Ricca John G, Petersen Holly A, Grosvirt-Dramen Adam, Mayali Xavier, Naylon Sarah H, Duersch Bobby G, Dufresne Craig P, Weber Peter K, Sonani Ravi R, Prevelige Peter E, Hochbaum Allon I, Merk Vivian, Louda J W, Wang Fengbin
Department of Chemistry and Biochemistry, Florida Atlantic University, Boca Raton, FL, USA.
Center for Environmental Studies, Florida Atlantic University, Davie, FL, USA.
Nat Commun. 2025 Aug 29;16(1):8082. doi: 10.1038/s41467-025-63379-1.
Cyanobacteria are vital photosynthetic prokaryotes, but some form harmful algal blooms (cyanoHABs) that disrupt ecosystems and produce toxins. The mechanisms by which these blooms form have yet to be fully understood, particularly the role of extracellular components. Here, we present a 2.4 Å cryo-EM structure of a pilus, termed the cyanobacterial tubular (CT) pilus, found in the cyanoHAB-forming Microcystis aeruginosa. The pilin exhibits a unique protein fold, forming a tubular pilus structure with tight, double-layer anti-parallel β-sheet interactions. We show that CT pili are essential for buoyancy by facilitating the formation of micro-colonies, which increases drag force and prevents sinking. The CT pilus surface is heavily glycosylated with ten monosaccharide modifications per pilin. Furthermore, CT pili can enrich microcystin, potentially enhancing cellular resilience, and co-localize with iron-enriched extracellular matrix components. Thus, we propose that this pilus plays an important role in the proliferation of cyanoHABs. This just discovered pilus family appears to be widely distributed across several cyanobacterial orders. Our structural and functional characterization of CT pili provide insights into cyanobacterial cell morphology, physiology, and toxin interactions, and identify potential targets for disrupting bloom formation.
蓝藻是重要的光合原核生物，但有些会形成有害藻华（蓝藻藻华），破坏生态系统并产生毒素。这些藻华形成的机制尚未完全了解，尤其是细胞外成分的作用。在这里，我们展示了一种菌毛的2.4埃冷冻电镜结构，称为蓝藻管状（CT）菌毛，它存在于形成蓝藻藻华的铜绿微囊藻中。菌毛蛋白呈现出独特的蛋白质折叠方式，形成具有紧密的双层反平行β-折叠相互作用的管状菌毛结构。我们表明，CT菌毛通过促进微菌落的形成对浮力至关重要，这会增加拖曳力并防止下沉。CT菌毛表面高度糖基化，每个菌毛蛋白有十种单糖修饰。此外，CT菌毛可以富集微囊藻毒素，可能增强细胞恢复力，并与富含铁的细胞外基质成分共定位。因此，我们提出这种菌毛在蓝藻藻华的增殖中起重要作用。这个刚发现的菌毛家族似乎广泛分布于几个蓝藻目。我们对CT菌毛的结构和功能表征为蓝藻细胞形态、生理学和毒素相互作用提供了见解，并确定了破坏藻华形成的潜在靶点。
