A simple and inexpensive method for practical storage of field-sample proteins for subsequent MALDI-TOF MS analysis

Michael A Reeve,Alan G Buddie

doi:10.1186/s13007-018-0358-8

Abstract

BackgroundProtein-containing samples can readily be characterised and/or identified using matrix-assisted laser-desorption and ionisation time-of-flight mass spectrometry (MALDI-TOF MS). This technique however requires relatively-fresh biological material that contains proteins that have not yet undergone significant degradation. For field-work collection of samples, problems are often encountered due to delays between collection and sample processing, sample storage (possibly at elevated temperature and/or humidity in some climates), quarantine/regulatory restrictions on the transfer of living biological materials across national borders, and the potential to transfer unwanted microorganisms via non-living biological materials.ResultsIn an attempt to overcome the above difficulties, we have developed a simple and inexpensive method for practical storage of field-sample proteins, for subsequent MALDI-TOF MS analysis, in which biological material is crushed onto filter paper and dried. The dried and protein-impregnated filter paper can then be soaked in an alcoholic solution suitable for the inactivation of microorganisms of concern and again dried for storage. After subsequent dry storage, the proteins may be eluted from the paper using a solution containing acetonitrile, trifluoroacetic acid, water, and MALDI-TOF MS matrix near to saturation. The extracted proteins are then pipetted onto the MALDI-TOF MS sample plate for subsequent analysis. Using this method, spectra of comparable quality to fresh-material controls have been obtained for acid-soluble proteins from Fallopia japonica and Impatiens glandulifera leaf material. Unlike untreated leaf material, high-quality spectra can be obtained with and without alcohol treatment even after storage for one month at up to 40 °C.ConclusionsWe have developed a simple and inexpensive method for practical storage of field-sample proteins for subsequent MALDI-TOF MS analysis. Key benefits of this approach are a reduction in sample degradation, and consequent conservation of taxon-discriminatory spectral profiles, whilst minimising the potential for carryover of viable microorganisms.

Highlights

Protein-containing samples can readily be characterised and/or identified using matrix-assisted laser-desorption and ionisation time-of-flight mass spectrometry (MALDI-TOF MS)
In an attempt to overcome the above difficulties, we sought to develop a simple and inexpensive method, for the practical storage of field-sample proteins for subsequent MALDI-TOF MS analysis, in which biological material is crushed onto filter paper and dried
We have developed a simple and inexpensive method for practical storage of field-sample proteins, for subsequent MALDI-TOF MS analysis, in which biological material is crushed onto filter paper and dried

Summary

Introduction

Protein-containing samples can readily be characterised and/or identified using matrix-assisted laser-desorption and ionisation time-of-flight mass spectrometry (MALDI-TOF MS). This technique requires relatively-fresh biological material that contains proteins that have not yet undergone significant degradation. The diagnosis of bacterial and yeast infections, has been a key driver behind the development of MALDI-TOF MS for the identification and/or characterisation of biological samples [4]. This area has been reviewed extensively by Clark et al [3], along with many common methods used for sample preparation. The resulting matrix-saturated lysate containing acidsolubilised proteins is dried down directly onto the MALDI-TOF MS sample plate, overlaid with additional matrix solution (if required), and analysed

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Discussion

Conclusion