Identification of Proteins from Cap-Binding Complexes by Mass Spectrometry During Maize (Zea mays L.) Germination

Abstract

This work describes the identification of components in the Cap-binding complexes in non-germinated and 24-h-imbibed seeds using mass spectrometry. This approach revealed new components particularly present in the non-germinated seed. Among these, two heat shock proteins, HSP101 and HSP70, were detected as well as several proteins involved in carbohydrate metabolism. Between the new components of maize Cap-binding complexes, several proteins contain a motif that identifies them as potential direct interactors with eIF4E or eIF(iso)4E.Together with the major abundance of eIF(iso)4E at this developmental stage, our findings indicate clear differences between the translation initiation complexes that are available for protein synthesis right upon water imibition and those that are present once germination has been completed.

A novel eIF4E-interacting protein that forms non-canonical translation initiation complexes

“…Due to the importance of translation regulation through eIF4E-dependent mechanisms in other eukaryotes, there have been multiple attempts to identify possible eIF4E-dependent translational regulators in plants. These analyses included previous yeast two-hybrid screenings using AteIF(iso)4E as bait and a cDNA library from etiolated seedlings and the identification by mass spectrometry of proteins able to bind to the cap structure from Arabidopsis cell cultures and wheat seeds 15,26,28 . Despite the fact that these assays allowed the identification of different proteins that bind eIF4E isoforms in plants 26,27,29,30 ; the direct role of these proteins in translation has remained mainly elusive.…”

“…More importantly, it has been described that in plants the interaction between the components of the eIF4F and eIF(iso)4F complexes is at the nanomolar to subnanomolar level, which makes unlikely that these complexes readily dissociate once formed 13 . In addition, although different proteins that contain a canonical 4E-BS and bind eIF4E and eIF(iso)4E have been described in Arabidopsis and wheat (such as LOX2, BTF3, CBE1 or EXA1) [26][27][28][29][30] , their direct role in translation has not been proven, leaving the existence of possible analogues or completely new eIF4E translational regulators unexplored.…”

Regulation of Translation by TOR, eIF4E and eIF2α in Plants: Current Knowledge, Challenges and Future Perspectives

“…Besides the lack of plant orthologs for the 4E-BPs and eIF4E-interacting partners, the existence of proteins that regulate eIF4E activity through eIF4E association remains an open question. Different studies reported the identification of proteins bearing the consensus 4E-BM that bind eIF4E and eIFiso4E ( Freire et al, 2000 ; Freire, 2005 ; Lázaro-Mixteco and Dinkova, 2012 ), although their role in translation has yet to be elucidated. Apart from these proteins, an Arabidopsis database search retrieves more than 6900 proteins that contain one or more canonical eIF4E-binding domains (YXXXXLØ) ( Toribio et al, 2016 ), that therefore might bind eIF4E and regulate its function.…”

Decoding the translation initiation mechanism of maize chlorotic mottle virus

“…For example, during seed storage, eIFiso4E is expressed at higher levels than eIF4E, even though eIF4E levels are low in the mature seed, they increase upon germination (Dinkova et al, 2011). During germination and growth stages, almost all eIF4E paralogs and isoforms are active (Dinkova et al, 2000;Dinkova and Sanchez de Jimenez, 1999;Lázaro-Mixteco and Dinkova, 2017;Xu et al, 2017), and this makes sense as the plants'…”

“…The expression levels of eIF4E and eIFiso4E vary depending on the developmental stage of the maize plant (Dinkova and Sánchez de Jiménez, 1999). Although the protein sequence of maize eIF4E has been characterized (Dinkova et al, 2000;Lázaro-Mixteco and Dinkova, 2017;Manjunath et al, 1999), there is no crystal structure of this protein yet. As there was no maize eIF4E at the protein data bank (PDB), homologous protein structures of eIF4E were searched for comparison.…”