Rickey P. Hicks

The medicinal chemistry of botulinum, ricin and anthrax toxins.

The potential use of weapons of mass destruction (nuclear, biological or chemical) by terrorist organizations represents a major threat to world peace and safety. Only a limited number of vaccines are available to protect the general population from the medical consequences of these weapons. In addition there are major health concerns associated with a pre-exposure mass vaccination of the general population. To reduce or eliminate the impact of these terrible threats, new drugs must be developed to safely treat individuals exposed to these agents. A review of all therapeutic agents under development for the treatment of the illnesses and injuries that result from exposure to nuclear, biological or chemical warfare agents is beyond the scope of any single article. The intent here is to provide a focused review for medicinal and organic chemists of three widely discussed and easily deployed biological warfare agents, botulinum neurotoxin and ricin toxins and the bacteria Bacillus anthracis. Anthrax will be addressed because of its similarity in both structure and mechanism of catalytic activity with botulinum toxin. The common feature of these three agents is that they exhibit their biological activity via toxin enzymatic hydrolysis of a specific bond in their respective substrate molecules. A brief introduction to the history of each of the biological warfare agents is presented followed by a discussion on the mechanisms of action of each at the molecular level, and a review of current potential inhibitors under investigation.

PFG-NMR Investigations of the Binding of Cationic Neuropeptides to Anionic and Zwitterionic Micelles

Abstract The mechanism by which peptides bind to micelles is believed to be a two-phase process, involving (i) initial electrostatic interactions between the peptide and micelle surface, followed by (ii) hydrophobic interactions between peptide side chains and the micelle core. To better characterize the electrostatic portion of this process, a series of pulse field gradient nuclear magnetic resonance (PFG-NMR) spectroscopic experiments were conducted on a group of neuropeptides with varying net cationic charges (+1 to +3) and charge location to determine both their diffusion coefficients and partition coefficients when in the presence of detergent micelles. Two types of micelles were chosen for the study, namely anionic sodium dodecylsulfate (SDS) and zwitterionic dodecylphosphocholine (DPC) micelles. Results obtained from this investigation indicate that in the case of the anionic SDS micelles, peptides with a larger net positive charge bind to a greater extent than those with a lesser net positive charge (bradykinin > substance P > neurokinin A > Met-enkephalin). In contrast, when in the presence of zwitterionic DPC micelles, the degree of mixed-charge nature of the peptide affects binding (neurokinin A > substance P > Met-enkephalin > bradykinin). Partition coefficients between the peptides and the micelles follow similar trends for both micelle types. Diffusion coefficients for the peptides in SDS micelles, when ranked from largest to smallest, follow a trend where increasing net positive charge results in the smallest diffusion coefficient: Met-enkephalin > neurokinin A > bradykinin > substance P. Diffusion coefficients when in the presence of DPC micelles, when ranked from largest to smallest, follow a trend where the presence of negatively-charged side chains results in the smallest diffusion coefficient: bradykinin > Met-enkephalin > substance P > neurokinin A.

Modeling of the recognition site of the NK1 receptor

Abstract The tachykinin receptor, NK1, and its native neuropeptide ligand, substance P, are believed to play a major role in the biochemistry of inflammation and in the transmission of pain. The binding of substance P is known to involve extracellular as well as transmembrane regions of the NK1 receptor. Reported here is the design of a model of the recognition site of the second transmembrane domain of the NK1 receptor. Molecular mechanics calculations were employed to evaluate the potential of six polypeptides corresponding to the first, second and third transmembrane domains of the NK1 receptor, to bind with substance P. One of the most promising of these models contained 30 amino acid residues corresponding to part of the first extracellular region coupled to the second transmembrane domain. A model of reduced size (18 amino acid residues) that contains the correct type and location of the amino acid residues predicted to be involved in ligand binding was used to validate the results of the molecular mechanics calculations. One-dimensional proton NMR spectra acquired in DMSO-d6 indicated that this 18 amino acid residue polypeptide forms a complex with substance P.

Preparation of Membrane Models of Gram-Negative Bacteria and Their Interaction with Antimicrobial Peptides Studied by CD and NMR

The antibiotic activity of antimicrobial peptides is generally derived via some type of disruption of the cell membrane(s). The most common models used to mimic the properties of bacterial membranes consist of mixtures of various zwitterionic and anionic phospholipids. This approach works reasonably well for Gram-positive bacteria. However, since the membranes of Gram-negative bacteria contain lipopolysaccharides, as well as zwitterionic and anionic phospholipids, a more complex model is required to simulate the outer membrane of Gram-negative bacteria. Herein we present a protocol for the preparation of models of the outer membranes of the Gram-negative bacteria Klebsiella pneumoniae and Pseudomonas aeruginosa. This protocol can be used to prepare models of other Gram-negative bacteria provided the strain-specific lipopolysaccharides are available.

Characterization of [Re~2CL~3(mu-dppm)~2 (NCCH~3)~2] [Cl] and [Re~2Cl~3(mu-dppm)~2(NCC~6H~5)~2] [Cl] · 2CH~2Cl~2 by X-ray Crystallographic and Two-Dimensional NMR Spectroscopic Techniques

The complex Re2Cl6(P-n-Bu3)2 prepared in situ reacts with CH3CN to form a blue-green solution. Addition of the chelating phosphine bis(diphenylphosphino)methane (dppm) results in the formation of the complex [Re2Cl3(μ-dppm)2(NCCH3)2][Cl] (1) upon heating. The two acetonitrile molecules adopt a trans geometry on the rhenium center with the axially coordinated chlorine. The analogous trans benzonitrile species [Re2Cl3(μ-dppm)2(NCC6H5)2][Cl]·2CH2Cl2 (2) is synthesized under the same reaction conditions. The coupling constants of the AA′BB′ 31P{1H} NMR spectra of the compounds were elucidated from 31P–31P homonuclear J-resolved NMR experiments. Additional characterization methods include 31P{1H} NMR spectroscopy, UV-vis spectroscopy, and X-ray crystallography.