Using two independent i,i+4 Ca-Ca measurements within the supplied helix, Ca27-Ca31 and Ca28-Ca32, calculate both distances and their difference. Does this pair of measurements support treating residues 25-35 as a fairly regular alpha helix, or does it show a large, irregular jump between consecutive turns? What would a much larger difference between these two i,i+4 distances have indicated 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 S0012: all 129 CA sites of 6LYZ chain A, row i = residue A:i. Residues 27, 28, 31 and 32 all lie within the deposited helix span (residues 25-35). Report both i,i+4 distances and their signed difference in angstrom to three decimals, and answer the qualitative questions in words.

129
PDB 6LYZ hen egg-white lysozyme, 129 CA sites, chain A, model 1; angstrom
C 2.445 10.457 9.182
C 2.396 13.826 7.425
C -1.200 15.052 7.311
C -2.797 17.128 4.559
C -3.979 20.606 5.546
C -7.588 19.557 4.979
C -7.298 15.981 6.233
C -6.065 17.161 9.628
C -8.681 19.915 9.821
C -11.227 17.143 9.311
C -9.710 14.962 12.030
C -9.312 17.616 14.723
C -12.968 18.474 14.148
C -14.069 14.856 14.511
C -12.027 14.963 17.717
C -14.018 17.896 19.087
C -11.404 20.640 18.766
C -13.365 23.109 16.641
C -14.080 25.848 19.183
C -12.724 23.927 22.172
C -12.261 26.661 24.776
C -13.140 29.194 22.079
C -10.435 28.571 19.482
C -11.779 28.107 15.961
C -10.673 24.992 14.084
C -8.312 27.181 12.063
C -6.430 28.273 15.179
C -5.505 24.609 15.559
C -4.492 23.682 12.017
C -2.402 26.857 12.026
C -0.578 26.085 15.269
C 0.120 22.587 13.962
C 1.476 23.709 10.595
C 4.120 25.982 12.108
C 4.710 23.725 15.105
C 5.349 20.531 13.150
C 4.540 20.923 9.459
C 1.700 18.438 9.899
C 4.274 15.746 10.644
C 3.383 13.702 13.723
C 6.824 12.104 13.957
C 8.427 15.463 14.730
C 10.622 16.061 17.776
C 12.810 18.940 18.949
C 15.147 19.257 21.932
C 15.139 22.458 23.991
C 18.089 23.781 25.985
C 16.589 22.875 29.352
C 16.855 19.284 28.170
C 13.145 18.685 27.636
C 11.971 17.581 24.194
C 8.885 18.518 22.183
C 6.636 15.841 20.700
C 4.046 15.335 17.966
C 1.911 17.349 15.555
C 1.284 19.842 18.359
C 4.742 19.591 19.921
C 3.805 18.812 23.524
C 6.598 19.187 26.079
C 8.135 16.486 28.270
C 8.935 18.674 31.277
C 5.215 18.747 32.059
C 2.811 16.826 29.828
C 4.418 13.486 28.994
C 7.171 11.074 30.027
C 10.020 10.221 27.666
C 12.121 9.074 30.620
C 15.050 11.459 30.212
C 13.568 14.735 31.414
C 14.000 15.011 35.179
C 11.889 17.797 36.660
C 9.195 15.862 34.820
C 5.530 16.009 35.808
C 3.595 13.783 33.416
C 0.284 15.630 33.645
C -1.035 13.954 30.501
C -0.117 10.529 31.844
C 1.253 9.486 28.457
C 4.713 8.330 27.412
C 5.808 10.997 24.936
C 6.261 8.425 22.176
C 2.489 7.969 22.134
C 2.138 11.547 20.933
C 3.978 10.584 17.749
C 1.743 7.858 16.338
C -0.493 8.474 13.328
C -3.703 8.580 15.349
C -3.676 12.058 16.882
C -6.137 11.073 19.601
C -3.609 11.188 22.439
C -2.271 14.538 21.243
C -5.696 16.168 21.065
C -6.649 14.687 24.429
C -3.491 16.132 25.968
C -3.642 19.372 23.984
C -7.077 19.930 25.515
C -5.564 19.899 29.003
C -2.695 22.188 28.043
C -5.126 24.777 26.684
C -7.754 24.640 29.429
C -5.195 25.028 32.101
C -4.564 28.766 31.850
C -2.659 30.551 29.085
C -4.933 29.247 26.332
C -2.996 28.667 23.113
C -0.252 31.077 24.179
C 1.231 27.860 25.559
C 2.358 27.366 21.961
C 5.094 29.887 21.171
C 4.474 29.226 17.483
C 0.732 29.873 17.670
C 1.321 33.104 19.591
C 3.974 34.485 17.242
C 2.707 33.315 13.854
C -0.977 32.469 14.254
C -2.486 34.814 16.838
C -4.378 37.635 15.138
C -4.023 36.614 11.496
C -7.293 35.432 9.966
C -6.730 31.751 10.726
C -9.825 30.681 8.823
C -7.629 30.645 5.725
C -6.268 27.322 6.975
C -9.607 25.561 6.574
C -10.680 27.053 3.257
C -11.354 24.358 0.661
C -12.328 21.822 3.316
C -15.407 19.600 3.434
C -15.930 20.242 7.145


Attachments:
S0012: item-0005-asset-1.xyz