[Chimera-users] Morphing, ligands, and secondary structure

[Yan Kung]

Hi Chimera,

I’m a new-ish user, and I’ve found that morphing structures is usually very straightforward and easy to use. But I’m now running into an issue with morphing and ligands (and secondary structure).

I’d like to make a single morph composed of states A-B-C-B-A (so 4 movements between 5 states). These movements are: (1) A-B: domain opens, (2) B-C: a ligand flies out, (3) C-B: the same ligand flies back in, and (4) B-A: domain closes. First problem: the ligand does not appear in the resulting morph, a problem suggested by the documentation, which I have tried (and failed) to solve using the tips I found in archived posts from this mailing list. Also, because the ligand has to fly in and out, I can’t simply superimpose the ligand from any of the individual states over the morph.

So I tried a workaround: make each movement a separate morph. This works for movements 2 and 3 (where the ligand flies out and in). But the ligand still does not appear in movements 1 and 4 (where the ligand remains in place and the domain moves). I’m not sure why the ligand’s appearance would depend on whether it flies in/out, or whether a domain moves… But it seems to.

Moreover, a second problem emerges that has to do with secondary structure and is difficult to explain. (Essentially: a few protein regions are on the border between helices and loops such that they appear as helices in some states but as loops in others, and vice versa. If possible, I’d like the secondary structure to remain constant across all states, or else it’s distracting. Even still, I’ve tried to embrace this and use ksdssp to show the helices/loop switching back and forth, but this is distracting as they flicker between helices and loops, each region at its own separate frame. Specifying ksdssp only in certain frames to minimize the flickering doesn’t work either, as different regions switch back and forth at different times.) The only solution I can think of that would maintain the same secondary structure throughout is to just make a single morph of all movements (and not use ksdssp). But this puts me back where I started!

Any ideas?

(Separately, I realize that I could make a simpler morph of just A-B-C, then record it as “roundtrip”, i.e. forward and backwards, to achieve the same thing as A-B-C-B-A. But this doesn’t solve the problems above.)

Thanks very much,
Yan

--
Yan Kung
Assistant Professor
Department of Chemistry
Bryn Mawr College
http://www.brynmawr.edu/people/yan-kung
Follow: @KungLab<https://twitter.com/KungLab>
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