Table 1 Characteristics of CDTa-specific and CDTb-specific families of nanobodies

From: Selection of Nanobodies that Block the Enzymatic and Cytotoxic Activities of the Binary Clostridium Difficile Toxin CDT

specificity

llama

family

isolates

variants

CDR3

affinity (Kd)

epitope

IC50 tox

IC50 ART

CDTa

6

l+8

2

1

ECGGYGAH

1 nM

1

2 nM

2 nM

 

6

l-14

2

1

TYRPNTFTPAEYDY

1.5 nM

2

> 1 µM

4 nM

 

6

l-15

4

2

GGFTEAYSGTYYPDS

1.5 nM

3

> 1 µM

4 nM

 

6

l+18

8

5

GGSGYGCYAFTPAYGMDY

1.5 nM

2,3

50 nM

4 nM

 

5037

s-21

18

4

ADQRVGYIEYYSGSSGKEYDY

3 nM

2,3

50 nM

4 nM

CDTb

180

l-3

13

9

RGY

> 50 nM

1

> 1 µM

-

 

180

l-15.1

13

10

KVGANILTRSIGYKY

0.5 nM

1

4 nM

-

 

180

l-15.3

1

1

TNKBYTDGRLEEYDY

9 nM

2

> 1 µM

-

 

180

l-19

1

1

DGRSNLRANYDSADYGMAY

15 nM

3

> 1 µM

-

  1. Family names indicate the presence of a short (s) or long hinge (l), the absence (-) or presence (+) of a disulfide bond connecting CDR2 and CDR3 and the length of the CDR3 in numbers of amino acid residues. Isolates indicates the number of clones selected per family, variants indicates the number of clones carrying distinct but evidently related amino acid sequences. Variant amino acid positions in the CDR3 are indicated in red. Epitopes are numbered arbitrarily (nanobodies that block the binding of one another are considered to recognize the same or overlapping epitopes). “IC50 tox” indicates the nanobody concentration required to inhibit 50% rounding of HT29 cells upon incubation with 2 nM CDTa+b for 4 h at 37°C. “IC50 ART” indicates the nanobody concentration required to inhibit ADP-ribosylation of actin by 2 nM CDTa by 50%.