Huang Yujian, Wang Yongzhong, Tan Li, Sun Leming, Petrosino Jennifer, Cui Mei-Zhen, Hao Feng, Zhang Mingjun
Department of Biomedical Engineering, College of Engineering, The Ohio State University, Columbus, OH 43210; Interdisciplinary Biophysics Graduate Program, The Ohio State University, Columbus, OH 43210; Dorothy M. Davis Heart & Lung Research Institute, The Ohio State University Wexner Medical Center, Columbus, OH 43210;
Complex Carbohydrate Research Center, University of Georgia, Athens, GA 30602; DOE BioEnergy Science Center, University of Georgia, Athens, GA 30602;
Proc Natl Acad Sci U S A. 2016 Jun 7;113(23):E3193-202. doi: 10.1073/pnas.1600406113. Epub 2016 May 23.
Over 130 y have passed since Charles Darwin first discovered that the adventitious roots of English ivy (Hedera helix) exude a yellowish mucilage that promotes the capacity of this plant to climb vertical surfaces. Unfortunately, little progress has been made in elucidating the adhesion mechanisms underlying this high-strength adhesive. In the previous studies, spherical nanoparticles were observed in the viscous exudate. Here we show that these nanoparticles are predominantly composed of arabinogalactan proteins (AGPs), a superfamily of hydroxyproline-rich glycoproteins present in the extracellular spaces of plant cells. The spheroidal shape of the AGP-rich ivy nanoparticles results in a low viscosity of the ivy adhesive, and thus a favorable wetting behavior on the surface of substrates. Meanwhile, calcium-driven electrostatic interactions among carboxyl groups of the AGPs and the pectic acids give rise to the cross-linking of the exuded adhesive substances, favor subsequent curing (hardening) via formation of an adhesive film, and eventually promote the generation of mechanical interlocking between the adventitious roots of English ivy and the surface of substrates. Inspired by these molecular events, a reconstructed ivy-mimetic adhesive composite was developed by integrating purified AGP-rich ivy nanoparticles with pectic polysaccharides and calcium ions. Information gained from the subsequent tensile tests, in turn, substantiated the proposed adhesion mechanisms underlying the ivy-derived adhesive. Given that AGPs and pectic polysaccharides are also observed in bioadhesives exuded by other climbing plants, the adhesion mechanisms revealed by English ivy may forward the progress toward understanding the general principles underlying diverse botanic adhesives.
自查尔斯·达尔文首次发现常春藤（洋常春藤）的不定根会分泌出一种淡黄色黏液，这种黏液能增强该植物攀爬垂直表面的能力以来，已经过去了130多年。遗憾的是，在阐明这种高强度粘合剂的粘附机制方面进展甚微。在之前的研究中，在粘性分泌物中观察到了球形纳米颗粒。在此我们表明，这些纳米颗粒主要由阿拉伯半乳聚糖蛋白（AGPs）组成，AGPs是一类富含羟脯氨酸的糖蛋白超家族，存在于植物细胞的胞外空间。富含AGP的常春藤纳米颗粒的球形形状导致常春藤粘合剂的低粘度，从而在基材表面具有良好的润湿行为。同时，AGPs的羧基与果胶酸之间由钙驱动的静电相互作用导致分泌的粘性物质交联，有利于随后通过形成粘附膜进行固化（硬化），最终促进常春藤不定根与基材表面之间产生机械互锁。受这些分子事件的启发，通过将纯化的富含AGP的常春藤纳米颗粒与果胶多糖和钙离子整合，开发了一种仿生常春藤粘附复合材料。随后拉伸试验获得的信息反过来证实了所提出的常春藤衍生粘合剂的粘附机制。鉴于在其他攀缘植物分泌的生物粘合剂中也观察到了AGPs和果胶多糖，常春藤揭示的粘附机制可能会推动我们在理解各种植物粘合剂基本原理方面取得进展。
