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Cys
S
S
S
Cys
S
Zn
Zn
His
His
His
N
N
N
N
NH
N
Zn
Cu
Zn
Zn
Glu
Glu
Glu
O
Zn
O
O
Zn
O
Zn
Zn
O
O
O
(b)
Glu
117
O
N
Thr
199
O
O
His
119
N
H
H
O
Glu
106
O
Zn
NH
2
N
N
NH
O
Asn
244
O
HN
Gln
92
NH
Trp
97
His
94
His
95
Met
247
O
HN
NH
Figure 2.5.
(a) Zinc−ligand interactions. With few exceptions, zinc ligands in proteins
are cysteine (Cys) (S-donor), histidine (His) (N-donor), or glutamate (Glu)/aspartate
(Asp) (O-donor). For cysteine, there is a single mode of interaction. For histidine,
binding occurs with either one of the two nitrogen atoms of the imidazole ring. For
glutamate/aspartate, binding modes include one oxygen, which can be syn or anti (not
shown), or both oxygens of the carboxylate. All three ligands can bridge one or several
zinc ions. For cysteine, there are one, two, or three bridges. For histidine, the only
bridges known are those between zinc and copper in superoxide dismutase (SOD1)
and between zinc and zinc in the zinc transporter CzrB (
Thermus thermophilus
).
Aspartate/glutamate can form a bridge with the two oxygens of the carboxylate. (b)
Zinc binding to amino acids (adapted from Maret and Li [75] with the permission of
the American Chemical Society).
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