Table 5. Hydrogen-bond and salt-bridge interactions characteristic of Hb quaternary states.
Values in parentheses are for the pseudo-symmetrical contact where there are two αβ dimers in the crystallographic asymmetric unit.
| Residue 1 | Residue 2 | T deoxyHb (2dn2) | T aquometHb (1hgb) | R HbO2 (2dn1) | R aquometHb (3p5q) | R2 HbCO (1bbb) | RR2 HbCO (1mko) | R3 HbCO (1yzi) | ζ2β2 S HbCO (3w4u) | Cat aquometHb (3gqp) | IsdHN2N3–aquometHb (4xs0) |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Hydrogen bonds at the α1β2 interface | |||||||||||
| β2Asp99 OD1/2 | α1Tyr42 OH | 2.5 (2.5) | 2.5 (2.5) | — | — | — | — | — | 2.4 (2.4) | 2.8 (2.5) | 2.5 |
| β2Asp99 OD1/2 | α1Asn97 ND2 | 2.8 (2.8) | 3.9 (3.1) | — | — | — | — | — | 2.9 (2.8) | 2.8 (2.7) | 2.7 |
| α1Asp94 OD1/2 | β2Trp37 NE1 | 2.9 (2.8) | 3.2 (3.1) | 3.7 | 3.7 | 3.8 (3.8) | 3.6 (3.4) | 3.5 | — | — | — |
| α1Asp94 OD1/2 | β2Asn102 ND2 | — | — | 2.8 | 2.8 | 2.7 (2.8) | 2.8 (2.8) | 2.8 | — | — | — |
| β2Trp37 NE1 | β2Asn102 OD1 | — | — | 2.9 | 3.0 | 3.0 (3.0) | 3.1 (3.1) | 3.3 | 3.1 (3.2) | (2.9) | 3.5 |
| C-terminal salt bridges | |||||||||||
| α1Arg141 NH1/2 | α2Asp126 OD2 | 2.8 (2.7) | 2.5 (2.4) | — | Disordered | — | — | — | — | (2.9) | 2.9 |
| α1Arg141 OXT | α2Lys127 NZ | 2.8 (2.8) | 2.6 (2.8) | — | Disordered | — | — | — | — | 2.9 | — |
| β2His146 NE2 | β2Asp94 OD(1) | 2.6 (2.8) | 2.8 (2.6) | — | — | — | — | — | 3.0 (2.6) | 2.9 (3.0) | 3.6 |
| β2His146 OXT | α1Lys40 NZ | 2.8 (2.6) | 2.4 (2.7) | — | — | — | — | — | 2.9 (2.7) | 2.6 (2.5) | 2.7 |