Department of Chemical and Materials Engineering, University of Alberta , Edmonton, AB T6G 2 V4, Canada.
Asia Pacific Center for Theoretical Physics , Pohang 37673, Republic of Korea.
ACS Nano. 2017 Jul 25;11(7):6764-6772. doi: 10.1021/acsnano.7b01370. Epub 2017 Jun 20.
Adhesive systems in many marine organisms are postulated to form complex coacervates (liquid-liquid phase separation) through a process involving oppositely charged polyelectrolytes. Despite this ubiquitous speculation, most well-characterized mussel adhesive proteins are cationic and polyphenolic, and the pursuit of the negatively charged proteins required for bulk complex coacervation formation internally remains elusive. In this study, we provide a clue for unraveling this paradox by showing the bulky fluid/fluid separation of a single cationic recombinant mussel foot protein, rmfp-1, with no additional anionic proteins or artificial molecules, that is triggered by a strong cation-π interaction in natural seawater conditions. With the similar condition of salt concentration at seawater level (>0.7 M), the electrostatic repulsion between positively charged residues of mfp-1 is screened significantly, whereas the strong cation-π interaction remains unaffected, which leads to the macroscopic phase separation (i.e., bulky coacervate formation). The single polyelectrolyte coacervate shows interesting mechanical properties including low friction, which facilitates the secretion process of the mussel. Our findings reveal that the cation-π interaction modulated by salt is a key mechanism in the mussel adhesion process, providing new insights into the basic understanding of wet adhesion, self-assembly processes, and biological phenomena that are mediated by strong short-range attractive forces in water.
许多海洋生物中的黏附系统被假定通过涉及带相反电荷的聚电解质的过程形成复杂凝聚物（液-液相分离）。尽管存在这种普遍的推测，但大多数特征明确的贻贝黏附蛋白是阳离子和多酚，并且内部形成大块复杂凝聚物所需的带负电荷的蛋白质的追求仍然难以捉摸。在这项研究中，我们通过展示单一阳离子重组贻贝足蛋白 rmfp-1 的大量流体/流体分离来提供解决此悖论的线索，而无需额外的阴离子蛋白或人工分子，这是由天然海水中的强阳离子-π 相互作用触发的。在类似的盐浓度条件（高于 0.7 M）下，mfp-1 上带正电荷残基之间的静电排斥作用被显著屏蔽，而强阳离子-π 相互作用不受影响，导致宏观相分离（即大量凝聚物形成）。单一聚电解质凝聚物表现出有趣的机械性能，包括低摩擦，这有利于贻贝的分泌过程。我们的发现表明，盐调制的阳离子-π 相互作用是贻贝黏附过程的关键机制，为基本理解湿黏附、自组装过程以及在水中由强短程吸引力介导的生物现象提供了新的见解。
