These movies are based on the following structures. Feel free to download the movies and to use them in public, but please use them unadulterated (including the reference to the moviemakers) as they took us much time and effort. Also please reference the appropriate authors.

Choe, H., L Burtnick, L. D., Mejillano, M., Yin, H. L., Robinson, R. C. & Choe, S. (2002). The calcium activation of gelsolin: Insights from the 3 Å structure of the G4-G6/actin complex. JMB in press.

Robinson, R. C., Mejillano, M., Le, V. P., Burtnick, L. D., Yin, H. L. & Choe, S. (1999). Domain movement in gelsolin: A calcium-activated switch. Science 286, 1939-1942.

Burtnick, L. D., Koepf, E. K., Grimes, J. M., Jones, E.Y., Stuart, D. I., McLaughlin, P. J. & Robinson, R. C. (1997). The crystal structure of plasma gelsolin: Implications for actin severing, capping and nucleation. Cell 90, 661-670.

McLaughlin, P., Gooch, J. T., Mannherz, M.-G. & Weeds, A. G. (1993). Structure of gelsolin segment 1-actin complex and the mechanism of severing. Nature 364, 685-692.

Kazmirski, S. L., Isaacson, R. L., An, C., Buckle, A., Johnson, C. M., Daggett, V. & Fersht, A. R. (2002). Loss of a metal-binding site in gelsolin leads to familial amyloidosis - Finnish type. Nat. Struct. Biol. 9, 112-116.


The calcium-free form of gelsolin (g123456_W.mov)
Here is a rotation of the inactive form of gelsolin. In this conformation gelsolin cannot bind to actin. The two actin-capping sites (on G1 and G4) and its filament side-binding site on G2 are obscured by G3, G6 and the C-terminal tail, respectively. We call these the G1-G3, G4-G6, and the tail latches. Standard colours are used for the domains: G1 red, G2 light green, G3 yellow, G4 pink, G5 dark green and G6 orange.

The calcium/actin-bound form of G4-G6 (g456ca_W.mov)
Here is a rotation of gelsolin domains 4, 5 and 6 bound to both calcium and actin. Actin is shown in cyan and the 4 calcium sites fall into two classes. Type 1 (gold, 1) is sandwiched between G4 and actin, and Type 2 (grey, 3) are coordinated entirely by gelsolin.

The overall activation of G4-G6 (g456_W.mov)
Here we have morphed back and forth between the G4-G6 in the first two movies. See how the sheet between G4 (pink) and G6 (orange) is severed during activation to allow G6 to make a new interface with G5 (green). This is the G4-G6 latch. Please see the next movie to see why such large changes are needed.

The significance of these domain movements in G4-G6 (g456act_W.mov)
Here we show actin (cyan) coming in to dock at its binding site on activated G4-G6. G6 has to move a great distance (last movie) to allow actin into this site.

The position of the calcium-binding sites on the calcium-free form of gelsolin (g123456ca_W.mov)
Here is the same rotation of the inactive form of gelsolin as in the first movie, but with all the calcium ions shown at their future binding sites. Several of these calcium ions appear to be ideally positioned to spring open the G1-G3, G4-G6 and the tail latches to enable gelsolin to bind to actin. The following movies show the detailed activations of individual gelsolin domains on binding calcium, and we suggest what they may mean for activation of whole gelsolin.

Calcium activation of gelsolin domain 1 (g1_W.mov)
Here we have morphed from the calcium-free G1 to Paul McLaughlin’s calcium & actin bound G1, and back again. The only large changes seen are in the green portion, which is the N-terminus of G2. See the significance of this in the next movie.

The significance of the calcium binding to gelsolin domain 1 (g1_2_W.mov)
This is the same setup as in the previous movie but we also have depicted actin in grey (the calcium is now in gold). On G1 (red) binding calcium, the green portion moves against actin, and points towards what would be the next actin in a filament, the actin to which G2 is thought to bind (not shown). Hence this calcium seems to be important in repositioning G1 and G2 relative to each other so they can interact simultaneously with two longitudinal actins in a filament.

Calcium activation of gelsolin domain 2 (g2_W.mov)
Here we have morphed from the calcium-free G2 into Alan Fersht’s cadmium-activated G2 (note that there’s no actin bound here), and back again. There are changes in the terminus and the A-B loop. The reorientation of residue Asp-259 to coordinate the incoming calcium may help to alter the geometry between G2 and G3, as this residue lies in the G2-G3 loop. However, we think this is a minor role of this calcium. Please see the next movie for why this may be the case.

Calcium activation of gelsolin domain 2 relative to the C-terminal tail (g2tail2_W.mov)
Here we’ve added the C-terminal tail from calcium-free gelsolin (orange) to the previous movie. The tail-latch mechanism has this orange helix dissociating from G2 (green) to reveal the F-actin binding site on G2. There seems to be little effect of activation on G2 around the C-terminal tail contact site. So, we can’t attribute opening of the tail latch directly to binding this calcium. There is a major change, however, in the A-B loop. See how Arg-168 and Arg-169 move (note that not all the atoms are shown in these residues). This change may be the key for activation of whole gelsolin. Please see the next movie for details.

Calcium activation of gelsolin domain 2 relative to G6 (g2g6_W.mov)
Here we’ve incorporated the C-terminal tail and G6 from calcium-free gelsolin (orange) into the movie. See how the A-B loop of G2 moves away from G6 on calcium binding. Calcium binding to G2 may be weakening the interaction between G2 and G6, hence contributing to the opening of the tail latch.

Calcium activation of gelsolin domain 4 (g4_W.mov)
Here we have morphed from the calcium-free G4 to the calcium & actin-bound G4, and back again. The major changes seen are in the green portion, which is the N-terminus of G5. Here, Arg-526 leaves the calcium-binding site to allow the calcium in. See the significance of this in the next movie.

The significance of calcium binding to gelsolin domain 4 (g4g5_W.mov)
This is the same setup as in the previous movie but we have included the whole of G5 (dark green). The movement of Arg-526 appears to drag the whole of G5 with it. Hence calcium binding in G4 seems to be important for positioning G4 and G5 relative to each other in the active conformation.

Calcium activation of gelsolin domain 5 (g5__W.mov)
Here we have morphed from the calcium-free G5 to the calcium & actin-bound G5, and back again. There are major changes in the A’-A loop, which was seen in the last two movies to be due to calcium binding to G4. But the biggest change is the expulsion of Arg-629 from the calcium-binding site to allow in the G5 calcium. See the significance of this in the next movie.

The significance of calcium binding to gelsolin domain 5 (g56_W.mov)
This is the same setup as in the previous movie but we have included G6 (orange). The movement of Arg-629 appears to unmask a binding site on G5 for G6. The G6 binding residues on G5 are shown in orange, and the scarlet residue binds both calcium and G6. Calcium binding in G5 causes conformational changes that reveal and order a binding site between G5 and G6.

Calcium activation of gelsolin domain 6 (g6_W.mov)
Here we have morphed from the calcium-free G6 to the calcium & actin-bound G6, and back again. There are a number of changes going on - straightening of the helix and ordering of the A-B loop - and we’ll focus on these in the next few movies.

Significance of calcium binding in gelsolin domain 6: part 1(g6g4_W.mov)
This is the same setup as in the previous movie but we have included the calcium-free positioning of G4 (pink). The straightening of the G6 helix appears to pull G6 away from G4. This is the G4-G6 latch. Calcium binding to G6 may help to induce this change.

Significance of calcium binding in gelsolin domain 6: part 2 (g6act_W.mov)
This is the same setup as in the previous movie but we have included a portion of actin (cyan) in the position at which it ends up bound to G6 in the activated form of gelsolin. Calcium binding reorders the actin-binding residues in G6 to allow it to bind to actin.

Significance of calcium binding in gelsolin domain 6: part 3 (g2g6_3_W.mov)
This movie shows the activation of G6, as seen in the last 3 movies, in relation to calcium-free G2 (green). Asp-670 at the start is bound to Arg-168 and Arg-169 in G2 and finishes up coordinating the calcium. So calcium binding to G6 will weaken the G2-G6 interaction and help spring the tail latch. This may be cooperative with the G2 activation. See the final movie for details.

Cooperativity between calcium activation of G2 and G6 (g2g6_2_W.mov)
This movie shows the activation of G2 and G6 simultaneously. The two domains have been positioned as they are in the calcium-free structure. Calcium binding to G2 moves Arg-168 and Arg-169 away from Asp-670. Similarly, calcium binding to G6 moves Asp-670 away from Arg-168 and Arg-169 in G2. Therefore, cooperative activation of both of these domains may spring the tail latch, thus activating the whole molecule.

To the top