TABLE 5.

The influence of calcium on ligand recognition by CBM60s

Protein	Ligand	Ka × 103
		m−1
vCBM60	Oat-spelt xylan	7.2 ± 0.8
vCBM60 + 10 mm EDTA	Oat-spelt xylan	n.b.a
vCBM60 (apo form)b	Oat-spelt xylan	n.b.
vCBM60 (apo form)c	Oat-spelt xylan	7.5 ± 0.6
vCBM60 (apo form)	Calciumd	212 ± 6.9
CjCBM60A	Oat-spelt xylan	400 ± 40
CjCBM60A + 10 mm EDTA	Oat-spelt xylan	n.b.
CjCBM60A (apo-form)b	Oat-spelt xylan	n.b.
CjCBM60A (apo-form) + 5 mm Ca2+c	Oat-spelt xylan	312 ± 42
CjCBM60A (apo-form)	Calcium	173 ± 18

^a n.b., no binding.

^b CBM60 (apo form): the apo form of the CBM60s were prepared by treatment with Chelex-100 to remove bound divalent metal ion. Titration was performed in 50 mm Na Hepes, pH 8.0, treated with Chelex-100, with 0.5 or 5 mg/ml oat-spelt xylan.

^c CBM60 (apo form): titration of the apo-form of the CBM60s with xylan was carried out in 50 mm Na Hepes, pH 7.5, containing 5 mm CaCl₂.

^d For calcium, the concentration of calcium in the syringe was 0.5–3 mm.