The already-accepted bio-nm-v04-003 candidate BNP009 reports an i,i+4 Ca-Ca distance of 6.248 angstrom within a real alpha helix of hen egg-white lysozyme (PDB 6LYZ). Using your Ca9-Ca13 measurement on the supplied crambin (PDB 1CRN) helix, calculate the difference between these two independently sourced, unrelated proteins' i,i+4 spacings. Is this difference small enough to treat both as examples of the same underlying regular alpha-helix geometry? What would a much larger difference (for example, several angstrom) have suggested instead?

Coordinates are in angstrom (1 nm = 10 angstrom). XYZ atom rows are one-based after the two header lines. Use the supplied coordinate snapshot without optimization or periodic wrapping. Use S0008: all 46 CA sites of 1CRN chain A, row i = residue A:i. Residues 9 and 13 lie within the deposited helix span (residues 7-19). Compute the Ca9-Ca13 distance for this protein and subtract the already-published BNP009 value, 6.248 angstrom, for lysozyme's Ca27-Ca31 distance. Report the signed difference (crambin minus lysozyme) in angstrom to three decimal places, and answer the qualitative questions in words. Do not recompute or restate BNP009's own derivation; treat it as a given, already-accepted reference number.

46
PDB 1CRN crambin, 46 CA sites, chain A, model 1; angstrom
C 16.967 12.784 4.338
C 13.856 11.469 6.066
C 13.660 10.707 9.787
C 10.646 8.991 11.408
C 9.448 9.034 15.012
C 8.673 5.314 15.279
C 8.912 2.083 13.258
C 5.145 2.209 12.453
C 5.598 5.767 11.082
C 8.496 4.609 8.837
C 6.500 1.584 7.565
C 3.545 3.935 6.751
C 5.929 6.358 5.055
C 7.331 3.607 2.791
C 3.782 2.599 1.742
C 2.890 6.285 1.126
C 5.895 6.489 -1.213
C 4.933 3.431 -3.326
C 2.792 5.376 -5.797
C 5.366 8.191 -6.018
C 3.767 10.609 -3.513
C 6.143 13.513 -2.696
C 8.114 13.103 0.500
C 6.614 16.317 1.913
C 3.074 14.894 1.756
C 4.180 11.549 3.187
C 5.879 13.502 6.026
C 2.691 15.221 7.194
C 0.715 12.045 6.657
C 2.986 9.994 8.950
C 4.769 12.336 11.360
C 8.140 11.694 9.635
C 10.280 14.760 8.823
C 12.552 15.877 6.036
C 15.930 17.454 6.941
C 18.635 18.861 4.738
C 21.452 16.969 6.513
C 22.019 13.242 7.020
C 21.936 12.911 10.809
C 18.504 12.312 12.298
C 17.924 13.421 15.877
C 17.334 10.956 18.691
C 13.564 11.573 18.836
C 13.257 10.745 15.081
C 15.445 7.667 15.246
C 13.512 5.395 12.878


Attachments:
S0008: item-0004-asset-1.xyz