1. High level expression of the light chain of botulinum neurotoxin serotype C1 and an efficient HPLC assay to monitor its proteolytic activity
Richa Rawat, S Ashraf Ahmed, Subramanyam Swaminathan Protein Expr Purif. 2008 Aug;60(2):165-9. doi: 10.1016/j.pep.2008.03.010. Epub 2008 Mar 25.
Botulinum neurotoxins (serotypes BoNT/A-BoNT/G) induce botulism, a disease leading to flaccid paralysis. These serotypes are highly specific in their proteolytic cleavage of SNAP-25 (synaptosomal-associated protein of 25kDa), VAMP (vesicle associated membrane protein) or syntaxin. The catalytic domain (light chain, LC) of the neurotoxin has a Zn(2+) dependent endopeptidase activity. In order to design drugs and inhibitors against these toxins, high level overexpression and characterization of LC of BoNTs along with the development of assays to monitor their proteolytic activity becomes important. Using the auto-induction method, we attained a high level expression of BoNT/C1(1-430) yielding more than 30mg protein per 500ml culture. We also developed an efficient assay to measure the activity of serotype C1 based on a HPLC method. SNAP-25 with varying peptide length has been reported in literature as substrates for BoNT/C1 proteolysis signifying the importance of remote exosites in BoNT/C1 required for activity. Here, we show that a 17-mer peptide corresponding to residues 187-203 of SNAP-25, which has earlier been shown to be a substrate for BoNT/A, can be used as a substrate for quantifying the activity of BoNT/C1(1-430). There was no pH dependence for the proteolysis, however the presence of dithiothreitol is essential for the reaction. Although the 17-mer substrate bound 110-fold less tightly to BoNT/C1(1-430) than SNAP-25, the optimal assay conditions facilitated an increase in the catalytic efficiency of the enzyme by about 5-fold.
2. Discovery and design of novel inhibitors of botulinus neurotoxin A: targeted 'hinge' peptide libraries
J Hayden, J Pires, S Roy, M Hamilton, G J Moore J Appl Toxicol. 2003 Jan-Feb;23(1):1-7. doi: 10.1002/jat.870.
Intoxication by the zinc protease botulinus neurotoxin A (BoNT-A) results from cleavage of a single Q-R bond in the neuronal protein SNAP-25, which disables the docking mechanism required for neurotransmitter release. In the present study, potential inhibitors of BoNT-A were assessed from their effects on the BoNT-A cleavage of a synthetic 17-mer peptide (SNAP-25, residues 187-203) spanning the Q-R cleavage site. Compounds that inhibited BoNT-A included thiols (zinc chelators) such as dithiothreitol, dimercaptopropanesulfonic acid, mercaptosuccinic acid and captopril. In addition, compounds containing multiple acidic functions, such as the SNARE motif V2 (ELDDRADALQ), the tripeptide Glu-Glu-Glu and the steroid glycoside glycyrrhizic acid, were effective inhibitors. 'Hinge' peptide mini-libraries (PMLs) having the structure acetyl-X(1)-X(2)-linker-X(3)-X(4)-NH(2) or X(1)-X(2)-linker-X(3), where X(1)-X(4) were mixtures of selected amino acids and the flexible linker was 4-aminobutyric acid, also provided effective inhibition. Targeted PMLs containing the acidic amino acids Asp and Glu, the scissile-bond amino acids Gln and Arg and the zinc chelators His and Cys produced pronounced inhibition of BoNT-A. Deconvolution of these libraries will provide novel ligands with improved inhibitory potency as leads in the design of peptide mimetics to treat BoNT poisoning.
3. Synthesis of substrates and inhibitors of botulinum neurotoxin type A metalloprotease
C Sukonpan, T Oost, M Goodnough, W Tepp, E A Johnson, D H Rich J Pept Res. 2004 Feb;63(2):181-93. doi: 10.1111/j.1399-3011.2004.00124.x.
Botulinum neurotoxin (BoNT) metalloproteases and related proteases are the most selective proteases known. X-ray crystal structures suggest that the active sites of the native enzymes exist in catalytically incompetent forms that must be activated by substrate binding. In order to characterize the postulated substrate-induced conformational changes for enzyme activation, we synthesized a series of transition-state analog inhibitors in which the dipeptide cleavage site is replaced by tetrahedral intermediate analogs within the minimal substrate peptide sequence. In this paper, we report our efforts to design inhibitors of BoNT/A metalloprotease. We confirm that an effective substrate sequence for BoNT/A metalloprotease is a 17-mer peptide corresponding to residues 187-203 of SNAP-25. A more stable substrate, Nle202SNAP-25 [187-203] was synthesized in order to develop an assay for proteolytic activity of BoNT/A metalloprotease that can be used to monitor time-dependent inhibition. Alpha-thiol amide analogs of Gln-197 were incorporated via solid-phase peptide synthesis into both 17-mer minimal peptide substrate sequences. The synthesis, characterization and inhibition kinetics for the alpha-thiol amide analogs of holotoxin A substrate are described. These substrate-derived inhibitors were shown to be submicromolar inhibitors of BoNT/A catalytic activity.
