Ghrayeb Mnar, Hayet Shahar, Lester-Zer Neta, Levi-Kalisman Yael, Chai Liraz
Institute of Chemistry, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Jerusalem 91904, Israel.
The Center for Nanoscience and Nanotechnology, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Jerusalem 91904, Israel.
Microorganisms. 2021 Mar 4;9(3):529. doi: 10.3390/microorganisms9030529.
Functional amyloid proteins often appear as fibers in extracellular matrices of microbial soft colonies. In contrast to disease-related amyloid structures, they serve a functional goal that benefits the organism that secretes them, which is the reason for the title "functional". Biofilms are a specific example of a microbial community in which functional amyloid fibers play a role. Functional amyloid proteins contribute to the mechanical stability of biofilms and mediate the adhesion of the cells to themselves as well as to surfaces. Recently, it has been shown that functional amyloid proteins also play a regulatory role in biofilm development. TasA is the major proteinaceous fibrilar component of the extracellular matrix of biofilms made of the soil bacterium and Gram-positive . We have previously shown, as later corroborated by others, that in acidic solutions, TasA forms compact aggregates that are composed of tangled fibers. Here, we show that in a neutral pH and above a certain TasA concentration, the fibers of TasA are elongated and straight and that they bundle up in highly concentrated salt solutions. TasA fibers resemble the canonic amyloid morphology; however, these fibers also bear an interesting nm-scale periodicity along the fiber axis. At the molecular level, TasA fibers contain a twisted β-sheet structure, as indicated by circular dichroism measurements. Our study shows that the morphology of TasA fibers depends on the environmental conditions. Different fibrilar morphologies may be related with different functional roles in biofilms, ranging from granting biofilms with a mechanical support to acting as antibiotic agents.
功能性淀粉样蛋白通常以纤维形式出现在微生物软菌落的细胞外基质中。与疾病相关的淀粉样结构不同，它们具有功能性目标，对分泌它们的生物体有益，这就是“功能性”这一名称的由来。生物膜是微生物群落的一个具体例子，其中功能性淀粉样纤维发挥作用。功能性淀粉样蛋白有助于生物膜的机械稳定性，并介导细胞与自身以及与表面的粘附。最近，研究表明功能性淀粉样蛋白在生物膜发育中也发挥调节作用。TasA是由土壤细菌和革兰氏阳性菌形成的生物膜细胞外基质的主要蛋白质纤维成分。我们之前已经表明，正如其他人后来所证实的那样，在酸性溶液中，TasA会形成由缠结纤维组成的紧密聚集体。在这里，我们表明在中性pH值及高于一定TasA浓度的情况下，TasA纤维会伸长并变直，并且它们在高浓度盐溶液中会聚集在一起。TasA纤维类似于典型的淀粉样形态；然而，这些纤维在纤维轴向上还具有有趣的纳米级周期性。在分子水平上，圆二色性测量表明TasA纤维含有扭曲的β-折叠结构。我们的研究表明，TasA纤维的形态取决于环境条件。不同的纤维形态可能与生物膜中的不同功能作用有关，从为生物膜提供机械支持到充当抗生素。
