Functional characterization of an unknown soybean intrinsically disordered protein in vitro and in Escherichia coli

Intrinsically disordered proteins (IDPs) possess a wide range of biological function in all organisms, however the specific functions of most IDPs are still unknown. Soybean LOC protein, LOC for short, is a heat-stable protein, which is more abundant in the stress-resistant radicles. Sequence alignment and phylogenetic analysis showed that LOC is a functionally unknown protein and conserved in Fabaceae. LOC, being enriched in most disorderpromoting residues and depleted in most order-promoting residues, was predicted to contain high levels of intrinsic disorder by several commonly used computational tools. However, it was also predicted to contain two disorder-based protein-protein binding sites and two short a-helical segments. The circular dichroism spectroscopic analysis showed that this protein is mostly disordered in water, but can form more a-helical structure in the presence of SDS and TFE. Functional in vitro studies showed that the LOC protein is able to prevent lactate dehydrogenase inactivation by freeze-thaw at a molar ratio of 10:1. Furthermore, in vivo analyses revealed the survival rate of Escherichia coil over-expressing LOC protein under the conditions of osmotic stress was noticeably increased in comparison with the control. These observations suggest that the intrinsically disordered protein LOC might serve as a chaperone and/or cell protector. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The soybean LOC protein is a heat-stable protein with unknown function, conserved in Fabaceae. It is predicted to contain high levels of intrinsic disorder, but also has disorder-based protein-protein binding sites and short a-helical segments. The protein can prevent lactate dehydrogenase inactivation and increase survival under osmotic stress, suggesting a potential chaperone or cell protector role.