Table 2. Metal coordination geometries found in RtcB structures.

Species	PDB ID	Chain	Metal	Ligand	Metal coordination geometry
					Position A	Position B
Homo sapiens	7P3B	A, B	Co2+	GMP	Tetrahedral	Octahedral
Pyrococcus horikoshii	4DWQ	A, B	Mn2+	GMP*	Trigonal bipyramidal	−
	4IT0	A	Mn2+	GMP*	Tetrahedral	Trigonal pyramidal
		B	Mn2+	−	Tetrahedral	Tetrahedral
	4ISZ	A	Mn2+	GTPαS	Tetrahedral	Tetrahedral
		B	Mn2+	GTPαS	Trigonal bipyramidal	Tetrahedral
	4DWR	A, B, C	Mn2+	SO42-	Octahedral	Tetrahedral
	4ISJ	A, B	Mn2+	−	Tetrahedral	−

^*Denotes a GMP ligand covalently bound to the His404 of PhRtcB.