. 2021 Mar 1;125(9):2251–2257. doi: 10.1021/acs.jpcb.0c11077

Table 6. First- and Second-Shell Residues That Bind to the Metal Ions in MxaF and XoxF^a.

MxaF/Ca²⁺		XoxF/La³⁺
first shell	second shell	first shell	second shell
Glu¹⁷⁷	Trp²⁶⁵	Glu¹⁹⁷	Trp²⁸⁹, w1035, w1062
Asn²⁶¹		Asn²⁸⁵	w1041
Asp³⁰³	Trp²⁶⁵, Arg³³¹	Asp³²⁷	Arg³⁵⁴, w834
		Asp³²⁹	Trp²⁶⁷, Arg³⁵⁴
PQQ	Thr¹⁵⁹, Ser¹⁷⁴	PQQ^b	Gly¹⁹⁶, w1041

Residues that can form hydrogen bonds with the metal-ion ligands are considered as the second shell. “w” stands for water.

Residue Thr²⁶⁵ binds to the distal oxygen of the PQQ carboxylate, which is not directly coordinated to the metal. The charge of the coordination shell and types of ligands both affect the affinity for ions when a native metal cofactor is replaced.^26,27

Table 6. First- and Second-Shell Residues That Bind to the Metal Ions in MxaF and XoxFa.

Table 6. First- and Second-Shell Residues That Bind to the Metal Ions in MxaF and XoxF^a.