TABLE 2 

Idiosyncratic phenotypic profiles of the 7 functionally important TonB Cys substitutionsa

MutantActivityb% Fe transport (mean ± SEM)c
Col BCol IaCol M
ΔtonBT,T,TT,T,TT,T,T0
pKP568d (wt)9,9,98,8,86,6,6100 ± 4
Y163CT,T,T8,8,8T,T,T58 ± 2
F180C7,7,74,4,44,4,448 ± 2
G186C7,7,75,5,5T,T,T10 ± 1
F202C4,4,48,8,8T,T,T38 ± 1e
W213C6,6,65,5,53,3,320 ± 1
Y215C8,8,83,3,33,3,335 ± 2
F230C7,7,78,8,82,2,238 ± 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).