Daminova Amina G, Rassabina Anna E, Khabibrakhmanova Venera R, Burygin Gennady L, Beckett Richard P, Minibayeva Farida V
Kazan Institute of Biochemistry and Biophysics, Federal Research Center Kazan Scientific Center of the Russian Academy of Sciences, 2/31, Lobachevsky Str., Kazan 420111, Russia.
Institute of Biochemistry and Physiology of Plants and Microorganisms, Saratov Scientific Centre of the Russian Academy of Sciences, 13 Prospect Entuziastov, Saratov 410049, Russia.
Mycologia. 2025 Jul-Aug;117(4):629-639. doi: 10.1080/00275514.2025.2493364. Epub 2025 May 23.
Melanins are the pigments with diverse protective functions in a wide range of organisms. The ability of lichens to synthesize melanins is an important adaptation in response to adverse light conditions, including ultraviolet (UV) irradiation and high light. Previously, we demonstrated that melanization of the lichen is accompanied by the accumulation of melanin granules in the upper cortex. However, very little information is available on the morphology and physicochemical properties of these particles. Here, for the first time, we used polyclonal antibodies against eumelanin to visualize melanin in the upper cortex of and confirm its identity. Using scanning electron microscopy, we showed that extracted melanins are large, spherical aggregates, with an average size of 230 nm. The aggregates had an irregular and unstable structure and displayed high adhesive properties, according to atomic force microscopy. Purification using size exclusion chromatography showed that melanins coeluted with polysaccharides. Purified particles were visualized as discrete structures (subaggregates) with an average size of 42 nm and displayed higher stability and lower adhesive properties than non-purified aggregates. In colloidal aqueous systems, melanin particles formed aggregates with particle sizes of 279 and 212 nm for the non-purified and purified samples, respectively, suggesting that the removal of the polysaccharide component during purification causes the condensation of the polyaromatic structure of melanin. Taken together, our results suggest that melanin particles extracted from UV-melanized thalli of the lichen comprise a supramolecular assembly of melanin and polysaccharides. Analysis of the size, ζ-potential, and polydispersity index suggests that melanin particles are capable of structural rearrangements that lead to changes in their nanomechanical properties. The ability of the melanin to bind to polysaccharides may enhance the structural robustness of mycobiont cell walls and increase the tolerance of lichen thalli to stressful environments.
黑色素是在多种生物体中具有多种保护功能的色素。地衣合成黑色素的能力是对包括紫外线（UV）照射和强光在内的不利光照条件的重要适应。此前，我们证明地衣的黑化伴随着黑色素颗粒在上皮层的积累。然而，关于这些颗粒的形态和物理化学性质的信息非常少。在这里，我们首次使用针对真黑色素的多克隆抗体来可视化地衣上层皮层中的黑色素并确认其身份。通过扫描电子显微镜，我们发现提取的黑色素是大的球形聚集体，平均尺寸为230纳米。根据原子力显微镜，这些聚集体具有不规则和不稳定的结构，并表现出高粘附性。使用尺寸排阻色谱法纯化表明，黑色素与多糖共洗脱。纯化后的颗粒呈现为平均尺寸为42纳米的离散结构（亚聚集体），并且与未纯化的聚集体相比显示出更高的稳定性和更低的粘附性。在胶体水体系中，非纯化和纯化样品的黑色素颗粒分别形成粒径为279和212纳米的聚集体，这表明纯化过程中多糖成分的去除导致黑色素多芳结构的凝聚。综上所述，我们的结果表明，从地衣紫外线黑化的叶状体中提取的黑色素颗粒包含黑色素和多糖的超分子组装体。对尺寸、ζ电位和多分散指数的分析表明，黑色素颗粒能够进行结构重排，从而导致其纳米力学性质发生变化。黑色素与多糖结合的能力可能会增强菌根细胞壁的结构稳健性，并增加地衣叶状体对压力环境的耐受性。
