Dehydrin client proteins identified using phage display affinity selected libraries processed with Paired-End PhAge Sequencing (PEPA-Seq).

The LATE EMBRYOGENESIS ABUNDANT PROTEINs (LEAPs) are a class of noncatalytic, intrinsically disordered proteins with a malleable structure. Some LEAPs exhibit a protein and/or membrane binding capacity and LEAP binding to various targets has been positively correlated with abiotic stress tolerance. Regarding the LEAPs' presumptive role in protein protection, identifying client proteins (CtPs) to which LEAPs bind is one practicable means of revealing the mechanism by which they exert their function. To this end, we used phage display affinity selection to screen libraries derived from Arabidopsis thaliana seed mRNA with recombinant orthologous LEAPs from Arabidopsis and soybean (Glycine max). Subsequent high throughput sequencing of DNA from affinity-purified phage was performed to characterize the entire sub-population of phage retained by each LEAP orthologue. This entailed cataloging in-frame fusions, elimination of false positives, and aligning the hits on the CtP scaffold to reveal domains of respective CtPs that bound to orthologous LEAPs. This approach (Paired-end PhAge Sequencing, or PEPA-Seq) revealed a subpopulation of the proteome constituting the CtP repertoire in common between the two DHNs orthologues (LEA14 and GmPm12) compared to BSA (unrelated binding control). The veracity of LEAP:CtP binding for one of the CtPs (LEA14 and GmPM12 self-association) was independently assessed using temperature related intensity change (TRIC) analysis. Moreover, LEAP:CtP interactions for four other CtPs were confirmed in planta using bimolecular fluorescence complementation (BiFC) assays. The results provide insights into the involvement of the DHN Y-segments and K-domains in protein binding.

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