Genome-Wide Characterization of Wholly Disordered Proteins in Arabidopsis

Intrinsically disordered proteins (IDPs) include two types of proteins: one contains partial disordered regions (IDRs), the other is wholly disordered proteins (WDPs). Extensive studies focused on the proteins with IDRs, but less is known about WDPs because of their difficult to form the folded tertiary structure. In this study, we developed a bioinformatics method for screening WDPs more than 50 amino acids in the genome level and found a total of 27 categories including 56 WDPs in Arabidopsis. After comparing with randomly selected 56 structural proteins, we found that WDPs possessed more wide range of theoretical isoelectric point (PI), more negative of Grand Average of Hydropathicity (GRAVY), higher value of Instability Index (II) and lower values of Aliphatic Index (AI). In addition, by calculating the FCR (fraction of charged residue) and NCPR (net charge per residue) values of each WDP, we found twenty WDPs in R1 (FCR < 0.25 & NCPR < 0.25) group, fifteen in R2 (0.25 ≤ FCR ≤ 0.35 & NCPR ≤ 0.35), nineteen in R3 (FCR > 0.35 & NCPR ≤ 0.35), and two in R4 (FCR > 0.35 & NCPR > 0.35). Moreover, the gene expression and protein-protein interaction (PPI) network analysis showed that WDPs perform different biological functions. We also showed that two WDPs, SIS (Salt Induced Serine rich) and RAB18 (a dehydrin family protein) undergo the in vitro liquid-liquid phase separation (LLPS). Therefore, our results provide insight into understanding the biochemical characters and biological functions of WDPs in plants.