A folding-dependent mechanism of antimicrobial peptide resistance to degradation unveiled by solution structure of distinctin

Abstract

Many bioactive peptides, presenting an unstructured conformation in aqueous solution, are made resistant to degradation by posttranslational modifications. Here, we describe how molecular oligomerization in aqueous solution can generate a still unknown transport form for amphipathic peptides, which is more compact and resistant to proteases than forms related to any possible monomer. This phenomenon emerged from 3D structure, function, and degradation properties of distinctin, a heterodimeric antimicrobial compound consisting of two peptide chains linked by a disulfide bond. After homodimerization in water, this peptide exhibited a fold consisting of a symmetrical full-parallel four-helix bundle, with a well secluded hydrophobic core and exposed basic residues. This fold significantly stabilizes distinctin against proteases compared with other linear amphipathic peptides, without affecting its antimicrobial, hemolytic, and ion-channel formation properties after membrane interaction. This full-parallel helical orientation represents a perfect compromise between formation of a stable structure in water and requirement of a drastic structural rearrangement in membranes to elicit antimicrobial potential. Thus, distinctin can be claimed as a prototype of a previously unrecognized class of antimicrobial derivatives. These results suggest a critical revision of the role of peptide oligomerization whenever solubility or resistance to proteases is known to affect biological properties.NMR structure ͉ oligomerization ͉ pore-forming peptide ͉ disulfide

The chains of the heterodimeric amphibian skin antimicrobial peptide, distinctin, are encoded by separate messenger RNAs

“…Comparative proteolytic degradation assays of distinctin and synthetic peptide analogues reported that distinctin is more resistant to serine protease breakdown as a heterodimer than as monomers or homodimers [19,20]. The situation in the P. burmeisteri skin secretion, with most of the distinctin occurring as a heterodimer, may reflect a similar situation.…”

“…Why the heterodimer prevails in the P. burmeisteri skin secretion remains an unanswered question, and we can only speculate at this time. Structure modeling and NMR studies on the similar distinctin chains of P. distincta has indicated that matching hydrophobic areas on the outer surfaces of chain A and B and alpha-helices, may play a role in bringing both chains together [19,[40][41][42]. These studies, however, did not look at the structure of the homodimers.…”

“…Previous investigations have assessed the antimicrobial activity of all possible forms of the closely-related P. distincta distinctins [19,20]. They found that the heterodimer has broadspectrum antimicrobial activity, and that the dimers (hetero-or homo-) are more active than the separate monomers.…”

“…The only example so far is distinctin, a 5.4 kDa heterodimer composed of two different peptide chains containing 22 and 25 residues, respectively, that was originally identified in the skin secretion of the phyllomedusine frog, P. distincta. It has antimicrobial activity against Gram-negative and Gram-positive bacteria [10,19,20], and the dimerization was found to enhance the peptides' bioactivity with respect to that of each monomer. In this context, heterodimeric peptides may represent a new class of amphibian skin peptide with potent biological/pharmacological activity that relies upon the formation of intermolecular complexes.…”

Crystallization, dehydration and experimental phasing of WbdD, a bifunctional kinase and methyltransferase fromEscherichia coliO9a

“…Both algorithms identified structures with similar arrangements of helices (e.g. PDB entries 1xkm, 2lfh and 3aha; Raimondo et al, 2005;Northeast Structural Genomics Consortium, unpublished work;Izumi et al, 2010), supporting the notion that the geometric arrangement of helices was reasonable. On this basis, we tentatively selected the hand.…”