. Author manuscript; available in PMC: 2016 Mar 4.

Published in final edited form as: J Am Chem Soc. 2015 Feb 18;137(8):3004–3016. doi: 10.1021/ja512204s

Table 1.

Previously reported Ca(II)-coordination by S100A8 and S100A9 in CP^a

EF-hand	Ca(II)-coordinating groups	Coordination number	Net charge
A8, N-terminal Non-canonical	Ser20 (C=O)^b, Lys23 (C=O), Asn25 (C=O), Ala28 (C=O), H₂O	5	0
A8, C-terminal Canonical	Asp59 (Oδ), Asn61 (Oδ), Asp63 (Oδ1), Ala65 (C=O) Glu70 (Oε1 and Oε2), H₂O	7	−4
A9, N-terminal Non-canonical	Ser23 (C=O), Leu26 (C=O), His28 (C=O), Thr31 (C=O), Glu36 (Oε1), H₂O	6	−1
A9, C-terminal Canonical	Asp67 (Oδ), Asn69 (Oδ), Asp71 (Oδ1), Gln73 (C=O), Glu78 (Oε1 and Oε2), H₂O	7	−4

Taken from the crystal structure of the Ca(II)-bound CP-Ser heterotetramer (PDB 1XK4, reference ¹⁸).

C=O indicates coordination by the carbonyl oxygen of the peptide backbone. In the 1XK4 structure, the Ca(II) ions are modeled at 100% occupancy in the canonical C-terminal EF-hand sites, and the Ca(II) ions in the non-canonical N-terminal EF-hand sites are modeled at 70% occupancy.