Evolutionary patterns of proteinase activity in attine ant fungus gardens
Evolutionary patterns of proteinase activity in attine ant fungus gardens
复制标题
蚂蚁真菌园蛋白酶活性的进化模式
作者：
T. A. Semenova;D. Hughes;J. Boomsma;M. Schiøtt
背景蚂蚁与担子菌共生，担子菌生长在植物材料的基质上。这种间接的食草性意味着共生很可能是缺氮的，因此可能已经进化出特定的机制来提高蛋白质的可获得性。结果我们测定了巴拿马产真菌蚂蚁的14种8属14种真菌花园的广泛pH范围内的蛋白酶活性。我们将这些活性图谱绘制在一个独立获得的共生体的分子系统发育图上，结果表明，低属性共生体的总蛋白水解酶活性在ph6左右达到峰值。没有已知的自由生活近亲的高属性共生体的蛋白酶活性远远高于低属性共生体。它们的总体外蛋白酶活性在pH值为5时达到峰值，接近蚂蚁在真菌花园中保持的pH值，这表明真菌蛋白酶的最适pH可能在进化的更多真菌共生体不可逆驯化后发生了变化。真菌花园在pH 5.2时的缓冲能力非常高，这也支持了这一观点，并表明真菌共生体积极地帮助将花园的酸度保持在这一特定的水平。金属蛋白水解酶的活性主要分布在较低等级花园，因此可能代表了蛋白酶产生的祖先类型，而丝氨酸蛋白酶活性主导了由Trachymyrmex和Sericmyrmex饲养的较高等级花园的活性分布，这表明这些酶类的产生可能存在权衡。值得注意的是，ATTA和Acromyrmex切叶蚂蚁树冠类物种共有的单一共生体大多具有金属蛋白酶活性，这表明在真菌-花园共生体的驯化历史中，酶的产生可能发生了周期性的变化。结论真菌共生体的蛋白酶最适pH和缓冲能力似乎进化出了显著的适应与耕作蚂蚁专有共生的能力。尽管丝氨酸和金属蛋白酶在真菌花园中的功能作用尚不清楚，但这两类蛋白水解酶的不同产生表明底物专一性可能是重要的，权衡可能会阻止这两类酶的同时上调。
BackgroundAttine ants live in symbiosis with a basidiomycetous fungus that they rear on a substrate of plant material. This indirect herbivory implies that the symbiosis is likely to be nitrogen deprived, so that specific mechanisms may have evolved to enhance protein availability. We therefore hypothesized that fungal proteinase activity may have been under selection for efficiency and that different classes of proteinases might be involved.ResultsWe determined proteinase activity profiles across a wide pH range for fungus gardens of 14 Panamanian species of fungus-growing ants, representing eight genera. We mapped these activity profiles on an independently obtained molecular phylogeny of the symbionts and show that total proteinase activity in lower attine symbionts peaks at ca. pH 6. The higher attine symbionts that have no known free-living relatives had much higher proteinase activities than the lower attine symbionts. Their total in vitro proteinase activity peaked at pH values around 5, which is close to the pH that the ants maintain in their fungus gardens, suggesting that the pH optimum of fungal proteinases may have changed after the irreversible domestication of evolutionary more derived fungal symbionts. This notion is also supported by buffering capacities of fungus gardens at pH 5.2 being remarkably high, and suggests that the fungal symbiont actively helps to maintain garden acidity at this specific level. Metalloproteinases dominated the activity profiles of lower attine gardens and may thus represent the ancestral type of proteinase production, whereas serine proteinase activity dominated the activity profiles of the higher attine gardens reared by Trachymyrmex and Sericomyrmex, suggesting that there may be trade-offs in the production of these enzyme classes. Remarkably, the single symbiont that is shared by species of the crown group of Atta and Acromyrmex leaf-cutting ants mostly showed metalloproteinase activity, suggesting that recurrent changes in enzyme production may have occurred throughout the domestication history of fungus-garden symbionts.ConclusionsProteinase pH optima and buffering capacities of fungal symbionts appear to have evolved remarkable adaptations to living in obligate symbiosis with farming ants. Although the functional roles of serine and metalloproteinases in fungus gardens are unknown, the differential production of these classes of proteolytic enzymes suggest that substrate specificity may be important and that trade-offs may prevent the simultaneous upregulation of both classes of enzymes.
DNA 序列分析。
影响因子：
2.3
作者：
Weir,BS
通讯作者：
Weir,BS