Characterization of a pathogenesis-related class 10 protein (PR-10) from Astragalus mongholicus with ribonuclease activity

Abstract

A pathogenesis-related (PR) class 10 protein (designated AmPR-10) was first isolated from the Chinese medicinal material Astragalus mongholicus using a combination of affinity chromatography on Zn-chelate Agarose 4B, ion exchange chromatography on QAE Sephadex A-25 and gel filtration on Sephadex G50. The purified AmPR-10 showed a single band with a molecular mass of 17.2 kDa in SDS-PAGE. The molecular mass of intact AmPR-10 was determined to be 32.8 kDa by gel filtration. Thus, AmPR-10 is a dimeric protein composed of two identical subunits. AmPR-10 was a glycoprotein detected by periodic acid-Schiff (PAS) staining and its neutral carbohydrate content was 13.7%. The carbohydrate was mainly composed of 73.0% (w/w) arabinose, 15.0% (w/w) glucose and 4.8% (w/w) fructose on the basis of high-performance anion exchange chromatography (HPAEC) analysis. Its N-terminal sequence of 15 amino acid residues was determined as GVISFNEETISTVAP, and showed significant sequence homology to some pathogenesis-related (PR) class 10 proteins. This sequence had 80% identity with the PR-10 protein LlPR10.1C from Lupinus luteus (yellow lupine) followed by 73.3% identity with the PR-10 protein PR10.2 from Medicago sativa (alfalfa), suggesting it is a new member of PR-10 proteins. AmPR-10 exhibited ribonuclease (RNase) activity as do some other PR-10 proteins. The optimal pH and temperature for RNase activity were pH 6.0 and 60 °C, respectively. The RNase activity was stable within pH 5.0–11.0. It was stable up to 60 °C at pH 6.0. The purification and characterization of AmPR-10 in this investigation furnish additional data to the relatively scanty literature pertaining to Astragali radix proteins.