Mono-PEGylation of ribonuclease A: High PEGylation efficiency by thiolation with small molecular weight reagent

PEGylation can improve the therapeutic potential of ribonuclease A (RNase A), a cancer chemotherapeutic agent. However, the common PEGylation that targets at the ?-amino groups of proteins can lead to imprecise control of the stoichiometry of the protein-PEG conjugate (i.e., mono-, di- and multi-PEGylated protein). To prepare a PEGylated therapeutic protein, it is desirable that the protein is mono-PEGylated for industrial production, convenient purification and analytical characterization. Here, N-hydroxysuccinimide esters of S-acetylthioacetic acid (SATA) and 2-iminothiolane (IT) were used to introduce thiol groups on RNase A, followed by maleimide chemistry based PEGylation of the thiolated RNase A. Interestingly, the yield of mono-PEGylated RNase A was higher than 60%, and di- or multi-PEGylated RNase A were absent in the PEGylated product. Presumably, the limited number and low solvent accessibility of the introduced thiol group favored mono-PEGylation of RNase A. As compared to the unmodified RNase A, the mono-PEGylated RNase A showed slightly decreased enzymatic activity, increased anti-proliferative ability and unchanged structural properties. Our study is expected to control the PEGylation process and optimize the industrial pharmaceutical production of PEGylated proteins.     

Ectopic expression of the spike protein of Rice Ragged Stunt Oryzavirus in transgenic rice plants inhibits transmission of the virus to insects

Rice ragged stunt oryzavirus (RRSV) replicates in both its insect vector, Nilaparvata lugens, and its plant host, rice, and has a complex multi-component particle bearing spikes on its outer surface. Transgenic rice lines expressing the 39 kDa spike protein showed good resistance to infection by RRSV. Furthermore, N. lugens fed on these plants prior to feeding on RRSV-infected plants were significantly protected against RRSV infection. The viral titre in insects initially fed on transgenic plants and then on RRSV-infected plants was inversely proportional to the levels of the 39 kDa protein expressed in the transgenic plants. This suggests that the 39 kDa protein interferes with the interaction between the intact virus particles and insect cell receptors and that the spike protein of RRSV contributes to vector specificity. This approach would probably be a more environment-friendly and sustainable method of virus control than by actual eradication of insect vectors.