X-Ray Footprinting Solves Mystery of Metal-Breathing Protein
Caroline Ajo-Franklin, a staff scientist in the Biological Nanostructures Facility at Lawrence Berkeley National Laboratory’s (LBNL) Molecular Foundry (one of the Nanoscale Science Research Centers supported by DOE’s Office of Basic Energy Sciences), teamed up with Corie Ralston to use X-ray mass spectrometry footprinting at LBNL’s Advanced Light Source. Ralston, who works in the Molecular Biophysics and Integrated Bioimaging (MBIB) Division, uses the X-ray mass spectrometry footprinting technique to precisely probe proteins and their surroundings at the Advanced Light Source. Ajo-Franklin and Ralston saw that they could use footprinting to answer a long-standing question in microbiology: how do bacterial proteins interact directly with minerals to transfer electrons and allow the microbe to live?
“Understanding what these interactions between proteins and materials look like can help us design them better,” Ajo-Franklin said, “and give us insight on how to connect living cells with devices.”
Surprisingly, “the biggest finding … was that our proteins bind relatively weakly,” Ajo-Franklin noted. “Most proteins that interface with materials bind really tightly,” changing shape as they form the connection. This particular protein does not appear to change shape at all and only interacts with the mineral in a small area, requiring about five times less binding energy, by comparison, than typical proteins that form biominerals. This finding makes a lot of sense, Ajo-Franklin, because this protein’s job “is to transfer electrons to the mineral, so it doesn’t have to be in contact for very long.”