Interfacial self-assembly of a bacterial hydrophobin
Interfacial self-assembly of a bacterial hydrophobin
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DOI：
10.1073/pnas.1419016112
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发表时间：
2015-04-28
影响因子：
11.1
通讯作者：
MacPhee, Cait. E.
中科院分区：
文献类型：
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作者：
Bromley, Keith M.;Morris, Ryan J.;MacPhee, Cait. E.
自然环境中的大多数细菌都生活在生物膜的范围内。革兰氏阳性细菌枯草芽孢杆菌形成生物膜，其表现出特征性的褶皱形态和高度疏水的表面。产生这些特性的一个关键成分是蛋白质BslA，它在固着群落的表面形成一层涂层。我们最近报道了BslA的结构，并注意到存在一个大的表面暴露的疏水补丁。这样的表面补丁也被观察到的表面活性蛋白类称为疏水蛋白，并被认为是介导其界面活性。然而，虽然功能相关的疏水蛋白，BslA股没有序列也没有结构相似性，在这里，我们表明，作用机制也是不同的。具体而言，我们的研究结果表明，氨基酸组成的大，表面暴露的疏水帽在晶体结构中被屏蔽在水溶液中通过采用无规卷曲构象，使蛋白质是可溶性的和单体。在界面处，这些帽残基重新折叠，将疏水侧链插入空气或油相中并形成三链β-折叠。然后，这种形式自组装成一个有序的2D矩形晶格，使界面稳定。通过用带正电荷的赖氨酸取代帽中心的疏水性亮氨酸，我们改变了吸附的能量学并破坏了2D晶格的形成。这种有限的结构变态代表了一种以前未识别的环境响应机制，用于蛋白质的界面稳定。
The majority of bacteria in the natural environment live within the confines of a biofilm. The Gram-positive bacterium Bacillus subtilis forms biofilms that exhibit a characteristic wrinkled morphology and a highly hydrophobic surface. A critical component in generating these properties is the protein BslA, which forms a coat across the surface of the sessile community. We recently reported the structure of BslA, and noted the presence of a large surface-exposed hydrophobic patch. Such surface patches are also observed in the class of surface-active proteins known as hydrophobins, and are thought to mediate their interfacial activity. However, although functionally related to the hydrophobins, BslA shares no sequence nor structural similarity, and here we show that the mechanism of action is also distinct. Specifically, our results suggest that the amino acids making up the large, surface-exposed hydrophobic cap in the crystal structure are shielded in aqueous solution by adopting a random coil conformation, enabling the protein to be soluble and monomeric. At an interface, these cap residues refold, inserting the hydrophobic side chains into the air or oil phase and forming a three-stranded beta-sheet. This form then self-assembles into a well-ordered 2D rectangular lattice that stabilizes the interface. By replacing a hydrophobic leucine in the center of the cap with a positively charged lysine, we changed the energetics of adsorption and disrupted the formation of the 2D lattice. This limited structural metamorphosis represents a previously unidentified environmentally responsive mechanism for interfacial stabilization by proteins.