XIAP and cIAP1 are members of the inhibitor of apoptosis protein (IAP) family and are key regulators of anti-apoptotic and pro-survival signaling pathways. Overexpression of IAPs occurs in various cancers and has been associated with tumor progression and resistance to treatment.[2]
Table 1. Hydrogen bonds options between backbone atoms in secondary structure.
| # |
Atoms |
Distance (A) |
Angle N-O-C (°) |
| Alfa helix |
| 1 |
N(839THR)- O(820LEU) |
3.54 |
113.57 |
| 2 |
N(839THR)- O(811GLN) |
3.57 |
151.84 |
| 3 |
N(833SER)- O(802GLU) |
2.83 |
160.89 |
| 4 |
N(825LEU)- O(794LEU)) |
2.81 |
163.2 |
| 5 |
N(817LEU)- O(786LEU) |
2.88 |
167.82 |
| 6 |
N(808GLN)- O(776HIS) |
3.06 |
156.32 |
| Beta Sheet |
| 1 |
N(342VAL)- O(412LEU) |
2.97 |
167.62 |
| 2 |
N(409LEU)- O(345VAL) |
2.98 |
150.87 |
| 3 |
N(349LYS)- O(275TYR) |
2.96 |
161.62 |
| 4 |
N(353TYR)- O(272LYS)) |
2.93 |
156.74 |
As can be seen from the data in Table 1, both in α-helices and β-strands bond lengths are close to 3 Å and the angle of N-O-C to 160 °. The higher conservatism of the coupling parameters in α-helices is probably due to the fact that the structural features of α-helical packing make this secondary structure the most stable [3]. In general, the hydrogen bond achieves maximum strength at an angle of N-O-C 180 °, but the mutual influence of other protein atoms and in principle the conformation peculiarities of the α-helix does not allow this angle to take such a value, and it fluctuates around 160 °, as it was said earlier.