Age-related isomerization of Asp in human immunoglobulin G kappa chain

isoAsp-Quest: workflow development for isoAsp identification using database searches

A recent study reported that isomerization of aspartyl residues (Asp) occurs in various tissues and proteins in vivo. For a comprehensive analysis of post-translational modifications, the mass spectrometry (MS)-based proteomic approach is a straightforward method; however, the isomerization of Asp does not alter its molecular weight. Therefore, a unique method is required to analyse Asp isomers using MS. Herein, we present a novel strategy, isoAsp-Quest, which is a database search-oriented isoAsp identification method. isoAsp is specifically converted to 18O-labelled Lα-Asp by the enzymatic reaction of protein L-isoaspartyl-O-methyltransferase (PIMT) in 18O water with a mass shift of 2 Da, which, in principle, enables us to distinguish Asp isomers. However, in practise, a labelled Lα-Asp signal overlaps with that of endogenous Lα-Asp, making detection challenging. Therefore, degradation of the endogenous Lα-Asp peptide by AspN and subsequent removal of AspN were performed prior to the PIMT reaction. This strategy was applied to bovine lens α-crystallin. Consequently, several Asp isomerization sites, consistent with human αA-crystallin, were identified in bovine αA-crystallin, indicating that this strategy is also effective for biological proteins. Therefore, isoAsp-Quest enables the analysis of Lβ-Asp in a straightforward and rapid workflow, which may be useful for the quality control of protein products and biomarker discovery.

Stability of Protein Pharmaceuticals: Recent Advances

There have been significant advances in the formulation and stabilization of proteins in the liquid state over the past years since our previous review. Our mechanistic understanding of protein-excipient interactions has increased, allowing one to develop formulations in a more rational fashion. The field has moved towards more complex and challenging formulations, such as high concentration formulations to allow for subcutaneous administration and co-formulation. While much of the published work has focused on mAbs, the principles appear to apply to any therapeutic protein, although mAbs clearly have some distinctive features. In this review, we first discuss chemical degradation reactions. This is followed by a section on physical instability issues. Then, more specific topics are addressed: instability induced by interactions with interfaces, predictive methods for physical stability and interplay between chemical and physical instability. The final parts are devoted to discussions how all the above impacts (co-)formulation strategies, in particular for high protein concentration solutions.'

The chiral proteomic analysis applied to aging collagens by LC-MS: Amino acid racemization, post-translational modifications, and sequence degradations during the aging process

Collagen is the most abundant protein in the animal and human bodies, and it is not exempt from this aging phenomenon. Some age-related changes may appear on collagen sequences, such as increased surface hydrophobicity, the appearance of post-translational modifications, and amino acids racemization. This study has shown that the protein hydrolysis under deuterium conditions is privileged to limit the natural racemization during the hydrolysis. Indeed, under the deuterium condition, the homochirality of recent collagens is preserved whose amino acids are found in their L-form. However, in aging collagen, a natural amino acid racemization was observed. These results confirmed that the % d-amino acids are progressive according to age. The collagen sequence is degraded over time, and a fifth of the sequence information is lost during aging. Post-translational modifications (PTMs) in aging collagens can be a hypothesis to explain the modification of the hydrophobicity of the protein with the decrease of hydrophilic groups and the increase of hydrophobic groups. Finally, the exact positions of d-amino acids and PTMs have been correlated and elucidated.

Site-specific amino acid D-isomerization of Tau R2 and R3 peptides changes the fibril morphology, resulting in attenuation of Tau aggregation inhibitor potency

Tau, a microtubule-binding protein, is a major component of neurofibrillary tangles in the brains of Alzheimer's disease patients. Tau aggregation following fibril formation induces Alzheimer's disease pathogenesis. The accumulation of D-isomerized amino acids in proteins that occurs in several tissues with aging is thought to be implicated in age-related diseases. D-isomerized Asp accumulation has also been found in Tau in neurofibrillary tangles. We previously demonstrated the effects of D-isomerization of Asp within microtubule-binding repeat peptides of Tau, Tau R2, and R3 on the rates of structural transition and fibril formation. Here, we investigated the potency of Tau aggregation inhibitors on fibril formation of wild-type Tau R2 and R3 peptides and D-isomerized Asp-containing Tau R2 and R3 peptides. D-isomerization of Asp within Tau R2 and R3 peptides attenuated the potency of inhibitors. We next investigated the fibril morphology of D-isomerized Asp-containing Tau R2 and R3 peptides by electron microscopy. D-isomerized Asp-containing Tau R2 and R3 fibrils showed significantly different fibril morphology from that of wild-type peptides. Our results indicate that D-isomerization of Asp within Tau R2 and R3 peptides affects fibril morphology, resulting in attenuation of the potency of Tau aggregation inhibitors.

Recent Advances in Chiral Analysis of Proteins and Peptides

Like many biological compounds, proteins are found primarily in their homochiral form. However, homochirality is not guaranteed throughout life. Determining their chiral proteinogenic sequence is a complex analytical challenge. This is because certain d-amino acids contained in proteins play a role in human health and disease. This is the case, for example, with d-Asp in elastin, β-amyloid and α-crystallin which, respectively, have an action on arteriosclerosis, Alzheimer’s disease and cataracts. Sequence-dependent and sequence-independent are the two strategies for detecting the presence and position of d-amino acids in proteins. These methods rely on enzymatic digestion by a site-specific enzyme and acid hydrolysis in a deuterium or tritium environment to limit the natural racemization of amino acids. In this review, chromatographic and electrophoretic techniques, such as LC, SFC, GC and CE, will be recently developed (2018–2020) for the enantioseparation of amino acids and peptides. For future work, the discovery and development of new chiral stationary phases and derivatization reagents could increase the resolution of chiral separations.