The table below shows the standard main-chain bond lengths derived from small-molecule data by Engh & Huber (1991), with standard deviations in the rightmost column. The atom-labelling follows that used in the X-PLOR dictionary, with additional types, defined by Engh & Huber, asterisked.
Engh R A & Huber R (1991). Accurate bond and angle parameters for X-ray protein structure refinement. Acta Cryst., A47, 392-400.
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Bond | X-PLOR labelling | Value | sigma
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C-N | C-NH1 (except Pro) | 1.329 | 0.014
| C-N (Pro) | 1.341 | 0.016
| | |
C-O | C-O | 1.231 | 0.020
| | |
Calpha-C | CH1E-C (except Gly) | 1.525 | 0.021
| CH2G*-C (Gly) | 1.516 | 0.018
| | |
Calpha-Cbeta | CH1E-CH3E (Ala) | 1.521 | 0.033
| CH1E-CH1E (Ile,Thr,Val) | 1.540 | 0.027
| CH1E-CH2E (the rest) | 1.530 | 0.020
| | |
N-Calpha | NH1-CH1E (except Gly,Pro) | 1.458 | 0.019
| NH1-CH2G* (Gly) | 1.451 | 0.016
| N-CH1E (Pro) | 1.466 | 0.015
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