J. Biol. Chem., Vol. 261, Issue 24, 11038-11044, Aug, 1986
The effects of metal ions and temperature on the interaction of cobra venom factor and human complement factor B
P Hensley, MC O'Keefe, CJ Spangler, JC Osborne Jr and CW Vogel
An alternative pathway C3 convertase is formed by the equilibrium
association of Factor B with cobra venom factor (CVF) followed by the
activation step catalyzed by Factor D. However, the association of Factor B
with CVF has only occasionally been demonstrated and has not been
quantitatively analyzed. Here we show that in the absence of metals the two
proteins have significant affinity for each other and reversibly associate
in a one-to-one stoichiometry with a dissociation constant of 11.6 microM.
Upon the addition of metal ions, the complex is stabilized only 2- to
30-fold in the order Ni2+(Kd = 6.6 microM) less than Mg2+(Kd = 1.1 microM)
less than Mn2+(Kd = 0.4 microM). These results suggest that metal ions may
be less important in stabilizing the CVF.B complex and more important in
promoting the subsequent equilibrium association of CVF.B with Factor D.
The stability of the CVF.B complex is variously dependent on temperature in
the range studied (14-21 degrees C) depending on the metal ion that is
present. The complex formation was demonstrated in the analytical
ultracentrifuge at sedimentation equilibrium employing a combination of
single- and multiple-independent variable nonlinear least squares
analytical techniques. Two different numerical approaches gave very similar
results.