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Contributions of the S100A9 C‑Terminal Tail to High-Affinity Mn(II) Chelation by the Host-Defense Protein Human Calprotectin
journal contribution
posted on 2013-11-27, 00:00 authored by Megan Brunjes Brophy, Toshiki G. Nakashige, Aleth Gaillard, Elizabeth M. NolanHuman
calprotectin (CP) is an antimicrobial protein that coordinates
Mn(II) with high affinity in a Ca(II)-dependent manner at an unusual
histidine-rich site (site 2) formed at the S100A8/S100A9 dimer interface.
We present a 16-member CP mutant family where mutations in the S100A9
C-terminal tail (residues 96–114) are employed to evaluate
the contributions of this region, which houses three histidines and
four acidic residues, to Mn(II) coordination at site 2. The results
from analytical size-exclusion chromatography, Mn(II) competition
titrations, and electron paramagnetic resonance spectroscopy establish
that the C-terminal tail is essential for high-affinity Mn(II) coordination
by CP in solution. The studies indicate that His103 and His105 (HXH
motif) of the tail complete the Mn(II) coordination sphere in solution,
affording an unprecedented biological His6 site. These
solution studies are in agreement with a Mn(II)-CP crystal structure
reported recently (Damo, S. M.; et al. Proc. Natl. Acad. Sci.
U.S.A. 2013, 110, 3841). Remarkably
high-affinity Mn(II) binding is retained when either H103 or H105
are mutated to Ala, when the HXH motif is shifted from positions 103–105
to 104–106, and when the human tail is substituted by the C-terminal
tail of murine S100A9. Nevertheless, antibacterial activity assays
employing human CP mutants reveal that the native disposition of His
residues is important for conferring growth inhibition against Escherichia coli and Staphylococcus aureus. Within the S100 family, the S100A8/S100A9 heterooligomer is essential
for providing high-affinity Mn(II) binding; the S100A7, S100A9(C3S),
S100A12, and S100B homodimers do not exhibit such Mn(II)-binding capacity.