TABLE 2 .
Idiosyncratic phenotypic profiles of the 7 functionally important TonB Cys substitutionsa
| Mutant | Activityb |
% Fe transport (mean ± SEM)c | ||
|---|---|---|---|---|
| Col B | Col Ia | Col M | ||
| ΔtonB | T,T,T | T,T,T | T,T,T | 0 |
| pKP568d (wt) | 9,9,9 | 8,8,8 | 6,6,6 | 100 ± 4 |
| Y163C | T,T,T | 8,8,8 | T,T,T | 58 ± 2 |
| F180C | 7,7,7 | 4,4,4 | 4,4,4 | 48 ± 2 |
| G186C | 7,7,7 | 5,5,5 | T,T,T | 10 ± 1 |
| F202C | 4,4,4 | 8,8,8 | T,T,T | 38 ± 1e |
| W213C | 6,6,6 | 5,5,5 | 3,3,3 | 20 ± 1 |
| Y215C | 8,8,8 | 3,3,3 | 3,3,3 | 35 ± 2 |
| F230C | 7,7,7 | 8,8,8 | 2,2,2 | 38 ± 1 |
a
Spot titer assays were conducted in strain KP1406 (tonB aroB).
b
Numbers indicate the last 5-fold dilution at which sensitivity to the agent (colicin [Col] B, Ia, or M) was apparent in triplicate assays. T indicates tolerance (no sensitivity) to the particular agent tested. The results for three assays are shown.
c
Initial rates of [55Fe]ferrichrome transport were determined in strain KP1344 (tonB).
d
pKP568 carries a gene encoding TonBC18G, which lacks the sole Cys residue in native TonB. wt, wild type.
e
TonB F202A exhibits 95% transport (26).