Abstract
While natural intoxications with seeds of Ricinus communis (R. communis) have long been known, the toxic protein ricin contained in the seeds is of major concern since it attracts attention of those intending criminal, terroristic and military misuse. In order to harmonize detection capabilities in expert laboratories, an international proficiency test was organized that aimed at identifying good analytical practices (qualitative measurements) and determining a consensus concentration on a highly pure ricin reference material (quantitative measurements). Sample materials included highly pure ricin as well as the related R. communis agglutinin (RCA120) spiked into buffer, milk and meat extract; additionally, an organic fertilizer naturally contaminated with R. communis shred was investigated in the proficiency test. The qualitative results showed that either a suitable combination of immunological, mass spectrometry (MS)-based and functional approaches or sophisticated MS-based approaches alone successfully allowed the detection and identification of ricin in all samples. In terms of quantification, it was possible to determine a consensus concentration of the highly pure ricin reference material. The results provide a basis for further steps in quality assurance and improve biopreparedness in expert laboratories worldwide.
Highlights
The plant toxin ricin produced by Ricinus communis (R. communis) has been intensively studied since its identification in 1888 by Stillmark [1]
To set up a proper proficiency test (PT) test plan, nine samples were selected for further preparatory analysis taking into account the following (Table 1): (i) The samples needed to be detectable with a range of different techniques, as the PT was open with respect to the methods applied by the participants
Samples S2 to S8 were assessed as “correct/light green” if results were reported as “ricin and/or RCA120” without differentiation between ricin and RCA120 taking into account the following consideration: in case of an intentional release of toxins from Ricinus communis it would be important to detect the material as fast and reliable as possible in order to take adequate actions
Summary
The plant toxin ricin produced by Ricinus communis (R. communis) has been intensively studied since its identification in 1888 by Stillmark [1]. 60 kDa consisting of a catalytically active A-chain (~32 kDa) which acts as an RNA N-glycosidase and a sugar-binding B-chain (lectin, ~34 kDa) linked via a disulfide bond [2,3]. The study of ricin (RCA60) was complicated by the presence of a homologous protein in the seeds of R. communis identified as Ricinus communis agglutinin (RCA120), a much less toxic dimeric protein with high sequence identity to ricin. Whereas ricin is a monomeric AB toxin, R. communis agglutinin is a ~120 kDa dimer of two A- (~32 kDa) and
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