1606: Cryo-EM Freestyle & Density 2
Closed since over 7 years ago
Overall Prediction Electron DensitySummary
- Created
- December 04, 2018
- Expires
- Max points
- 100
This protein is another part of the same protein complex with multiple subunits from Puzzle 1554, Puzzle 1588, and Puzzle 1598 which has been the target of cryo-EM experiments. Like in Puzzle 1598, we are giving you 2 weeks and an extended chain to start with, so good luck!
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Bruno Kestemont Lv 1
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Susume Lv 1
I am used to the idea that long blue sidechains flop around in solution and may not show up well in the cloud, but in 1606 there seems to be an orange tyrosine that has two preferred positions, both of which appear clearly in the cloud. 112 TYR has a primary pocket for the sidechain that points toward the sidechain of 91 LYS. If the ED threshold is high, this is the only pocket visible. But if you lower the threshold a bit, a secondary pocket becomes visible, about 90 degrees off from the first, pointing toward the sidechain of 89 LEU. This pocket, like the other one, even has a tip for the tip of the TYR to fit into. I have one track where 112 TYR has settled into the primary pocket (density score 35.4, segment score 49.3), and another track where it has settled into the secondary pocket (density score 28.4, segment score 58.0). One of my teammates also reports a high-scoring TYR 112 that has settled in the less visible pocket.
Is it realistic that a tyrosine would have two clear preferred positions, or do you think this is just an artifact in the cloud?
Susume Lv 1
In NMR (as opposed to crystallography) it seems common to take the average among an ensemble of conformations and call that the solution. In this case, since the two positions for the tyrosine are visibly discrete, one might argue that two overall conformations, one with 112 tyr in position A and the other in position B, would constitute an objectively better solution to the ED map than the average between them.
This begs the question of whether one could propose an ensemble of conformations as the best solution to an ED map, rather than a single conformation. Would the measures typically used to assess the goodness of a solution still make sense? Would protein scientists accept such an ensemble as a valid solution?
beta_helix Staff Lv 1
That is indeed interesting!
It’s a bit hard to visualize it without seeing pictures, but this sounds like a fairly typical case of alternate conformations.
While this is pretty common in crystal structures of reasonably high resolution, typically cryo-EM maps aren’t high enough resolution to see them… but it wouldn't be surprising if some of the more recently solved ones are high enough resolution to find them (on rare occasions).
Susume Lv 1
beta_helix Staff Lv 1
Bruno Kestemont Lv 1
1606 TYR 112 Pocket #1
1606 TYR 112 Pocket #2