Sequence-independent Control of Peptide Conformation in Liposomal Vaccines for Targeting Protein Misfolding Diseases

Abstract

Synthetic peptide immunogens that mimic the conformation of a target epitope of pathological relevance offer the possibility to precisely control the immune response specificity. Here, we performed conformational analyses using a panel of peptides in order to investigate the key parameters controlling their conformation upon integration into liposomal bilayers. These revealed that the peptide lipidation pattern, the lipid anchor chain length, and the liposome surface charge all significantly alter peptide conformation. Peptide aggregation could also be mod- The role of immunogen conformation in the specificity and efficacy of the humoral immune response has been recognized in a number of recent therapeutic and prophylactic vaccines (1-4). Conformation-specific antibodies generated by immunization with conformationally restricted immunogens are also important tools for disease diagnosis as biochemical probes for establishing protein structure-function relationships (5, 6) and in affinity purification (7,8). Development of such peptide immunogens, however, has thus far been hindered by the lack of general design strategies to control the conformation of a given peptide sequence. In addition, most naked peptides have low inherent immunogenicity. Although design of peptide templates for the generation of antibodies that selectively recognize protein epitopes with an ␣-helical conformation has been reported (2, 4, 9, 10), general strategies to design short peptide fragments as immunogens for targeting other protein conformations are lacking.Protein aggregation resulting from aberrant folding is characterized by the formation of proteinaceous deposits called amyloid, which exhibit ␤-sheet structure (11). Misfolding is now associated with over 20 human diseases, including Creutzfeldt-Jakob disease, Alzheimer disease (AD), 2 Huntington disease, and Type II diabetes mellitus (12). Vaccines that can elicit antibodies against only the pathological ␤-sheet multimers of these targets would thus be considered advantageous from an efficacy perspective but also particularly from a safety perspective, where the non-folded protein has physiological relevance. In AD, ␤-amyloid peptides (A␤) A␤(1-40) and A␤(1-42) have been associated with disease progression over several decades of research, and the ␤-sheet aggregates of A␤ are one of the major pathological hallmarks of AD (13). Although the molecular pathology of AD has not yet been elucidated, a large variety of soluble and insoluble ␤-sheet A␤(1-40/42) oligomers with different degrees of polymerization have been identified in vitro or in AD brain as synaptotoxic and likely causal agents of cognitive impairment (14 -18).The discovery that active vaccination of transgenic mice overexpressing human amyloid precursor protein (APP) with A␤-derived peptides could be an effective means to modify disease progression has opened up new vistas in AD therapy (19 -21). The importance of immunogen aggregation state upon immune response specificity has been demonstrated by the generation of an...

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