Thomas Kehl-Fie, Ph.D., a postdoctoral fellow in Skaar's group, used these altered calprotectins to demonstrate that the protein's ability to bind manganese is required for full inhibition of Staphylococcus aureus growth. The investigators also showed that Staph bacteria require manganese for a certain process the bacteria use to protect themselves from reactive oxygen species.
"These altered calprotectin proteins were key to being able to tease apart the importance of the individual metals zinc and manganese to the bacterium as a whole and to metal-dependent processes within the bacteria," Skaar said. "They're really powerful tools."
Skaar explained that calprotectin likely binds two different metals to increase the range of bacteria that it inhibits. The investigators tested the modified calprotectins against a panel of medically important bacterial pathogens.
"Bacteria have different metal needs," Skaar said. "Some bacteria are more sensitive to the zinc-binding properties of calprotectin, and others are more sensitive to the manganese-binding properties."
To fully understand how calprotectin binds manganese, Damo and Chazin with assistance from Gnter Fritz, Ph.D., at the University of Freiburg in Germany produced calprotectin crystals with manganese bound and determined the protein structure. They found that manganese slips into a position where it interacts with six histidine amino acids of calprotectin.
"It's really beautiful; no one's ever seen a protein chelate (bind) manganese like this," Chazin said.
The structure explains why calprotectin is the only S100 family member that binds manganese and has the strongest antimicrobial action, and it may allow researchers to design a calprotectin that only binds manganese (not zinc). Such a tool would be useful for studying why bacteria require m
|Contact: Leigh MacMillan|
Vanderbilt University Medical Center