Challenges in the Development of Reference Materials for Protein Toxins

Abstract

High molecular weight protein toxins produced by bacteria, e.g. staphylococcal enterotoxins and botulinum neurotoxins, as well as plant toxins such as ricin and abrin, are relevant analytes in different application areas: food safety, public health, civil security and defense sector, and – in case of botulinum neurotoxins – also in pharmaceutics. For their reliable and accurate detection, identification and quantification, reference materials (RMs), in particular certified reference material (CRM), are required. The present article focuses on challenges in the development (production and certification) of such RMs. Firstly, it highlights the role of RMs and CRMs, what they can be used for, the nature of certified properties, metrological traceability, and uncertainty of certified values, as well as commutability of RMs. Secondly, the molecule-specific technical challenges are highlighted using the example of the mentioned toxins. This includes for instance the choice of a suitable purification strategy (recombinant expression and purification versus the purification of toxin from natural sources), the in-depth characterization of the obtained preparations by a comprehensive set of methods including immunochemical assays, mass spectrometry, and functional assays to verify their identity and establish their purity and activity, and finally, suitable approaches for determining reference values of important toxin properties (protein mass concentration in solution, biological activity). The article summarizes ongoing activities in a new European initiative called EuroBioTox, which aims at the production and certification of RMs for selected protein toxins and the establishment of validated procedures for the detection and identification of biological toxins.