Hemin and bile pigments are the secondary structure regulators of intrinsically disordered antimicrobial peptides

Abstract

The interaction of protoporphyrin compounds of human origin with the major bee venom component melittin (26 a.a., Z +6) and its hybrid derivative (CM15, 15 a.a., Z +6) were studied by a combination of various spectroscopic methods. Throughout a two-state, concentration-dependent process, hemin and its metabolites (biliverdin, bilirubin, bilirubin ditaurate) increase the parallel β-sheet content of the natively unfolded melittin, suggesting the oligomerization of the peptide chains. In contrast, α-helix promoting effect was observed with the also disordered but more cationic CM15. According to fluorescence quenching experiments, the sole Trp residue of melittin is the key player during the binding, in the vicinity of which the first pigment molecule is accommodated presumably making indole-porphyrin π-π stacking interaction. As circular dichroism titration data suggest, cooperative association of additional ligands subsequently occurs, resulting in multimeric complexes with an apparent dissociation constant ranged from 20 to 65 μM. Spectroscopic measurements conducted with the bilirubin catabolite urobilin and stercobilin refer to the requirement of intact dipyrrinone moieties for inducing secondary structure transformations. The binding topography of porphyrin rings on a model parallel β-sheet motif was evaluated by absorption spectroscopy and computational modeling showing a slipped-cofacial binding mode responsible for the red shift and hypochromism of the Soret band. Our results may aid to recognize porphyrin-responsive binding motifs of biologically relevant, intrinsically disordered peptides and proteins, where transient conformations play a vital role in their functions.

The lipid mediator lysophosphatidic acid induces folding of disordered peptides with basic amphipathic character into rare conformations

“…Our results comparing several lipids above have demonstrated that LPA exerts specific interaction with the investigated peptides, which does not depend merely on its physicochemical properties, as structurally related lysophospholipids have not induced significant structural changes as LPA. Note, that similar selectivity was observed recently in our group when exploring interactions of disordered cationic AMP sequences with small anionic organic molecules, and endogenous bile pigments of hemin and its metabolites 47 , 48 . These studies represent several groups of compounds with similar molecular setup, nevertheless, in all groups we found both compounds which induced drastic conformational changes on AMPs and compounds showing nearly no interaction with the investigated peptides.…”

Disorder-to-helix conformational conversion of the human immunomodulatory peptide LL-37 induced by antiinflammatory drugs, food dyes and some metabolites

“…As it has been shown in our previous reports, the secondary structure of cationic AMPs can deeply be altered by various small molecules [14,15]. Some anionic pharmaceutical agents as well as endogenous metabolites (hemin, bile pigments) were able to induce disorder-to-helix transitions of the bee venom component melittin and its semisynthetic derivative.…”

Drug Conjugation Induced Modulation of Structural and Membrane Interaction Features of Cationic Cell-Permeable Peptides

“…According to our previous data [48][49][50], small-molecule-binding-induced disorder-to-helix transitions of cationic AMPs are associated with characteristic CD spectral alterations: In the very first phase of the titration with the folding inducer, the negative CD band of the peptide below 210 nm loses intensity, and its λ min is shifted to longer wavelengths. Similar changes were reported for TFE titration of intrinsically disordered peptides [51] and protein regions [52,53].…”