Ribosome-Inactivating Proteins of Bougainvillea glabra Uncovered Polymorphism and Active Site Divergence.

Yihua Lin,Liting Xu,Yijun Liu,Yanyan Li,Hantao Zhou,Xiaobin Wu,Hongmei Zhu

doi:10.3390/toxins13050331

Abstract

Ribosome-inactivating proteins (RIPs) are toxic proteins that can inhibit protein synthesis. RIPs purified from Bougainvillea have low nonspecific toxicity, showing promise for processing applications in the agricultural and medical fields. However, systematic research on the polymorphism of Bougainvillea RIPs is lacking, and it is worth exploring whether different isoforms differ in their active characteristics. The transcriptional and translational expression of type I RIPs in Bougainvillea glabra leaves was investigated in this study. Seven RIPs exhibited seasonal variation at both the mRNA and protein levels. The isoforms BI4 and BI6 showed the highest transcriptional expression in both the summer and autumn samples. Interestingly, BI6 was not detected in the protein level in any of the samples. However, the bioinformatics analysis showed that RIPs derived from the same species were gathered in a different cluster, and that the active sites changed among the isoforms during evolution. The significant discrepancy in Bougainvillea RIPs mainly locates at both termini of the amino acid sequence, particularly at the C terminus. Post-translational modifications may also exist in Bougainvillea RIPs. It is concluded that the reason for the polymorphism of Bougainvillea RIPs may be that these proteins are encoded by multiple genes due to genetic processes such as gene duplication and mutation. According to the results of sequence analysis, the possible functional differences of B. glabra RIP isoforms are discussed with regard to the observed discrepancy in both active sites and structures.

Highlights

Ribosome-inactivating proteins (RIPs) are widely expressed in eukaryotes, including plants, fungi, and algae [1,2], and they can be divided into three types according to differences in structure [3]
The seven sequences of the fulllength bouganin gene were submitted to the National Center of Biotechnology Information. These data show that the RIPs cloned from Bougainvillea glabra exhibited polymorphism in the nucleotide sequence, especially at the 30 end
It was previously shown that the expression of each isoform is affected by a cis-acting element that combines with the transcription factor under jasmonic acid stress [17]

Summary

Introduction

Ribosome-inactivating proteins (RIPs) are widely expressed in eukaryotes, including plants, fungi, and algae [1,2], and they can be divided into three types according to differences in structure [3]. GAGA tetraloop of the major rRNA, leading to ribosome inactivation, preventing the translation process of protein synthesis and promoting cell apoptosis [2,6]. The heterologously expressed RIPs in tobacco plants result in enhanced resistance to Spodoptera exigua with low toxicity to the plant cells [9]. Based on these research facts, RIPs have been shown to confer broad-spectrum resistance to a variety of plant diseases and insect pests, especially in the agricultural field [9,10,11]. A formulation of RIPs combined with antibodies was used to treat cancer, indicating that RIPs have anticancer activity and potential promising applications in the cancer medicine field [5,12,13,14]

Methods

Results

Conclusion