Scientists Discover New 'Superfamily' of Bacterial Proteins with Unique Lipid-Trapping Abilities

Scientists have uncovered a new type of protein in bacteria that significantly expands our understanding of how these microorganisms interact with their surroundings. Published in Nature Communications, the study focuses on a protein called PopA, which is found in the bacterial predator Bdellovibrio bacteriovorus. PopA forms a unique fivefold structure, setting it apart from the typical single or three-part structures observed in similar proteins. An international research team, led by scientists at the University of Birmingham, employed advanced imaging techniques to reveal that PopA has a bowl-like shape capable of trapping parts of the bacterial membrane. When PopA—an outer membrane protein (OMP)—is introduced into E. coli bacteria, it causes membrane damage, suggesting that the protein plays a crucial role in how Bdellovibrio attacks and consumes other bacteria. Further structural analysis and AI-driven searches revealed that PopA homologs, found across various bacterial species, can form tetramers, hexamers, and nonamers, all of which share the distinctive lipid-trapping feature. This finding indicates the existence of a widespread, previously unrecognized "superfamily" of proteins. Professor Andrew Lovering, the lead author from the University of Birmingham, explained, "Our discovery challenges the conventional wisdom about bacterial proteins. The unique structure and function of PopA suggest that bacteria have more intricate mechanisms of environmental interaction than previously believed. This could pave the way for new approaches in targeting harmful bacteria, with significant implications for medicine and biotechnology." The research also identified a second family of proteins that form ring-like structures, further broadening our knowledge of bacterial protein diversity. Using a combination of X-ray crystallography, cryo-electron microscopy, and molecular dynamics, the team showed that PopA, previously known as Bd0427, includes a central lipid-trapping cavity. This is particularly noteworthy because traditional models of membrane protein formation emphasize the exclusion of lipids, not their trapping. OMPs are essential for a variety of bacterial functions, including signaling, host cell adhesion, catalyzing vital reactions, and facilitating the transport of solutes and nutrients. Understanding the natural variability and novel functions of OMPs like PopA could lead to advancements in antibacterial strategies and synthetic biology, potentially offering new tools to combat bacterial infections and develop innovative medical treatments.