Macrocyclic Antimicrobial Peptides Engineered from ω-Conotoxin

Abstract

The potent calcium channel blocker ω-conotoxin MVIIA is a linear cystine-knot peptide with multiple basic amino acids at both termini. This work shows that macrocyclization of MVIIA linking two positive-charge terminal clusters as a contiguous segment converts a conotoxin into an antimicrobial peptide. In addition, conversion of disulfide bonds to amino butyric acids improved the antimicrobial activity of the cyclic analogs. Ten macrocyclic analogs, with or without disulfide bonds, were prepared by both Boc and Fmoc chemistry using native chemical ligation. All cyclic analogs were active against selected Gram-positive and Gram-negative bacteria with minimal inhibitory concentrations in a low μM range. In contrast, MVIIA and its linear analog were inactive at concentrations up to 0.5 mM. The cyclic analogs also showed 2 to 3-fold improved chemotactic activity against human monocytes THP-1 compared with MVIIA. Reduction of molecular stability against thermal and acid treatment due to the reduced number of disulfide crosslinks can be partly restored by backbone cyclization. Together, these results show that macrocyclization and side chain modification of a linear conopeptide lead to a gain-of-function, which brings a new perspective in designing and engineering of peptidyl therapeutics.

Keywords: Macrocyclization; antimicrobial peptide; chemotaxis.; cyclic conotoxin.

Scheme 1

Synthesis schemes of cyclic conotoxins with 0-2 disulfide bonds.

Fig. (1)

Chemical synthesis of reduced cyclic cM1B 8a on TEBA resin using Fmoc chemistry.

Fig. (2)

Chemotactic effect of MVIIA and cyclic analogs on human monocyte cell-line THP-1.

Fig. (3)

Acid and heat stability of MVIIA and its linear and cyclic analogs.