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Racemization and Isomerization of Aspartyl Residues in Amyloid Peptides Involved in the Development of Alzheimer’s Disease
Published in Sara C. Zapico, Mechanisms Linking Aging, Diseases and Biological Age Estimation, 2017
Koichi Inoue, Toshimasa Toyo’oka
The N-terminal structure of the Aβ peptides, extracted from senile plaques such neuritic deposits, showed the cleaved Asp of about 8%, the formation of the isoaspartate form iso-Asp of about 20%, pyroglutamate-3 (p3Glu), the cyclization of the N-terminal glutamyl residue of about 51% and the native form of only about 20% by amino acid analysis and MS analysis (Kuo et al. 1997). These pathways of the post-translational N-terminal modification of Aβ are characterized to represent the most frequent type of aging protein damage. These reactions proceed through the formation of a cyclic succinimide intermediate, which rapidly undergoes spontaneous chemical modifications, such as AAR and AAI, during the degradation of Asp included peptides (Fig. 5) (Shimizu et al. 2000). During the spontaneous chemical modification of the Aβ peptides, the functionality of the AAR and AAI of Asp is to act as a specific repair system based on the PIMT (Shimizu et al. 2005). However, the PIMT repair system is not completely efficient due to the fact that the D-Asp residue is not recognized and is not equally functional in all tissues (Lowenson and Clarke 1991, 1992). It has been reported that the modified Asp sequence dramatically increased with aging in the brain (David et al. 1998). The AAR and AAI represent the major non-enzymatic and chemical modifications affecting the Aβ folding and degradation in the pathology of aging dementia. Recently, an interesting study was reported that when iso-Asp is present at position 672 in the APP, cathepsin B can catalyze the cleavage between methionine (Met) at 671 and isoAsp at 672 with a high efficiency (Böhme et al. 2008). Since the spontaneous AAI cannot readily take place in the post-translational N-terminal modification, the iso-Asp formation in the native Aβ can only occur as an early event in the Aβ production before the BACE1. This means that the detection of AAR and AAI in the N-terminal sequence has two aspects used to evaluate the production and aggregation of the Aβ peptides. In any case, the consequences of these chemical modifications are site-specific and can affect the age-related accumulation according to the structural alterations produced by the site-specific incorporation of the modified N-terminal residues. There have been many studies of the AAR and AAI events of Aβ peptides in vivo and/or vitro, but its role in the natural Aβ peptides pathogenesis in the focal brain tissues is still unclear.
Engineering an anti-CD52 antibody for enhanced deamidation stability
Published in mAbs, 2019
Huawei Qiu, Ronnie Wei, Julie Jaworski, Ekaterina Boudanova, Heather Hughes, Scott VanPatten, Anders Lund, Jaime Day, Yanfeng Zhou, Tracey McSherry, Clark Q. Pan, Rebecca Sendak
Deamidation of asparagine (Asn) residues is a major post-translational modification that can significantly impact protein structure and function.11,12 The non-enzymatic modification proceeds via formation of a five-member ring succinimide intermediate, which is subsequently hydrolyzed into a mixture of isoaspartate (isoAsp) and aspartate (Asp). The intermediate and the final products formed in the deamidation process lead to mass change, charge heterogeneity, and structural alteration of the peptide backbone in the case of isoAsp formation.13,14 Multiple factors have been identified that affect the rate of asparagine deamidation. With regard to the primary sequence, deamidation rates depend on the amino acid residues adjacent to Asn in the peptide chain, with Gly and Ser the most destabilizing C-terminal amino acids.12 The rate of deamidation also depends on external factors, increasing with elevated temperature and pH in general. More evidence suggests that deamidation can also happen at non-canonical sequences, when asparagine is followed by other amino acids.7,15 The three-dimensional structure has been found to be another major determining factor,12,14,16 but a detailed understanding of the correlation has been largely lacking. Protein interaction is also found to affect deamidation. For example, an isoaspartate product has been detected in the complementarity-determining region (CDR) region of a free antibody, but was completely missing in the antibody-antigen complex.17
Mass spectrometry analysis of the diversity of Aβ peptides: difficulties and future perspectives for AD biomarker discovery
Published in Expert Review of Proteomics, 2018
Natalia V. Zakharova, Anna E. Bugrova, Alexey S. Kononikhin, Maria I. Indeykina, Igor A. Popov, Eugene N. Nikolaev
Among the variety of endogenous and exogenous effectors of AD progression, amyloid-beta (Aβ)-soluble neurotoxic oligomers have been considered as the most powerful agents, which trigger the formation of Aβ plaques in the brain and cause neuron destruction [1]. Some of the post-translational Aβ modifications (PTMs) have been shown to enhance its oligomerization. A special role was suggested for modifications of the zinc-binding domain [2,3], and particular effects were concluded for pyroglutamate-3, isoaspartate-7, and/or phosphoserine-8 isoforms [4–6]. Recent human brain immunostaining experiments imply a more close relation of pyroglutamate-3 isoform to AD due to its accumulation inside the neurons, while the preferential localization of the isoaspartate-7 carrying isoform in the vessel walls was suggested to correlate with aging [7,8]. At the same time, MS studies of Aβ from human AD brains demonstrated a wide diversity of Aβ peptides, with 26 unique N- and C-terminal truncated proteoforms, among which the canonical Aβ1-42/1-40 comprised only ~15% [9]. Also the N-terminal truncated proteoforms are believed to predominate in the insoluble material, and C-terminal truncations are segregated into soluble aggregates. Besides this, Aβ N-terminal truncation has been considered as another possible reason of toxicity upon AD progression, whereas the non-AD senile and vascular plaques were shown to consist of only non-truncated Aβ 1-40/1-42 peptides [9].
Structure Based Prediction of Asparagine Deamidation Propensity in Monoclonal Antibodies
Published in mAbs, 2018
Qingrong Yan, Maggie Huang, Michael J. Lewis, Ping Hu
Deamidation of neutrally charged asparagine (Asn) residues to negatively charged aspartate (Asp) or isoaspartate (isoAsp) residues is a common degradation pathway that occurs during the manufacturing and storage of monoclonal antibodies (mAbs). Deamidation of several Asn residues in the complementary-determining regions (CDRs) of IgG mAbs have been reported to affect antigen binding.1–4 Recent studies have also shown that changes in the charge distribution on the protein surface could alter mAb pharmacokinetics (PK) by affecting FcRn-IgG dissociation.5,6 Thus, the potential risk of deamidation at each site needs to be evaluated to ensure product stability.