Identification of the trapped calcium in the gelsolin segment 1-actin complex: implications for the role of calcium in the control of gelsolin activity.
The X-ray structure of the complex of actin with gelsolin segment 1 revealed the presence of two calcium ions, one bound at an intramolecular site within segment 1 and the other bridging the segment directly to actin. Although earlier calcium binding studies at pH 8.0 revealed only a single calcium trapped in the complex (and also in the binary gelsolin-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.
Weeds
A G
AG
MRC Laboratory of Molecular Biology, Cambridge, UK.
Gooch
J
J
McLaughlin
P
P
Pope
B
B
Bengtsdotter
M
M
Karlsson
R
R
D000199:Actins / Q000737:chemistry*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002645:Chickens; D018260:Gelsolin / Q000737:chemistry*; D066298:In Vitro Techniques; D009124:Muscle Proteins / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D011817:Rabbits; D013329:Structure-Activity Relationship
D000199:Actins; D018260:Gelsolin; D009124:Muscle Proteins; D002118:Calcium