Role of Zinc Binding in Type A Botulinum Neurotoxin Light Chain's Toxic Structure

Publisher Website
Google Scholar
Abstract
Clostridial neurotoxins are zinc endopeptidases, and each contains one Zn2+/molecule. To investigate the structural/functional role of Zn2+ in botulinum neurotoxin light chain (the enzymatic subunit of the neurotoxin), the effect of the removal of zinc on protein folding and enzyme kinetics was investigated. The active site Zn2+, which was easily displaced from the active site by ethylenediaminetetraacetate, reversibly binds to the BoNT/A light chain (LC) in a stoichiometric manner. Enzymatic activity was completely abolished in the zinc-depleted light chain (apo-LC). However, Zn2+ replenishment partially restored the activity in the re-Zn2+-LC (kcat = 72 min-1) compared to the holo-LC (kcat = 140 min-1). Comparable Km values in the holo- and re-Zn2+-LC were observed (41 and 55 μM, respectively), indicating a similar substrate binding ability. We investigated the structural basis of a 3-fold difference in the catalytic efficiency of the native holo-LC and re-Zn2+-LC by analyzing secondary and tertiary structural parameters. Removal of the zinc causes irreversible tertiary structural change while the secondary structure remains unchanged. Zinc binding leads to enhanced thermal stability of the LC, which is not identical in the native holo-LC and re-Zn2+-LC.

This publication has 5 references indexed in Scilit: