Activity of Anti-Microbial Peptides (AMPs) against Leishmania and Other Parasites: An Overview

Anti-microbial peptides (AMPs), small biologically active molecules, produced by different organisms through their innate immune system, have become a considerable subject of interest in the request of novel therapeutics. Most of these peptides are cationic-amphipathic, exhibiting two main mechanisms of action, direct lysis and by modulating the immunity. The most commonly reported activity of AMPs is their anti-bacterial effects, although other effects, such as anti-fungal, anti-viral, and anti-parasitic, as well as anti-tumor mechanisms of action have also been described. Their anti-parasitic effect against leishmaniasis has been studied. Leishmaniasis is a neglected tropical disease. Currently among parasitic diseases, it is the second most threating illness after malaria. Clinical treatments, mainly antimonial derivatives, are related to drug resistance and some undesirable effects. Therefore, the development of new therapeutic agents has become a priority, and AMPs constitute a promising alternative. In this work, we describe the principal families of AMPs (melittin, cecropin, cathelicidin, defensin, magainin, temporin, dermaseptin, eumenitin, and histatin) exhibiting a potential anti-leishmanial activity, as well as their effectiveness against other microorganisms.

Dynamical Oligomerisation of Histidine Rich Intrinsically Disordered ProteinS Is Regulated through Zinc-Histidine Interactions

Intrinsically disordered proteins (IDPs) can form functional oligomers and in some cases, insoluble disease related aggregates. It is therefore vital to understand processes and mechanisms that control pathway distribution. Divalent cations including Zn²⁺ can initiate IDP oligomerisation through the interaction with histidine residues but the mechanisms of doing so are far from understood. Here we apply a multi-disciplinary approach using small angle X-ray scattering, nuclear magnetic resonance spectroscopy, calorimetry and computations to show that that saliva protein Histatin 5 forms highly dynamic oligomers in the presence of Zn²⁺. The process is critically dependent upon interaction between Zn²⁺ ions and distinct histidine rich binding motifs which allows for thermodynamic switching between states. We propose a molecular mechanism of oligomerisation, which may be generally applicable to other histidine rich IDPs. Finally, as Histatin 5 is an important saliva component, we suggest that Zn²⁺ induced oligomerisation may be crucial for maintaining saliva homeostasis.

Histatin peptides: Pharmacological functions and their applications in dentistry

There are many human oral antimicrobial peptides responsible for playing important roles including maintenance, repairing of oral tissues (hard or soft) and defense against oral microbes. In this review we have highlighted the biochemistry, physiology and proteomics of human oral histatin peptides, secreted from parotid and submandibular salivary glands in human. The significance of these peptides includes capability for ionic binding that can kill fungal Candida albicans. They have histidine rich amino acid sequences (7-12 family members; corresponding to residues 12-24, 13-24, 12-25, 13-25, 5-11, and 5-12, respectively) for Histatin-3. However, Histatin-3 can be synthesized proteolytically from histatin 5 or 6. Due to their fungicidal response and high biocompatibility (little or no toxicity), these peptides can be considered as therapeutic agents with most probable applications for example, artificial saliva for denture wearers and salivary gland dysfunction conditions. The objectives of current article are to explore the human histatin peptides for its types, chemical and biological aspects. In addition, the potential for therapeutic bio-dental applications has been elaborated.

Salivary protein histatin 3 regulates cell proliferation by enhancing p27(Kip1) and heat shock cognate protein 70 ubiquitination

Histatins are salivary proteins with antimicrobial activities. We previously reported that histatin 3 binds to heat shock cognate protein 70 (HSC70), which is constitutively expressed, and induces DNA synthesis stimulation and promotes human gingival fibroblast (HGF) survival. However, the underlying mechanisms of histatin 3 remain largely unknown. Here, we found that the KRHH sequence of histatin 3 at the amino acid positions 5-8 was essential for enhancing p27(Kip1) (a cyclin-dependent kinase inhibitor) binding to HSC70 that occurred in a dose-dependent manner; histatin 3 enhanced the binding between p27(Kip1) and HSC70 during the G1/S transition of HGFs as opposed to histatin 3-M(5-8) (substitution of KRHH for EEDD in histatin 3). Histatin 3, but not histatin 3-M(5-8), stimulated DNA synthesis and promoted HGF survival. Histatin 3 dose-dependently enhanced both p27(Kip1) and HSC70 ubiquitination, whereas histatin 3-M(5-8) did not. These findings provide further evidence that histatin 3 may be involved in the regulation of cell proliferation, particularly during G1/S transition, via the ubiquitin-proteasome system of p27(Kip1) and HSC70.