Investigating the Effect of Membrane Composition on the Selective Ammonium Transport of E. coli AmtB Membrane Proteins

Selective membrane separation processes can recover ammonia from wastewaters and advance a circular nutrient economy. E. coli AmtB (EcAmtB) is a well-characterized and ammonium-selective membrane protein that could be embedded into synthetic membranes. However, the effects of phospholipids present in E. coli membranes, namely 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG), on EcAmtB folding and function remain undetermined. Solid-supported membrane-based electrophysiology (SSME) was conducted to observe ammonium migration through EcAmtB proteoliposomes containing varying compositions of phospholipids POPE, POPG, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphate (POPA). In contrast to previous reports highlighting the singular importance of POPG for ammonia transport, this study found that proteoliposomes containing POPE adhered to SSME sensors exhibited the highest total ammonium permeability (2498 pA of total sensor current or 15.59 billion cations per second). A crucial phospholipid head group bonding site may be the E70 location, a glutamate at the junction of two protein subunits. Understanding how phospholipid-protein bonding determines transport performance can aid in developing similar protein-synthetic membrane bonding structures for industrial selective recovery processes.