A snapshot of the Physcomitrella N-terminome reveals N-terminal methylation of organellar proteins

Abstract

Post- or co-translational N-terminal modifications of proteins influence their half-life as well as mediating protein sorting to organelles via cleavable N-terminal sequences that are recognized by the respective translocation machinery. Here, we provide an overview on the current modification state of the N-termini of over 4500 proteins from the model moss Physcomitrella (Physcomitrium patens) using a compilation of 24 N-terminomics datasets. Our data reveal distinct proteoforms and modification states and confirm predicted targeting peptide cleavage sites of 1144 proteins localized to plastids and the thylakoid lumen, to mitochondria, and to the secretory pathway. Additionally, we uncover extended N-terminal methylation of mitochondrial proteins. Moreover, we identified PpNTM1 (P. patens alpha N-terminal protein methyltransferase 1) as a candidate for protein methylation in plastids, mitochondria and the cytosol. These data can now be used to optimize computational targeting predictors, for customized protein fusions and their targeted localization in biotechnology, and offer novel insights into potential dual targeting of proteins. Key messageAnalysis of the N-terminome of Physcomitrella reveals N-terminal monomethylation of nuclear encoded, mitochondria-localized proteins. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=70 SRC="FIGDIR/small/598444v3_ufig1.gif" ALT="Figure 1"> View larger version (17K): org.highwire.dtl.DTLVardef@1f31702org.highwire.dtl.DTLVardef@6b9ce6org.highwire.dtl.DTLVardef@109c041org.highwire.dtl.DTLVardef@12cf83e_HPS_FORMAT_FIGEXP M_FIG C_FIG