Tyrocidine A interactions with saccharides investigated by CD and NMR spectroscopies

Abstract

Tyrocidines are a family of cyclic decapeptides produced by the soil bacterium, Brevibacillus parabrevis. These antibiotic peptides can be used to prevent infections in agriculture and food industry but also to prepare antimicrobial lozenges, creams, and dressings for medical applications. It has been observed that the tyrocidines interact with saccharides such as cellulose from their soil environment, as well as sugars in culture media and glycans in fungal cell walls. Here, we investigated the interactions of tyrocidines with glucose, sucrose, and cellotetraose (as cellulose model) in a quantitative fashion utilising CD and NMR spectroscopy. The CD and NMR spectra of tyrocidine A (TrcA) were analysed as a function of solvent composition, and the spectral properties agree with the formation of oligomeric structures that are governed by β-sheet secondary structures once the acetonitrile content of the solvent is increased. Saccharides seem to also induce TrcA spectral changes reverting those induced by organic solvents. The CD spectral changes of TrcA in the presence of glucose agree with new ordered H-bonding, possibly β-sheet structures. The amides involved in intramolecular H-bonding remained largely unaffected by the environmental changes. In contrast, amides exposed to the exterior and/or involved in TrcA intermolecular association show the largest 1 H chemical shift changes. CD and NMR spectroscopic investigations correlated well with TrcAglucose interactions characterized by a dissociation constant around 200 μM. Interestingly, the association of cellotetraose corresponds closely to the additive effect from four glucose moieties, while a much higher dissociation constant was observed for sucrose. Similar trends to TrcA for binding to the three saccharides were observed for the analogous tyrocidines, tyrocidine B, and tyrocidine C. These results therefore indicate that the tyrocidine interactions with the glucose monosaccharide unit are fairly specific and reversible.

The Influence of Cellulose-Type Formulants on Anti-Candida Activity of the Tyrocidines

“…The change in the first 60 min was investigated by measuring the total Trp fluorescence over the Trc mix dose-response concentration range (100 to 1.25 µg/mL) with E4M and A4M as representative cellulose formulants. Our results corroborated previous observations [ 34 , 36 , 39 , 40 , 46 ] that the Trc mix environment has a major influence on oligomerisation behaviour ( Figure 4 ).…”

“…The presence of four aromatic amino acid residues and three hydrophobic residues in tyrocidines (refer to Figure 1 C) could drive hydrophobic interactions in aqueous systems between the peptides to form oligomers. This oligomerisation leads to the change in their optical character, such as far-UV circular dichroism [ 40 , 46 ] and fluorescence emission [ 40 , 43 ], as well as possibly changing their biological activity.…”

“…The lower quantum yield of Trp could be due to either the exposure of the Trp residue to the polar solvent, polar groups in the celluloses, interaction with polar groups [ 32 ] (Lys 9 , Orn 9 , Gln 6 , Asn 5 and Tyr 7 side chains) and/or due to aromatic stacking [ 32 , 47 ]. Juhl et al [ 46 ] showed that D-Phe 1 , residue 4 (D-Trp 4 or D-Phe 4 ) and Orn 9 are most influenced by the interaction with glucose and its cellulose-type tetramer (cellotetraose), while Asn 5 and Tyr 7 are also influenced. A red-shifted emission maximum would be observed if the Trp residues were exposed to polar moieties in the formulants.…”

“…The observed association resulted in oligomerisation on the cellulose surface that depended on the peptide solvent system, as well as the absolute peptide concentration [ 45 ]. Juhl et al [ 46 ] showed that three of the Trcs, TrcA, B and C, interact specifically with glucose and cellotetraose. They observed that glucose influences the interpeptide hydrogen network, and therefore, oligomerisation.…”

Revealing the Mechanisms of Synergistic Action of Two Magainin Antimicrobial Peptides

“…Furthermore, other peptidic compounds with antimicrobial activities have been detected in microorganisms (7,8), but antimicrobial peptides also exist in many species of the plant and animal kingdom, including humans (9). The first of these peptides have been discovered decades ago and have been investigated ever since (4,(10)(11)(12). The list of amino acid sequences with antimicrobial activities is continuously increasing and they are accessible through various data bases (13)(14)(15)(16).…”