UHPLC-MS/MS Quantification of Human Cytosolic Aldehyde Oxidase: Heat-Assisted In-Solution Protein Denaturation and...

Area of Science:

• Biochemistry and Proteomics
• Analytical Chemistry
• Mass Spectrometry

Background:

• Accurate protein quantification via UHPLC-MS/MS relies heavily on effective protein denaturation and digestion.
• Previous methods for human aldehyde oxidase 1 (AOX1) lacked detailed sample preparation protocols, hindering reproducibility.
• A need existed for an optimized sample preparation method for quantifying cytosolic AOX1.

Purpose of the Study:

• To develop and optimize a sample preparation method for the UHPLC-MS/MS quantification of human cytosolic AOX1.
• To improve the yield and quality of the surrogate peptide ⁴⁴⁶VFFGEGDGIIR⁴⁵⁶ for AOX1 detection.

Main Methods:

• Evaluated various reagents and conditions for protein denaturation (urea, Rapigest, temperature, heating time, acetonitrile) and digestion (incubation time).
• Developed and validated a UHPLC-MS/MS assay for quantifying the AOX1 surrogate peptide and its stable-isotope-labelled internal standard.
• Utilized a high-temperature, in-solution denaturation protocol and optimized digestion parameters.

Main Results:

• Optimized denaturation (80°C, 15 min, DL-dithiothreitol) and digestion (4h) significantly improved surrogate peptide yield.
• A specific solvent composition (40% water-10% acetonitrile-50% ammonium bicarbonate) enhanced peptide solubility, linearity, and sensitivity.
• The validated UHPLC-MS/MS assay demonstrated high sensitivity (7.5 fmol), a broad linearity range (7.5-10,000 fmol), and short run time (11.5 min), meeting FDA guidelines.

Conclusions:

• Novel methodological advances, including high-temperature denaturation and optimized digestion, enable femtomole quantification of human cytosolic AOX1.
• The developed UHPLC-MS/MS method offers superior assay performance compared to previous approaches for AOX1 quantification.
• This optimized protocol provides a robust and sensitive method for analyzing human AOX1 in cellular samples.