Proline Hydroxylation in Cell Wall Proteins: Is It Yet Possible to Define Rules?

Abstract

Cell wall proteins (CWPs) play critical and dynamic roles in plant cell walls by contributing to developmental processes and response to environmental cues. Since the CWPs go through the secretion pathway, most of them undergo post-translational modifications (PTMs) which can modify their biological activity. Glycosylation is one of the major PTMs of CWPs and refers to N-glycosylation, O-glycosylation and glypiation. Each of these PTMs occurs in different amino acid contexts which are not all well defined. This article deals with the hydroxylation of Pro residues which is a prerequisite for O-glycosylation of CWPs on hydroxyproline (Hyp) residues. The location of Hyp residues is well described in several structural CWPs, but yet rarely described in other CWPs. In this article, it is studied in detail in five Arabidopsis thaliana proteins using mass spectrometry data: one of them (At4g38770, AtPRP4) is a structural CWP containing 32.5% of Pro residues arranged in typical motifs, the others are either rich (27–28%, At1g31580 and At2g10940) or poor (6–8%, At1g09750 and At3g08030) in Pro residues. The known rules of Pro hydroxylation allowed a good prediction of Hyp location in AtPRP4. However, they could not be applied to the other proteins whatever their Pro content. In addition, variability of the Pro hydroxylation patterns was observed within some amino acid motifs in all the proteins and new patterns of Pro hydroxylation are described. Altogether, this work shows that Hyp residues are present in more protein families than initially described, and that Pro hydroxylation patterns could be different in each of them. This work paves the way for completing the existing Pro hydroxylation code.

The Arabidopsis Proteins AtNHR2A and AtNHR2B Are Multi-Functional Proteins Integrating Plant Immunity With Other Biological Processes

“…AtNHR2B also interacted with a putative polygalacturonase (Duan et al, 2016). Other AtNHR2A interactors localized to the extracellular space and functioning in cell wall biosynthesis included the extensin AtEXT2 (Liepman et al, 2010), and a proline-rich glycoprotein (Durufle et al, 2017). However, we did not find experimental evidence that these two proteins participate in plant immunity.…”

Identification of Hydroxyproline-Containing Proteins and Hydroxylation of Proline Residues in Rice

“…Hydroxyproline residues in the HCPs may form O-linked glycosylation modification ( Showalter et al., 2010 ; Hijazi et al., 2012 ; Showalter et al., 2016 ) and play roles in plants ( Hirsilä et al., 2003 ; Duruflé et al., 2017 ). AGPs containing Hyps are considered to have AG-type glycomodules ( Ma et al., 2017 ).…”

Plant Cell Wall Proteomics: A Focus on Monocot Species, Brachypodium distachyon, Saccharum spp. and Oryza sativa

“…The constitution and structure of the CWPs collection are diverse due to the developmental stage, organ, tissue and species of the analyzed material; thus, it is possible to make a comparison among these different treatments and relate them physiologically [7]. Initial studies have been made on Arabidopsis thaliana [11,16,17,18,19,20,21,22]. Since then, CWPs from several other species have been identified by mass spectrometry.…”

“…Since then, CWPs from several other species have been identified by mass spectrometry. In A. thaliana , about one half of the predicted existing CWPs were identified, being the most studied plant at present, with 935 proteins already identified [11,16,17,18,19,20,21,22]. In addition to providing an overview of proteins present in a biological context, the identification of CWPs in A. thaliana enabled the selection of candidates to have their structure and function further investigated.…”