Earth and Environmental Sciences, Portland Square, University of Plymouth, Plymouth, PL4 8AA, UK.
Sci Rep. 2024 Dec 30;14(1):31821. doi: 10.1038/s41598-024-83052-9.
Coccolithophores comprise a major component of the oceanic carbon cycle. These unicellular algae produce ornate structures made of calcium carbonate, termed coccoliths, representing ~ 50% of calcite production in the open ocean. The exact molecular mechanisms which direct and control coccolith formation are unknown. In this study, we report on the presence and functional features of proteins within the coccoliths produced by a range of model coccolithophore species including: the globally abundant and well-studied Gephyrocapsa huxleyi (formerly Emiliania huxleyi) and related Gephyrocapsa oceanica, as well as the larger and more heavily calcified Coccolithus braarudii. Protein features were compared between species and against biomineralisation proteins previously identified in other marine calcifying organisms. Notably, several protein features were consistently seen across the examined coccolithophore species, including the cell signalling 14-3-3 domain, chromosome segregation SMC ATPase domain, as well as proteins involved in protein processing and protease inhibition. The copper-binding cupredoxin domain was observed in both Gephyrocapsa species, as well as other marine calcifiers, suggestive of a requirement of Cu in biomineralisation. Building consensus with existing work, we highlight the pentapeptide repeat as a feature which is associated with the coccolith matrix, being identified in all three examined species, and propose that this structural motif may play a role in controlling coccolith growth. This preliminary study provides insight towards the functional diversity of calcification machinery in coccolithophores and presents a number of candidates for future research towards understanding the biochemical controls which direct coccolithogenesis.
颗石藻是海洋碳循环的主要组成部分。这些单细胞藻类产生由碳酸钙构成的华丽结构，称为颗石，约占公海中方解石产量的50%。指导和控制颗石形成的确切分子机制尚不清楚。在本研究中，我们报告了一系列颗石藻模型物种所产生的颗石内蛋白质的存在情况和功能特征，这些物种包括：全球分布广泛且研究充分的赫氏颗石藻（原艾氏颗石藻）以及相关的大洋颗石藻，还有体型更大、钙化程度更高的布氏颗石藻。我们比较了不同物种之间的蛋白质特征，并与先前在其他海洋钙化生物中鉴定出的生物矿化蛋白进行了对比。值得注意的是，在所研究的颗石藻物种中一致观察到了几种蛋白质特征，包括细胞信号转导14-3-3结构域、染色体分离SMC ATP酶结构域，以及参与蛋白质加工和蛋白酶抑制的蛋白质。在赫氏颗石藻属的两个物种以及其他海洋钙化生物中都观察到了铜结合型质体蓝素结构域，这表明生物矿化过程中需要铜。结合现有研究成果，我们强调五肽重复序列是与颗石基质相关的一个特征，在所有三个被研究物种中都有发现，并提出这个结构基序可能在控制颗石生长中发挥作用。这项初步研究为了解颗石藻钙化机制的功能多样性提供了见解，并为未来研究指导颗石形成的生化控制提供了一些候选对象。
