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. 2013 Dec 5;3:91. doi: 10.3389/fcimb.2013.00091

Table 1.

Equilibrium dissociation constants (Kd) reported for solute binding proteins of Mn-specific ATP-binding cassette transporters and for human calprotectin.

Protein Method Kd (Mn), nM Kd (Zn), nM
Spn PsaA SBPa ITC 3.3 (±0.1) 230 (±2)
Tpa TroA SBPb ITC 7.1 (±0.5) 22 (±4)
Ype YfeA SBPc ITC 18 (±6) 6.7 (±1.6)
Ssu TroA SBPd ITC 250 (±20) 430 (±10)
Sau MntC SBPe ITC, competition 3.8 (±1.1) not determined
Calprotectin + Ca(II)f,g chelator comp 190; 21000 <0.01; <0.24
Calprotectin + Ca(II)h ITC 1.3; 3700 1.4; 5.5
a

20 mM NaH2PO4, pH 6.5, 25 °C, 4.5–20 μM PsaA (McDevitt et al., 2011).

b

100 mM sodium acetate, pH 6.5, 20 °C, 40 μM TroA (Desrosiers et al., 2007).

c

100 mM sodium acetate, pH 6.5, 20 °C, 42 μM YfeA (Desrosiers et al., 2010).

d

20 mM sodium acetate, pH 6.5 at 25 °C, 30 or 90 μM TroA (Zheng et al., 2011).

e

50 mM citrate, 150 mM NaCl, 10% glycerol, pH 6.0, 25 °C, 36–43 μM MntC (Gribenko et al., 2013).

f

Mn parameters measured in 75 mM Hepes, 100 mM NaCl, 0.2 mM Ca(II), pH 7.5, 25 °C. Values for metal site 1 (S1; His6) and metal site 2 (S2; His3Asp) are shown as KdMn1, KdMn2, KdZn1, and KdZn2 (Figure 5).

g

Zn parameters measured in 75 mM Hepes, 100 mM NaCl, 1 mM Ca(II), pH 7.5, room temperature.

h

Measured in 20 mM Tris, 100 mM NaCl, 22.5 μM Ca(II), 5 mM β-mercaptoethanol, pH 7.5, 30 °C, 7.5 μM CP (Kehl-Fie et al., 2011). A ΔS1 mutant CP does not bind Mn tightly in contrast to the ΔS2 mutant, revealing the His6 S1 site is the high affinity site for Mn (Damo et al., 2013).