Table 3.
Numbers of specific a′-a-a′ combinations in natural antiparallel coiled-coil structures
| Amino acid at a |
a′ = a′ = Ile |
a′ = a′ = Leu |
||||
|---|---|---|---|---|---|---|
| Observed | Expected | Observed/expected | Observed | Expected | Observed/expected | |
| Ile | 6 | 9.4 | 0.6 | 26 | 16.5 | 1.6 |
| Leu | 19 | 14.2 | 1.3 | 21 | 24.7 | 0.9 |
| Sum (all amino acids) | 59 | 103 | ||||
Expected numbers were calculated by using the percentage of occurrence of Ile and Leu at all a sites of coiled-coil structures in the CC+ database with 70% sequence identity or lower. These values are 16% and 24%, respectively. Note: the theoretical DELI(L/I)′ value is equal to −RT(ln(26/6) − ln(21/19)); the ratios of the raw numbers for Ile at both sites or Leu at both sites are self-normalizing, though the same result is obtained by using the normalized values (−RT(ln1.6 − ln 0.9 + ln1.3 − ln 0.6)).