intra base pair and inter base pair step parameters

[deligkaris]

dear 3dna community,

If I have the AT intra base pair parameters (shear, stretch, stagger, etc), will these parameters be exactly the same for a TA base pair, or will they have the opposite sign? (the absolute values will be the same but I am not sure about the sign).

Similarly, if I have the AA base pair step parameters (shift, slide, rise etc) will these parameters be exactly the same for a TT base pair step, or will their values have the opposite sign?

Thank you,

[xiangjun]

Thanks for posting your questions on the 3DNA Forum.

The specific points you raised have been mentioned in the initial 2003 3DNA NAR paper, and more recently in the 2015 DSSR NAR paper).

If I have the AT intra base pair parameters (shear, stretch, stagger, etc), will these parameters be exactly the same for a TA base pair, or will they have the opposite sign? (the absolute values will be the same but I am not sure about the sign).

See the section titled "Base pair parameters" in the 2003 3DNA NAR paper.

"To calculate the six complementary base pair parameters of an M–N pair (Shear, Stretch, Stagger, Buckle, Propeller and Opening), where the two z‐axes run in opposite directions, the reference frame of the complementary base N is rotated about the x2‐axis by 180°, i.e. reversing the y2‐ and z2‐axes in Figure 2a. Under this convention, if the base pair is reckoned as an N–M pair, rather than an M–N pair, the x‐axis parameters (Shear and Buckle) reverse their signs. For an M+N pair, e.g. the Hoogsteen A+U in Figure 2b, the x2‐, y2‐ and z2‐axes do not change sign; thus all six parameters for an N+M pair are of opposite sign from those for an M+N pair."

Similarly, if I have the AA base pair step parameters (shift, slide, rise etc) will these parameters be exactly the same for a TT base pair step, or will their values have the opposite sign?

Similar to above. Shift/Tilt change signs while the other four parameters remain the same.

You could easily verify the results yourself by analyzing a DNA duplex (e.g., 355d) by swapping its two strands in the input PDB file. It helps if you do this exercise and post back your findings.

HTH,

Xiang-Jun

[deligkaris]

Thank you.

The parameters that change sign are: shear, buckle, shift, tilt.

I switched helices in 355D. Here is the comparison:

  1   12 # base-pairs ORIGINAL
  2    0 # ***local base-pair & step parameters***
  3 #        Shear    Stretch   Stagger   Buckle   Prop-Tw   Opening     Shift     Slide     Rise      Tilt      Roll      Twist
  4 C-G      0.276    -0.140     0.073     6.930   -17.308    -0.606     0.000     0.000     0.000     0.000     0.000     0.000
  5 G-C     -0.236    -0.182     0.491     9.341   -14.302    -2.077     0.087     0.039     3.200    -3.216     8.520    32.731
  6 C-G      0.244    -0.171     0.159    -4.433    -5.405     0.434     0.496     0.668     3.691     2.847    -9.055    43.879
  7 G-C     -0.255    -0.115     0.008    10.806    -9.449     1.012    -0.138     0.593     3.000     0.967    11.300    25.114
  8 A-T     -0.037    -0.107     0.011     4.724   -15.314     1.601    -0.453    -0.139     3.388    -1.585     1.373    37.500
  9 A-T      0.051    -0.050     0.065     0.442   -15.001     6.233     0.171    -0.325     3.298    -0.330     0.459    37.520
 10 T-A     -0.037    -0.117     0.173    -0.264   -16.744     3.928    -0.011    -0.601     3.219    -0.311    -2.675    32.403
 11 T-A     -0.108    -0.120    -0.004    -1.561   -16.364     5.120    -0.082    -0.397     3.216     1.681    -0.974    33.744
 12 C-G      0.209    -0.127     0.003   -12.410   -10.274    -1.223    -0.267    -0.226     3.465     0.684    -1.686    42.136
 13 G-C     -0.106    -0.053     0.239     4.205    -9.603     3.206     0.700     0.776     3.068    -3.656     4.180    26.581
 14 C-G      0.156    -0.130     0.208     0.283   -17.417    -1.755    -1.311     0.360     3.371    -2.853    -9.368    41.601
 15 G-C     -0.244    -0.069     0.254     4.671    -4.954    -1.620    -0.309     0.211     3.174    -0.679     6.692    33.310
 16
 17
 18
 19
 20
 21
 22
 23
 24   12 # base-pairs SWITCHED
 25    0 # ***local base-pair & step parameters***
 26 #        Shear    Stretch   Stagger   Buckle   Prop-Tw   Opening     Shift     Slide     Rise      Tilt      Roll      Twist
 27 C-G      0.244    -0.069     0.254    -4.671    -4.954    -1.620     0.000     0.000     0.000     0.000     0.000     0.000
 28 G-C     -0.156    -0.130     0.208    -0.283   -17.417    -1.755     0.309     0.211     3.174     0.679     6.692    33.310
 29 C-G      0.106    -0.053     0.239    -4.205    -9.603     3.206     1.311     0.360     3.371     2.853    -9.368    41.601
 30 G-C     -0.209    -0.127     0.003    12.410   -10.274    -1.223    -0.700     0.776     3.068     3.656     4.180    26.581
 31 A-T      0.108    -0.120    -0.004     1.561   -16.364     5.120     0.267    -0.226     3.465    -0.684    -1.686    42.136
 32 A-T      0.037    -0.117     0.173     0.264   -16.744     3.928     0.082    -0.397     3.216    -1.681    -0.974    33.744
 33 T-A     -0.051    -0.050     0.065    -0.442   -15.001     6.233     0.011    -0.601     3.219     0.311    -2.675    32.403
 34 T-A      0.037    -0.107     0.011    -4.724   -15.314     1.601    -0.171    -0.325     3.298     0.330     0.459    37.520
 35 C-G      0.255    -0.115     0.008   -10.806    -9.449     1.012     0.453    -0.139     3.388     1.585     1.373    37.500
 36 G-C     -0.244    -0.171     0.159     4.433    -5.405     0.434     0.138     0.593     3.000    -0.967    11.300    25.114
 37 C-G      0.236    -0.182     0.491    -9.341   -14.302    -2.077    -0.496     0.668     3.691    -2.847    -9.055    43.879
 38 G-C     -0.276    -0.140     0.073    -6.930   -17.308    -0.606    -0.087     0.039     3.200     3.216     8.520    32.731

Thank you Xiang-Jun.

[xiangjun]

Thanks for posting back your worked example on 355d regarding signs of 3DNA-derived base-pair parameters. Just for the record, I wrote a blogpost titled "Effect of reversing strands of a DNA duplex on 3DNA calculated parameters" dated 2012-08-02.

Best regards,

Xiang-Jun