Kwan Ann H, Macindoe Ingrid, Vukasin Paul V, Morris Vanessa K, Kass Itamar, Gupte Rima, Mark Alan E, Templeton Matthew D, Mackay Joel P, Sunde Margaret
School of Molecular and Microbial Biosciences, University of Sydney, Sydney, New South Wales 2006, Australia.
J Mol Biol. 2008 Oct 10;382(3):708-20. doi: 10.1016/j.jmb.2008.07.034. Epub 2008 Jul 22.
Class I hydrophobins are fungal proteins that self-assemble into robust amphipathic rodlet monolayers on the surface of aerial structures such as spores and fruiting bodies. These layers share many structural characteristics with amyloid fibrils and belong to the growing family of functional amyloid-like materials produced by microorganisms. Although the three-dimensional structure of the soluble monomeric form of a class I hydrophobin has been determined, little is known about the molecular structure of the rodlets or their assembly mechanism. Several models have been proposed, some of which suggest that the Cys3-Cys4 loop has a critical role in the initiation of assembly or in the polymeric structure. In order to provide insight into the relationship between hydrophobin sequence and rodlet assembly, we investigated the role of the Cys3-Cys4 loop in EAS, a class I hydrophobin from Neurospora crassa. Remarkably, deletion of up to 15 residues from this 25-residue loop does not impair rodlet formation or reduce the surface activity of the protein, and the physicochemical properties of rodlets formed by this mutant are indistinguishable from those of its full-length counterpart. In addition, the core structure of the truncation mutant is essentially unchanged. Molecular dynamics simulations carried out on the full-length protein and this truncation mutant binding to an air-water interface show that, although it is hydrophobic, the loop does not play a role in positioning the protein at the surface. These results demonstrate that the Cys3-Cys4 loop does not have an integral role in the formation or structure of the rodlets and that the major determinant of the unique properties of these proteins is the amphipathic core structure, which is likely to be preserved in all hydrophobins despite the high degree of sequence variation across the family.
I类疏水蛋白是真菌蛋白，可在孢子和子实体等气生结构表面自组装成坚固的两亲性小杆单层。这些层与淀粉样纤维具有许多结构特征，属于微生物产生的功能性淀粉样蛋白材料这一不断增长大家族的成员。尽管已确定I类疏水蛋白可溶性单体形式的三维结构，但对于小杆的分子结构或其组装机制知之甚少。已经提出了几种模型，其中一些表明Cys3 - Cys4环在组装起始或聚合物结构中起关键作用。为了深入了解疏水蛋白序列与小杆组装之间的关系，我们研究了粗糙脉孢菌的I类疏水蛋白EAS中Cys3 - Cys4环的作用。值得注意的是，从这个25个残基的环中删除多达15个残基不会损害小杆的形成或降低蛋白质的表面活性，并且由该突变体形成的小杆的物理化学性质与其全长对应物的性质无法区分。此外，截短突变体的核心结构基本不变。对全长蛋白和该截短突变体与空气 - 水界面结合进行的分子动力学模拟表明，尽管该环具有疏水性，但它在将蛋白质定位在表面上不起作用。这些结果表明，Cys3 - Cys4环在小杆的形成或结构中不具有不可或缺的作用，并且这些蛋白质独特性质的主要决定因素是两亲性核心结构，尽管整个家族的序列变异程度很高，但该结构可能在所有疏水蛋白中都得以保留。
