TY - JOUR
T1 - Salt Triggers the Simple Coacervation of an Underwater Adhesive When Cations Meet Aromatic π Electrons in Seawater
AU - Kim, Sangsik
AU - Yoo, Hee Young
AU - Huang, Jun
AU - Lee, Yongjin
AU - Park, Sohee
AU - Park, Yeonju
AU - Jin, Sila
AU - Jung, Young Mee
AU - Zeng, Hongbo
AU - Hwang, Dong Soo
AU - Jho, Yongseok
N1 - Publisher Copyright:
© 2017 American Chemical Society.
PY - 2017/7/25
Y1 - 2017/7/25
N2 - 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.
AB - 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.
KW - cation-π interaction
KW - mfp-1
KW - protein droplet
KW - simple coacervation
KW - surface forces apparatus
UR - http://www.scopus.com/inward/record.url?scp=85026286826&partnerID=8YFLogxK
U2 - 10.1021/acsnano.7b01370
DO - 10.1021/acsnano.7b01370
M3 - Article
C2 - 28614666
AN - SCOPUS:85026286826
SN - 1936-0851
VL - 11
SP - 6764
EP - 6772
JO - ACS Nano
JF - ACS Nano
IS - 7
ER -