Table 2.
system |
rC-LG(rC-N)
|
rC-Nu(rC-X)a
|
||
---|---|---|---|---|
bond orderb | Å | bond order | Å | |
DT NAD hydrolysis (O)a | 0.02 | 2.65 | 0.03 | 2.46 |
NAMPT NMN PPi (O) | 0.06 | 2.35 | 0.02 | 2.60 |
PT NAD hydrolysis (O) | 0.11 | 2.14 | 0.001 | 3.50 |
PT NAD Giα1 (S) | 0.13 | 2.10 | 0.09 | 2.55 |
PT NAD αi3C20 (S) | 0.15 | 2.06 | 0.12 | 2.47 |
DT NAD eEF-2 (N) | 0.18 | 1.99 | 0.03 | 2.58 |
The nature of the atom nucleophile depends on the system studied. It is an oxygen atom (O) for the NAD hydrolysis catalyzed by both Diphtheria and Pertussis toxins (DT and PT, respectively) or for the pyrophosphorolysis of NMN catalyzed by NAMPT. It is a sulfur atom (S) for the ADP-ribosylation of Giα1 and αi3C20 peptides by PT toxin. Finally, it is a nitrogen atom (N) when the DT toxin ADP-ribosylates eukaryotic elongation factor 2 (eEF-2).
Pauling bond orders are calculated using the relation ni = e(r-ri)/0.3, where r is the bond length of a single bond (i.e. rC-N = 1.48 Å, rC-S = 1.83 Å, rC-O = 1.44 Å) and ri is the interatomic distance between C1′ and the atom of interest (i.e. rC-LG and rC-Nu).