Table 3. Coordination of the two Mg²⁺ ions.

Bridging atoms are highlighted in bold. Mean distances from structures in the PDB at near-atomic resolution are 2.09 Å for Mg²⁺—OH₂, 2.10 Å for Mg²⁺—O Thr, 2.08 Å for monodentate Mg²⁺—⁻OOC Asp/Glu and 2.5 Å as the maximal accepted distance of bidentate Mg²⁺—⁻OOC Asp/Glu (Harding, 2001 ▶, 2006 ▶). The two coordinating atoms of the Mg-II ion that differ by more than 50% from the mean distance are indicated in italics. Values for the deviation of the mean distance assuming a bidentate coordinating nature are given in parentheses.

Coordinating atom	Distance (Å)	Deviation from mean distance (%)
Mg-I
Thr60 OG1	2.32	+10.5
Asp61 OD1	2.03	−2.4
Asp62 OD2	1.93	−7.2
Asp300 OD2	2.01	−3.4 (19.6)
W20	2.10	+0.5
W61	2.02	−3.3
Mg-II
Glu25 OE2	2.26	+8.7
Asp298 OD1	2.17	+4.3 (13.2)
Asp298 OD2	3.42	+64.4 (36.8)
Asp300 OD1	2.20	+5.8 (12.0)
Asp300 OD2	3.16	+51.2 (26.4)
Thr301 OG1	2.32	+10.5
W38	2.27	+8.6
W61	2.23	+6.7