Histidine-21 is involved in diphtheria toxin NAD+ binding.
Histidine-21 is the sole histidine present in the A chain of diphtheria toxin and recent evidence suggests that it is involved in NAD+ binding. Fluorimetric assays of NAD+ binding and diethylpyrocarbonate modification performed at different pH values provide further insights on the role of this residue and indicate that its pKa value is 6.3. Conformational changes of subunit A of diphtheria toxin have been detected by analysis of tryptophan fluorescence in the pH 2.5-4 and pH 9-10.5 ranges. This indicates that histidine-21 is unlikely to be involved in the low pH-driven conformational change of diphtheria toxin.
Centro C.N.R. Biomembrane e Dipartimento di Scienze Biomediche, Università di Padova, Italy.
E
E
Papini
G
G
Schiavo
R
R
Rappuoli
C
C
Montecucco
D001665:Binding Sites; D004167:Diphtheria Toxin / Q000378:metabolism*; D006639:Histidine / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D009243:NAD / Q000378:metabolism*; D011487:Protein Conformation
D004167:Diphtheria Toxin; D009243:NAD; D006639:Histidine