Bacterial Zinc Proteases and their Inhibition

Claudiu      T. Supuran; Antonio      Mastrolorenzo

Abstract

There is a wealth of new data regarding zinc proteases present in many bacterial species, many of which cause serious disease, such as Listeria spp, Vibrio spp., Pseudomonas aeruginosa, Legionella pneumophila, Streptomyces spp., Clostridium spp., Enterococcus spp., etc. Many of these pathogens developed resistance to the clinically used antibiotics, which normally target bacterial cell wall biosynthesis or affect protein synthesis on ribosomes. Zinc-containing proteases play critical functions in these organisms, related to colonization and evasion of host immune defenses, acquisition of nutrients for growth and proliferation, facilitation of dissemination, or tissue damage during infection. However, only in the last decade such targets started to be investigated in detail. Thus, there are a lot of data available regarding the cloning, purification and biochemical characterization of many such zinc proteases, from both gram-positive as well as gram-negative pathogens. But for the moment, few potent and specific inhibitors for bacterial such proteases have been reported except for Clostridium histolyticum collagenase, botulinum and tetanus neurotoxin and anthrax lethal factor. No inhibitors of the critically important and ubiquitous IgA-specific metallopeptidases or AAA proteases have been reported to date, although such compounds would presumably constitute a new class of highly effective antibiotics. The clostridial neurotoxins, tetanus neurotoxin (TeNT) and botulinum neurotoxin (BoNT, of which seven distinct serotypes are known, BoNT/A-G), together with the anthrax lethal factor (LF) are zinc proteases and among the most toxic compounds known in Nature. The substrate of TeNT is a 120-residue protein anchored to the membrane of cell vesicles, which has been termed VAMP, whereas BoNTs/B, D, F and G cleave specifically VAMP at different single peptide bonds. BoNTs also possess two other intracellular targets in addition to VAMP: SNAP-25 (25 kDa synaptosomal-associated protein) and syntaxin, both of which are cleaved between Gln#Arg (by BoNT/A), Lys#Ala (by BoNT/C), Arg#Ala (by BoNT/C) or Gln#Lys (different neurotoxins) residues. The three proteases contain a Zn(II) ion coordinated by two His and a Glu residue, similarly to many other zinc proteases. Many different peptidomimetic and non-peptide inhibitors were discovered for the three enzymes, after the report of their X-ray crystal structures, alone or complexed to substrates/inhibitors. Such compounds, presently in clinical development, may be effective in case of terroristic attacks in which such toxins are used or to treat diseases provoked by these bacteria which are widespread in nature. Furthermore, BoNT A has many applications in medicine, for the management of dystonias, strabismus, facial wrinkling, brow position, as well as palmar and axillary hyperhidrosis. More recently, BoNT A was also shown to be useful in the symptomatic therapy of pain, together with disorders in which muscular hyperactivity plays a prominent role, such as for example glandular hypersecretion, lower urinary tract dysfunction, prostatic disorders and vaginismus in women suffering with pelvic floor muscle tension.

Keywords: Protease, zinc protease, antibacterial agent, Clostridium histolyticum collagenase, botulinum neurotoxin, tetanus neurotoxin, anthrax lethal factor, enzyme inhibitor, Vibrio collagenase, Axillary hyperhidrosis