Bioinformatics classification of the MgtE Mg2 + channel and de novo protein design for the stabilization of its novel subclass

Abstract

MgtE channels play crucial roles in Mg²⁺ homeostasis and are implicated in bacterial survival under antibiotic exposure. Previous structural and biophysical studies have focused predominantly on Thermus thermophilus MgtE, leaving the structural and mechanistic diversity of MgtE family proteins largely unexplored. In this study, via a genome mining approach, we identify diverse MgtE homologs, including a novel subclass termed the “mini-N type,” which lacks the canonical cytoplasmic N and CBS domains but possesses a unique small N-like domain. Despite extensive expression screening, mini-N-type homologs cannot be stably purified. To address this issue, we design a series of de novo proteins and determine their crystal structures. A selected de novo protein is fused to a mini-N-type MgtE, enabling successful purification and preliminary cryo-EM imaging. Our findings demonstrate that de novo-designed protein fusions serve as powerful tools for stabilizing and purifying otherwise unstable membrane proteins, opening new avenues for structural and functional studies of otherwise inaccessible membrane proteins.