Silica Condensation by a Silicatein α Homologue Involves Surface-Induced Transition to a Stable Structural Intermediate Forming a Saturated Monolayer

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• 作者：Siddharth V. Patwardhan ; Stephen A. Holt ; Sharon M. Kelly ; Michaela Kreiner ; Carole C. Perry ; Christopher F. van der Walle
• 刊名：Biomacromolecules
• 出版年：2010
• 出版时间：November 8, 2010
• 年：2010
• 卷：11
• 期：11
• 页码：3126-3135
• 全文大小：433K
• 年卷期：v.11,no.11(November 8, 2010)
• ISSN：1526-4602

文摘

Silicatein α exists within the protein filament of silica spicules of the marine sponge Tethya aurantium in a predominantly β-sheet structure. However, it is produced in a soluble form with mixed α-helix/β-sheet structure akin to its cathepsin L homologue. To understand this conformational transition in the context of enzyme catalyzed silica condensation, we used a functional, recombinant silicatein α termed 4SER. In solution, 4SER becomes conformationally unstable at pH 7 and readily unfolds to a soluble β-sheet intermediate, losing the majority of its helical structure. This β-sheet intermediate is present following adsorption of 4SER to a silica surface from solution. 4SER is particularly surface active, forming a near saturated monolayer on SiO₂ from low bulk concentrations, without transition to multilayers at high bulk concentrations. The adsorbed intermediate remains stable during silica condensation and drying. We propose that the β-sheet structure for silicatein α in marine sponge spicules represents a stable structural intermediate, formed upon adsorption to the silica surface.