IDENTIFICATION OF THE TRAPPED CALCIUM IN THE GELSOLIN SEGMENT 1-ACTINCOMPLEX - IMPLICATIONS FOR THE ROLE OF CALCIUM IN THE CONTROL OF GELSOLIN ACTIVITY
Ag. Weeds et al., IDENTIFICATION OF THE TRAPPED CALCIUM IN THE GELSOLIN SEGMENT 1-ACTINCOMPLEX - IMPLICATIONS FOR THE ROLE OF CALCIUM IN THE CONTROL OF GELSOLIN ACTIVITY, FEBS letters, 360(3), 1995, pp. 227-230
The X-ray structure of the complex of actin with gelsolin segment 1 re
vealed the presence of two calcium ions, one bound at an intramolecula
r site within segment 1 and the other bridging the segment directly to
actin. Although earlier calcium binding studies at pH 8.0 revealed on
ly a single calcium trapped in the complex (and also in the binary gel
solin-actin complex), it is here shown that two calcium ions are bound
under the conditions of crystallization at physiological pH. Mutation
of acidic residues in either actin or segment 1 involved in ligation
of the intermolecular calcium ion resulted in loss of one of the bound
calcium ions at pH < 7, but not at pH 8. Thus the calcium ion trapped
in the segment 1-actin complex is that located at the intramolecular
site. The implications of this for gelsolin function are discussed.