Based on the electron cloud on this puzzle, there appears to be an amino acid missing between 65 and 67. Could there be a typographical error in the puzzle that makes it incompatible with the electron density map? To make the protein fit the density map, the sequence 61-HLTIDAVFF-69 should be 61-HLTIxxAVFF-70.
https://fold.it/portal/node/2013442#comment-46945 also
asks if puzzle 2191 is missing at least one residue.
Yes, you're right, there is a missing residue in the starting structure! I'll have to dig a bit to figure out how that happened. We may run this Puzzle 2191 again with a corrected starting structure.
https://fold.it/portal/node/2013442#comment-46953 says
similar things and adds that there is a region in the
Electron Density Cloud with "no density to suggest how
the residue is folded". If this is the case, then instead
of giving us a protein that is missing a residue there,
why not give us the entire protein and instead change
the Electron Density Cloud some?
Would replacing the bad region with a constant density
help? Some ideas for the constant density could be zero,
the average density in the cloud, or the maximum density
in the cloud. Zero would work best for generally empty
regions, and large positive values would work best for
tightly-packed interior regions of the protein.
Another idea would be to approximate the overall
Electron Density D as a spherical Gaussian in 3D, like:
D=density=A*exp(-k*((x-xo)^2 + (y-yo)^2 + (z-zo)^2))
where A and k are positive constants, and xo,yo,zo is
the approximate center of the Electron Density Cloud.
With a good enough approximation, one could then
replace the bad region with the density D given by
the formula above.