Consequences of Periodic α-to-β³ Residue Replacement for Immunological Recognition of Peptide Epitopes

Abstract

Oligomers that contain both α- and β-amino acid residues, or “α/β-peptides”, have emerged as promising mimics of signal-bearing polypeptides that can inhibit or augment natural protein–protein interactions. α/β-Peptides that contain a sufficient proportion of β residues evenly distributed along the sequence can be highly resistant to enzymatic degradation, which is favorable with regard to in vivo applications. Little is known, however, about recognition of α/β-peptides by the immune system. Prior studies have focused almost entirely on examples that contain a single β residue; such α/β-peptides frequently retain the immunological profile of the analogous α-peptide. We have conducted α-peptide vs α/β-peptide comparisons involving higher β residue content, focusing on molecules with αααβ and ααβαααβ backbone repeat patterns. Among analogues of an 18-mer derived from the Bim BH3 domain and an 8-mer derived from secreted phospholipase-2 (sPLA2), we find that recognition by antibodies raised against the prototype α-peptide is suppressed by periodic α → β replacements. Complementary studies reveal that antibodies raised against Bim BH3- or sPLA2-derived α/β-peptides fail to recognize prototype α-peptides displaying identical side chain repertoires. Because polypeptides containing d-α-amino acid residues are of growing interest for biomedical applications, we included the enantiomer of the sPLA2-derived α-peptide in these studies; this d-peptide is fully competent as a hapten, but the resulting antibodies do not cross react with the enantiomeric peptide. Among analogues of the 9-mer CD8+ T-cell viral epitope GP33, we observe that periodic α → β replacements suppress participation in the MHC I + peptide + T-cell receptor ternary complexes that activate cytotoxic T-lymphocytes, due in part to disruption of MHC binding.

Development of Potent, Protease-Resistant Agonists of the Parathyroid Hormone Receptor with Broad β Residue Distribution

“…6 This pursuit offers many opportunities for chemical innovation, 7 but progress to date has been limited, particularly in terms of establishing efficacy in vivo 8–14 and characterizing immune responses. 15, 16 Our own efforts have focused on peptidic oligomers that contain both α- and β-amino acid residues (α/β-peptides). 17–21 We recently demonstrated that α/β analogues of two hormones, glucagon-like peptide-1 (GLP-1) and parathyroid hormone (PTH), can serve as potent agonists of the cognate receptors, the GLP-1R and the PTHR1, respectively, in cell-based assays, 12, 13, 22 and these compounds are active in mice.…”

Backbone Modification of a Parathyroid Hormone Receptor-1 Antagonist/Inverse Agonist

“…Despite these favorable in vitro findings, however, we did not observe enhanced action of the α/β-peptide in vivo . It is currently not possible to test directly whether 2 persists for longer in the bloodstream than 1 because methods commonly used to detect PTH peptides in the bloodstream rely either on recognition of PTH fragments with specific antibodies, which are not usually suitable for detecting α/β-peptides, 57 or on a bioassay approach to assess PTHR1-based signaling activity present in blood samples 42 , which so far is not feasible for PTHR1 antagonists.…”

Rotamer Libraries for the High-Resolution Design of β-Amino Acid Foldamers

“…Furthermore, since structural data on non-natural residues is very limited, general rotamer libraries for these moieties must be simulation derived. Peptides entirely composed of or containing β-amino acids (Figure 1) possess useful pharmacological properties, particularly slow proteolytic degradation and a curbed immune response (Cheloha et al, 2015). Such molecules have been used to mimic apolipoprotein (Werder et al, 1999) and as antimicrobial compounds (Raguse et al, 2003); they may target mdm2 (Kritzer et al, 2004), the GLP-1 receptor (Denton et al, 2013), or HIV fusion (Bautista et al, 2009).…”