Small Post‐Translationally Modified Peptides – The Making Off

Abstract

Peptide hormones are an emerging new class of signalling molecules in plants, the importance of which has long been underestimated. One important class of peptides is the ‘small post‐translationally modified peptides’ (SPMPs), which require proteolytic processing as an essential step for maturation. SPMPs are derived from pre‐pro‐proteins that consist of 70 to 110 amino acids and harbour the mature peptides at, or close to their C‐termini. All SPMPs are subject to further post‐translational modifications during passage through the secretory pathway, including tyrosine sulphation and/or proline hydroxylation, which may be followed by O‐glycosylation. Despite the prevalence of hydroxyproline (Hyp) in SPMPs, the corresponding enzymes responsible for this post‐translational proline hydroxylation have not been identified, and it is unclear how the specificity of the proline targeted for hydroxylation is achieved. In this article, the current knowledge about the processing, biogenesis, compartmentalization, and post‐translational modifications of SPMPs will be discussed and analysed, and the open questions about the biogenesis of SPMPs will be pointed out.