Identification of ᴅ-amino acid-containing peptides in human serum.

Seongmin Ha,Noriko Fujii,Minoru Suzuki,Masaharu Isoyama,Ingu Kim,Tadatoshi Kinouchi,Takumi Takata,Salvatore V Pizzo

doi:10.1371/journal.pone.0189972

Seongmin Ha, Noriko Fujii + Show 6 more

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https://doi.org/10.1371/journal.pone.0189972

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Abstract

Biologically uncommon d-aspartate (d-Asp) residues have been shown to accumulate in proteins associated with age-related human disorders, such as cataract and Alzheimer disease. Such d-Asp-containing proteins are unlikely to be broken down completely because metabolic enzymes recognize only proteins or peptides composed exclusively of l-amino acids. Therefore, undigested d-Asp-containing peptides may exist in blood and, if detectable, may be a useful biomarker for associated diseases. In this study, we investigated d-amino acid-containing peptides in adult human serum by a qualitative d-amino acid analysis based on a diastereomer method and LC-MS/MS method. As a result, two d-Asp-containing peptides were detected in serum, both derived from the fibrinogen β-chain, a glycoprotein that helps in the formation of blood clots. One of the peptides was fibrinopeptide B, which prevents fibrinogen from forming polymers of fibrin, and the other was same peptide with C-terminal Arginine missing. To our knowledge, this is the first report of the presence of d-amino acid-containing peptides in serum and the approach described will provide a new direction on the serum proteome and fragmentome.

Highlights

Amino acids have two optical isomers, the L-form and the D-form, living organisms on earth are composed exclusively of L-amino acids
An excellent study recently demonstrated that free D-amino acids in animal milks can be distinguished from their L-amino acid counterparts by UP-HPLC coupled with ion-mobility high-resolution MS (IM-HRMS) [12]
Two milliliters of 0.1% (v/ v) trifluoroacetic acid (TFA) solution was added to the remaining serum, which was applied to reversed-phase liquid chromatography (RP-HPLC)

Summary

Introduction

Amino acids have two optical isomers, the L-form and the D-form, living organisms on earth are composed exclusively of L-amino acids. Improvements in analytical techniques have facilitated an accurate analysis of amino acid enantiomers. D-amino acids have been detected in various living higher organisms both as a free molecule [1,2,3,4,5,6], and in peptides [7,8,9] and proteins [10, 11]. D-Amino acids have been conventionally detected by gas chromatography or RP-HPLC. An excellent study recently demonstrated that free D-amino acids in animal milks can be distinguished from their L-amino acid counterparts by UP-HPLC coupled with ion-mobility high-resolution MS (IM-HRMS) [12]

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