Electronic Supplementary Material for the manuscript entitled: Effective selenium detoxification in the seed proteins of a hyperaccumulator plant: the analysis of selenium containing proteins of monkeypot nut ( Lecythis minor ) seeds by A. Németh and M. Dernovics, published in Journal of Biological Inorganic Chemistry Table S 2 Instrumental parameters of the HPLC-ESI-QTOF-MS set-up Accurate Mass QTOF LC-MS (Agilent) ESI sourceDual ESI (Agilent) Operational modePositive Precursor ion isolation in MS/MS modemedium (4 m/z) Mass accuracy< 2 ppm Mass resolution> Detection frequency 4 GHz Fragmentor voltage150 V/-150 V Curtain voltage65 V/ -65 V Drying gas13 L/min Capillary voltage800 V Nebulizer pressure40 psig Gas temperature325 ºC Data analysis softwareMass Hunter Acquisition B with SP3 Mass Hunter Qualitative Analysis B with SP3 Table S 1 Chromatographic parameters applied. ColumnXDB C18, 4.6 mm x 100 mm x 5 µm Injection volume (µL)10 Flow rate (mL min -1 )0.35 Buffer A0.1% formic acid in water Buffer Bacetonitrile with 0.1% formic acid Gradient program0-210% B 4up to 20% B 10up to 45% B 15up to 100% B 20100% B 22down to 10% B

Table S 4. Protein database search identification results. The coverage was calculated by the sotware based on the sequence of the precursor protein. In the case of 2S albumin and 2S sulfur-rich proteins, the signal and propeptides are removed during the maturation of the proteines. The revised coverages were calculated based on the sequence of the mature proteins. Methionine coverage is the coverage of methionine containing peptides. Se-containing peptides are highlighted. Accession number DescriptionOrganism Software coverage Calculated coverage Methionine coverage Peptides Sequencem/zzMassMass errorStartEnd Q84ND211S globulinB. excelsa VIRPP VQIVDHR HFFLAGNIQR CAGVAALR LYYVTGR NGETVFDDNLR VQHTASDLNQLDQNPR NTIRPQGLLLPVYTNAPK KGDIIAIPAGVALW GILGVLMPGCPETF GILGVLBPGCPETF LTTVNSLKVPILTF FIQNIDNPAEDFYNPR VPILTFLQL B6EU542S albuminB. excelsa1829 GEQMR CEGLR EMQPR GEQBR EBQPR QQMLSH pyro-QQBLSH CNLSPQR MAENLPSR BAENLPSR P S sulfur-rich storage protein 1 B. excelsa1532 GEQMR CEGLR EMQPR GEQBR EBQPR QQMLSH AENLPSR pyro-QQBLSH MQQEEMQPR BQQEEMQPR BQQEEBQPR QQBLSH P0C8Y8 2S sulfur-rich storage protein 2 B. excelsa51519 MYLR BYLR CEGLR CNLSPQR Table S 3. Database search and protein validation settings. Database search settings Name and version of the programPeptideShaker EnzymeTrypsin Fixed modificationCarbamidomethyl cysteine Variable modifications Phosphorylation of serine or tyrosine Oxidation of methionine Selenomethionine Selenocysteine Precursor mass tolerance10 ppm Fragment ion typesb and y Maximum missed cleavages2 Fragment mass tolerance0.05 mDa Precursor charge2-3 Validation settings Validated hits8 Confidence95% Lowest confidence of validated results100% FDR1 FNR1

x y2y2 y1y1 y4y4 y5y5 y7y7 y8y8 m/z Intensity, cps y 12 GVLM P I L C*PE T F G G x m/z Intensity. cps y2y2 y1y1 y4y4 y5y5 y7y7 y8y8 y9y9 y 5’ y 7’ y 6’ GVLB P I L CPE T F G G GVLM P I L SeCPE T F G G y7y7 y 5’ y 7’ y 6’ m/z Intensity, cps x (‘) Figure S 1. The MS-MS spectra and the identification details of the peptide GILGVLMPGCPETF and its selenium analogue. While the selenopeptide was identified by the search engines as a Sec containing peptide, the manual checking of the MS-MS spectra revealed the absence of Sec containing fragments (y5’, y6’, y7’). In the peptide sequence C* corresponds to carbamydomethyl- cysteine, B denotes to selenomethionine and Sec represents selenocysteine.

m/z Intensity, cps x BSK MB BSK BM MSK BB y1y1 y2y2 y3y3 y4y4 y 2’ y 3’ y 4’ y 4’’ y 2’’ 0 0, x10 4 m/z Intensity, cps MSK BM MSK MB BSK MM y1y1 y3y3 y4y4 y 2’’ y 3’ y 3’’ y 4’ y 4’’ b2b2 y2y2 y 2’ y 2’’ Figure S 2. MS-MS spectra and details of de novo sequencing of selenopeptides. x ,7 1, m/z Intensity, cps MSK MM y1y1 y2y2 y3y3 y4y4

m/z Intensity, cps x y1y1 y2y2 y3y3 y4y4 SFB E GSR S y5y5 y6y6 x , m/z Intensity, cps y1y1 y2y2 y3y3 y4y4 y5y5 y6y6 GKN F CAM V R y7y7 y8y8 x ,2 2, m/z Intensity, cps y1y1 y2y2 y3y3 y4y4 y5y5 y6y6 GKN F CAB V R y7y7 y8y8 x , m/z Intensity, cps y1y1 y2y2 y3y3 y4y4 SFM E GSR S y5y5 y6y6 y7y7

MGM B ENP A E S R BGM M ENP A E S R MGB M ENP A E S R x m/z Intensity, cps y1y1 y2y2 y3y3 y5y5 y6y6 y7y7 y8y8 y 10 y4y4 y 8’ y 10’’ y 9’’ y9y9 y 9’ y 10’ x m/z Intensity, cps ENAM M IY P R A R y1y1 y2y2 y3y3 y4y4 y5y5 y6y6 y7y7 y8y8 y9y9 y 10 m/z Intensity, cps x ENAB M IY P R A R y1y1 y2y2 y3y3 y4y4 y5y5 y6y6 y7y7 y8y8 y9y9 y 10 x m/z Intensity, cps y1y1 y2y2 y4y4 y5y5 y6y6 y7y7 y8y8 MGM M ENP A E S R y9y9 y 10