Post-translational modifications in secreted peptide hormones in plants

Abstract

More than a dozen secreted peptides are now recognized as important hormones that coordinate and specify cellular functions in plants. Recent evidence has shown that secreted peptide hormones often undergo post-translational modification and proteolytic processing, which are critical for their function. Such 'small post-translationally modified peptide hormones' constitute one of the largest groups of peptide hormones in plants. This short review highlights recent progress in research on post-translationally modified peptide hormones, with particular emphasis on their structural characteristics and modification mechanisms.

Fig. 1

Three distinct biosynthetic pathways of secreted peptide hormones categorized by their structural characteristics. Secreted peptide hormones can be categorized into the following three groups: peptides involving complex post-translational modifications followed by extensive proteolytic processing; peptides involving intramolecular disulfide bond formation followed by proteolytic processing; and peptides involving multiple intramolecular disulfide bonds without proteolytic processing. The first group of peptides are called small post-translationally modified peptides; the latter two groups are defined as cysteine-rich peptides.

Fig. 2

Structural characteristics of primary amino acid sequences of precursor polypeptides that represent small post-translationally modified peptides. Deduced amino acid sequences of (A) PSK, (B) PSY1, (C) CLV3 and CLE2, (D) CEP1 (E) RGF1, and their representative homologs are shown. Domains encoding mature peptides are underlined. Identical amino acid residues are highlighted in black, and similar amino acid residues are highlighted in gray.

Fig. 3

Tyrosine sulfation by tyrosylprotein sulfotransferase (TPST). TPST catalyzes the transfer of sulfate from the sulfate donor 3′-phosphoadenosine-5′-phosphosulfate (PAPS) to the hydroxyl group of a tyrosine residue to form a tyrosine sulfate ester and adenosine 3′, 5′-diphosphate (PAP). R₁ and R₂ represent peptide chains.

Fig. 4

Proposed structure of hydroxyproline-bound triarabinoside. Linear β-1,2-linked triarabinoside is suggested to be a common structure in glycopeptide hormones. R₁ and R₂ represent peptide chains.