Identification of a plant-specific Zn2+-sensitive ribonuclease activity

Arabidopsis ENDO2: its catalytic role and requirement of N-glycosylation for function

The Arabidopsis thaliana At1g68290 gene encoding an endonuclease was isolated and designated ENDO2, which was cloned into a binary vector to overexpress ENDO2 with a C-terminal 6 × His-tag in A. thaliana. Our Arabidopsis transgenic lines harboring 35SP::ENDO2 produced stable active enzyme with high yield. The protein was affinity purified from transgenic plants, and its identity was confirmed by liquid chromatography-mass spectrometry and automatic Edman degradation. ENDO2 enzyme digests RNA, ssDNA, and dsDNA, with a substrate preference for ssDNA and RNA. The activity toward ssDNA (361.7 U/mg) is greater than its dsDNase activity (14.1 U/mg) at neutral pH. ENDO2 effectively cleaves mismatch regions in heteroduplex DNA containing single base pair mismatches or insertion/deletion bases and can be applied to high-throughput detection of single base mutation. Our data also validated that the removal of sugar groups from ENDO2 strongly affects its enzymatic stability and activity.

Identification of S-RNase and peroxidase in petunia nectar

Previous SDS PAGE gel analysis of the floral nectars from petunia and tobacco plants revealed significant differences in the protein patterns. Petunia floral nectar was shown to contain a number of RNase activities by in gel RNase activity assay. To identify these proteins in more detail, the bands with RNase activity were excised from gel and subjected to trypsin digestion followed by LC-MS/MS analysis. This analysis revealed that S-RNases accumulate in nectar from Petunia hybrida, where they should carry out a biological function different from self-pollen rejection. In addition, other proteins were identified by the LC-MS/MS analysis. These proteins include a peroxidase, an endochitinase, and a putative fructokinase. Each of these proteins contained a secretory signal sequence that marked them as potential nectar proteins. We developed RT-PCR assays for each of these five proteins and demonstrated that each of these proteins was expressed in the petunia floral nectary. A discussion of the role of these proteins in antimicrobial activity in nectar is presented.

Ribonucleases of different origins with a wide spectrum of medicinal applications

Ribonucleases (RNases) are a type of nucleases that catalyze the degradation of RNA into smaller components. They exist in a wide range of life forms from prokaryotes to eukaryotes. RNase-controlled RNA degradation is a determining factor in the control of gene expression, maturation and turnover, which are further associated with the progression of cancers and infectious diseases. Over the years, RNases purified from multiple origins have drawn increasing attention from medical scientists due to their remarkable antitumor properties. In this review, we present a brief summary of the representative RNases of fungal, bacterial, plant, and animal origins and outline their potential medicinal value in the treatment of tumor and AIDS. Among them, the most clinically promising RNases are mushroom RNases, Binase and Barnase from bacteria, ginseng RNases, and Onconase from frog (Rana pipiens). Fast developing protein engineering of RNases, which display more potent cytotoxic activity on and greater selectivity for malignant cells, has also aroused the interest of researchers. The multiple anti-cancer mechanisms of RNases are also included. To sum up, these inspiring studies unveil a new perspective for RNases as potential therapeutic agents.