Uncovering the membrane and pore formation mechanisms of the lysozyme membrane made via the amyloid-like assembly

Biomimetic protein membranes have attracted increasing interests because of their distinctive separation properties in the membrane field. Low-cost and stable protein lysozyme has been intensively invetigated to fabricate high-performance sepration membranes via a facile and scalable method of amyloid-like assembly. However, the pore formation mechnism of the lysozyme membrane remains unclear. Herein, the lysozyme membranes were fabricated and the membrane formation mechnism and separation properties were investigated experimentally. Molecular dynamics simulation (MDS) was also employed to reveal the pore formation mechanism of the lysozyme membrane. The fabricated lysozyme membrane achieved a stable high water permeance of 10.2 L m-2 h-1 bar-1, as well as a relatively high separation factor (9.5) towards antibiotic and sodium chloride. MDS results found that the membrane pore size is governed by the amino acid compositions and is negatively dependent on the intermolecular forces among amino acids around the pores. Selective pores with 0.54 nm in diameter are primarily formed by these amino acids including alanine (35%), aspartic acid (25%), arginine (15%), phenylalanine (11%), and lysine (7%), in which half of them have hydrophobic side chains with no charge, and another half have hydrophilic side chains with balanced charges. This work may stimulate the development of highly permeable and selective protein membranes by carefully engineering their amino acid compositions with optimal charges and hydrophobicity for generation of numerous selective pores.