Following fungal melanin biosynthesis with solid-state NMR: biopolymer molecular structures and possible connections to cell-wall polysaccharides.
Following fungal melanin biosynthesis with solid-state NMR: biopolymer molecular structures and possible connections to cell-wall polysaccharides.
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DOI：
10.1021/bi702093r
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发表时间：
2008-03
期刊：
影响因子：
2.9
通讯作者：
Junyan Zhong;S. Frases;Hsin Wang;A. Casadevall;R. Stark
中科院分区：
文献类型：
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作者：
Junyan Zhong;S. Frases;Hsin Wang;A. Casadevall;R. Stark
黑色素在动植物中具有多种保护功能，但在新生隐球菌等真菌中，黑色素也与毒力有关。最近开发的一种固体核磁共振(NMR)策略，基于在黑色素中加入特定的(13)C富集物前体，随后对粉状和溶剂型黑色素幽灵进行光谱分析，提供了对真菌黑色素生物合成的新的分子水平的见解。L-多巴前体的侧链在新生葡萄球菌黑色素中环化并形成吲哚结构，芳环的修饰揭示了生物聚合物中可能的聚合物链延长和交联模式。在生长介质中提供的甘露糖即使经过彻底降解和透析处理后仍以β-吡喃糖的形式保留在黑色素幽灵中，这表明色素可能被紧密结合或共价结合到多糖类真菌细胞壁。相比之下，葡萄糖在代谢过程中被扰乱，并结合到黑色素幽灵中存在的多糖细胞壁和脂肪链中，这与作为细胞营养物质的代谢用途以及与色素的共价结合一致。先前报道的几种真菌黑色素中显著的脂肪族基团被鉴定为甘油三酯结构，可能具有一个或多个链不饱和部位。这些结果表明真菌黑色素含有来自L多巴聚合以外的其他来源的化学成分，并表明L多巴产物与多糖组分之间的共价键可能有助于将这种色素附着在细胞壁结构上。
Melanins serve a variety of protective functions in plants and animals, but in fungi such as Cryptococcus neoformans they are also associated with virulence. A recently developed solid-state nuclear magnetic resonance (NMR) strategy, based on the incorporation of site-specific (13)C-enriched precursors into melanin, followed by spectroscopy of both powdered and solvent-swelled melanin ghosts, was used to provide new molecular-level insights into fungal melanin biosynthesis. The side chain of an l-dopa precursor was shown to cyclize and form a proposed indole structure in C. neoformans melanin, and modification of the aromatic rings revealed possible patterns of polymer chain elongation and cross-linking within the biopolymer. Mannose supplied in the growth medium was retained as a beta-pyranose moiety in the melanin ghosts even after exhaustive degradative and dialysis treatments, suggesting the possibility of tight binding or covalent incorporation of the pigment into the polysaccharide fungal cell walls. In contrast, glucose was scrambled metabolically and incorporated into both polysaccharide cell walls and aliphatic chains present in the melanin ghosts, consistent with metabolic use as a cellular nutrient as well as covalent attachment to the pigment. The prominent aliphatic groups reported previously in several fungal melanins were identified as triglyceride structures that may have one or more sites of chain unsaturation. These results establish that fungal melanin contains chemical components derived from sources other than l-dopa polymerization and suggest that covalent linkages between l-dopa-derived products and polysaccharide components may serve to attach this pigment to cell wall structures.