Bacterial Ancestry of a Human Protein

Bacterial membrane protein has similar structure to proteins that remodel cell membranes in humans.

Red, blue, purple, and red schematics of proteins in ring shapes

Comparison of ESCRT-III protein structures with PspA structure.

Benedikt Junglas, Dirk Schneider, Carsten Sachse

Researchers have discovered remarkable similarities between membrane proteins found in single-celled bacteria and in the cells of complex, multicel­lular creatures, such as humans. The unexpected result could lead to new insights into the workings of the proteins in our cells, advance basic biology, and help treat certain diseases. 

In a recent study, a German research team reported on the structure of a membrane protein called phage shock protein A, or PspA. It is a key part of the so-called phage shock protein system, which helps bacteria deal not only with infective viruses, called bacte­riophages, but a broad range of common membrane stressors: heat, toxins, and osmotic stress that occurs when changes in sol­ute concentrations around a cell trigger surges in water across the membrane. 

To determine the structure of PspA in high resolution, the re­searchers used cryo-electron mi­croscopy, a Nobel Prize-winning technique that images frozen biomolecules. “Looking at [the structure of a protein for] the first time is always a moment of awe and inspiration,” said study co-senior author Carsten Sachse, a professor at Heinrich Heine University in Düsseldorf, Ger­many and the Forschungszen­trum Jülich research center. 

While examining PspA, Sachse and colleagues noticed the protein’s apparent structural similarity to another family of proteins—ESCRT-III proteins— that Sachse’s group routinely studies. An essential protein family, ESCRT-III is involved in the repair and the remodeling of cell membranes in all eukary­otes, or multicellular organisms. 

Further examination of PspA showed for the first time how it forms elongated, spiral-shaped tubes whose inner cavities sur­round portions of membranes. While enclosed by PspA, mem­branes can be formed, dissolved, and reshaped, operating in much the same way as ESCRT-III proteins. Dirk Schneider, a professor of biochemistry at Johannes Gutenberg Uni­versity Mainz, Germany and co-senior author of the study, called ESCRT-III a “nice example of a complex eukary­otic mechanism that was in­vented before in bacteria.” 

The study demonstrates that PspA and ESCRT-III proteins, while separated by hundreds of millions of years of evolution in their respective organisms, still share fundamental functions. Further research on PspA—es­pecially in well-studied micro­organisms—could cast new light on human membrane proteins. Sachse and Schneider suggest that research could further our understanding of viral diseases and neurodegenerative diseases, such as Alzheimer’s, where membranes are compromised. (Cell

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