PDB file 1DBO

This file depicts a complex of G-Actin with the C-terminal half of gelsolin, with bound ATP & Ca++The structure was solved by R. C. Robinson, M. Mejillano, V. P. Le, L. D. Burtnick, H. L. Yin, & S. Choe  in 1999.

Suggested display options:

Color the protein chain and display as cartoon.
Select hetero-ligand, display as spacefill, and color CPK.
There are two Ca++ binding sites, plus Ca++ is substituting for Mg++ at the nucleotide-binding site of actin. 

What is the secondary structure at each Ca++ binding site?

Residues of one Ca++ binding site may be selected as glu167a, asp487b, gly492b, pro494b (Chain a is actin; chain b is gelsolin.) Display as ball & stick and color CPK.
What atoms of gelsolin and actin interact with Ca++?

What subdomains of actin are bound by gelsolin?
How is this consistent with the role of gelsolin?
What type of residues provide ligands to the other Ca++ in gelsolin?
How do the Ca++ binding sites compare to those in calmodulin

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