Comparative Metabolism of α‐ and β‐Peptides in the Insect Heliothis virescens and in Plant Cells of Black Mexican Sweet Maize

Abstract

The tripeptide H-Val-Ala-Leu-OH and the N-Ac-tetrapeptide amide Ac-Thr-Lys-Trp-Phe-NH2, and their beta-peptidic counterparts H-beta(3)hVal-beta(3)hAla-beta(3)hLeu-OH and Ac-beta(3)hThr-(S)beta(2)hLys-beta(3)hTrp-beta(3)hPhe-NH2, respectively, have been injected into Heliothis virescens larvae and added to cell cultures of black mexican sweet maize. The body liquids of the larvae and the supernatant of the plant cell cultures were sampled 0, 2, 3, 6, 17, and/or 24 h after application and analyzed by LC/MS. While the two alpha-peptides were degraded rapidly in these environments, the concentration of the beta-peptides was found to decrease very slowly. Thus, ca. 60% of the original amount of the beta-tetrapeptide was detected in the liquids of the insect after 24 h. The plant cells did not seem to make use of the beta-peptides at all, whereas, the alpha-tripeptide completely disappeared from the supernatant after 3 h. Thus, we have demonstrated, for the first time, the high stability of beta-peptides against degradation and metabolism in an insect and a plant. Especially remarkable is the persistence of the beta-tetrapeptide with its functionalised and, thus, 'metabolisable' side chains of Thr, Lys, Trp, and Phe in the insect larvae, which are known to have a high level of activity of oxidizing enzymes. The results described here match those of ADME investigations with radioactively labeled beta-peptides in rats, where essentially complete stability has been observed, while environmental microorganisms have been found to biodegrade beta-peptides, albeit slowly. Possible implications of these findings for biomedical and pest-control applications are proposed.

The Proteolytic Stability of ‘Designed’β-Peptides Containingα-Peptide-Bond Mimics and of Mixedα,β-Peptides: Application to the Construction of MHC-Binding Peptides

“…No evidence was found to suggest that any of the peptides were cleaved by pepsin or proteinase K. Both of these enzymes prefer hydrophobic residues in the P1 and P1' cleavage positions, so this result is perhaps not wholly surprising 17 ). In any case, the knowledge about specificities of peptidases for given peptide bonds derives from studies involving pure, natural apeptides: the same preferences may not be reflected in mixed a,b-peptides, nor for that matter in pure b-peptides.…”

“…± Studies performed to date have shown that b-peptides [1 ± 7] containing b-amino acids that possess natural side-chain groups are unambiguously stable to the action of several peptidases of broad substrate specificity [8 ± 14] 4 ). In addition, b-peptides are stable to metabolism by rats [16] and insects [17], although environmental microbial samples have been shown to utilize a b-tripeptide as the sole nitrogen and carbon source [18] [19].…”

The World of β‐ and γ‐Peptides Comprised of Homologated Proteinogenic Amino Acids and Other Components

“…Once it had become clear that b-peptides were not cleaved by peptidases, we carried out in vivo tests in rats [231], in insect larvae [512], and in maize cell cultures [512]. These investigations were conducted in close collaboration with colleagues at Novartis (primarily H. Wiegand, Basel) [231] and Syngenta (R. Lind, Jealott×s Hill, UK) [378] [512].…”

ADME Investigations of Unnatural Peptides: Distribution of a 14C‐Labeled β 3‐Octaarginine in Rats

“…Finally, incorporation of b-amino acid residues into peptides or proteins leads to overall structural changes that confer upon them stability against proteolytic cleavage; there are numerous highly physiologically active, often toxic natural products containing one or two, sometimes more b-amino acid moieties, incorporated by the non-ribosomal peptide-synthesis (NRPS) modules [18] (for leading references, see recent review articles on b-amino acids and peptides thereof [19]). A novel type of peptide, the bpeptides, built entirely of homologated proteinogenic amino acids, have been shown to be stable in vitro and in vivo (most microorganisms [20] [21], plants [22], insects [22], rodents [23]) (see A and B). Even mixed a/b-peptides of certain sequences C are stable to proteolytic cleavage [24].…”