Role of the N-terminal region of the A chain in beta 1-bungarotoxin from the venom of Bungarus multicinctus (Taiwan-banded krait) |
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Authors: | L S Chang and C C Yang |
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Affiliation: | (1) Institute of Life Sciences, National Tsing Hua University, Hsinchu, Taiwan 30043, Republic of China |
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Abstract: | The N-terminal -amino groups of 1-bungarotoxin ( 1-Bgt) fromBungarus multicinctus venom were modified with trinitrobenzene sulfonic acid and the modified derivative was separated by high performance liquid chromatography. The trinitrophenylated (TNP) derivative contained two TNP groups at the -amino groups of A chain and B chain and showed a marked decrease in enzymatic activity. Methionine residues at positions 6 and 8 of the A chain were oxidized with chloramine T or cleaved with cyanogen bromide to remove the N-terminal octapeptide. Oxidation of methionine residues and removal of the N-terminal octapeptide caused a precipitous decrease in enzymatic activity, whereas antigenicity remained unchanged. The presence of dihexanoyllecithin influenced the interaction between 1-Bgt and 8-antilinonaphthalene sulfonate (ANS) and revealed that 1-Bgt consists of two types of ANS-binding sites, one at the substrate binding site of the A chain and the other might be at the B chain. The modified derivatives still retained their affinity for Ca2+ and ANS, indicating that the N-terminal region is not involved in Ca2+ and substrate binding. A fluorescence study revealed that the -amino group of the A chain was in the vicinity of substrate binding site and that the TNP -amino groups were in proximity to Trp-19 of the A chain. In addition, the study showed that the N-terminal region is important for stabilizing the architectural environment of Trp-19. The results, together with the proposal that Trp-19 of the A chain is involved in substrate binding, suggest that the N-terminal region of the A chain plays a crucial role in maintaining a functional active site for 1-Bgt. |
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Keywords: | snake venom presynaptic neurotoxin 1-bungarotoxin" target="_blank">gif" alt="beta" align="MIDDLE" BORDER="0">1-bungarotoxin role of N-terminal region in 1-bungarotoxin" target="_blank">gif" alt="beta" align="MIDDLE" BORDER="0">1-bungarotoxin |
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