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. 1999 Oct;181(19):6103–6107. doi: 10.1128/jb.181.19.6103-6107.1999

TABLE 1.

Mutations in helix α4 and their effects on toxin stability and toxicity

Mutation Trypsin stabilitya Toxicityb BBMV protein bindingc
Q133R Stable Nontoxic +
I132S Stable Nontoxic +
I132L Stable Nontoxic +
I132V Stable Nontoxic +
I132N Stable Nontoxic +
R131L Stable Reduced +
R131C Stable No change NT
R131S Stable No change NT
M130I Stable No change NT
M137T Stable No change NT
F134L Stable Enhancedd NT
Q133H Stable No change NT
I132V-D136Y Stable Reduced NT
M130I-R131L Unstable
I132F-N135S Unstable
F134A-M137I Unstable
a

As demonstrated in Fig. 1. 

b

LC50 were determined with infected E. coli cells as described in Materials and Methods. Nontoxic means no toxicity was evident with the most concentrated suspension of either M13-infected cells or of E. coli clones (undiluted cells at 2 × 108 to 3 × 108 ml−1). No change means that the LC50 was within the same range as that of cells infected with the wild type. Reduced means that there was a >10-fold increase in the LC50. 

c

As shown in Fig. 2. NT, not tested; +, protein binding evident. 

d

The LC50 was 106 cells (6.6 × 105 to 1.3 × 106 for 95% confidence limits) for the F134L mutant versus 1.9 × 106 (1.3 × 106 to 3.3 × 106 for 95% confidence limits) for the wild-type infected cells.