1. A napin-like polypeptide with translation-inhibitory, trypsin-inhibitory, antiproliferative and antibacterial activities from kale seeds
P H K Ngai, T B Ng J Pept Res. 2004 Nov;64(5):202-8. doi: 10.1111/j.1399-3011.2004.00186.x.
A heterodimeric napin-like polypeptide with translation-inhibiting and antibacterial activities has been isolated from kale seeds. The purification procedure entailed ion-exchange chromatography on dielthylaminoethyl (DEAE)-cellulose, affinity chromatography on Affi-gel blue gel, ion-exchange chromatography by fast protein liquid chromatography (FPLC) on Mono S, and gel filtration by FPLC on Superdex 75. The napin-like polypeptide was unadsorbed on DEAE-cellulose but adsorbed on Affi-gel blue gel and Mono S. Its 7-kDa large subunit differs in N-terminal amino acid sequence from the 4-kDa small subunit. The polypeptide inhibited translation in the rabbit reticulocyte lysate system with an IC50 of 37.5 nM. This activity was preserved between pH 5 and pH 11, and between 10 and 40 degrees C. It fell to a low level at pH 3 and pH 13 and at 70 degrees C. Antibacterial activity against Bacillus, Megabacterium, and Pseudomonas species and antiproliferative activity against leukemia L1210 cells were observed. However, the polypeptide did not exert antifungal, ribonuclease, or protease activity.
2. Isolation of a napin-like polypeptide with potent translation-inhibitory activity from Chinese cabbage (Brassica parachinensis cv green-stalked) seeds
Patrick H K Ngai, T B Ng J Pept Sci. 2003 Jul;9(7):442-9. doi: 10.1002/psc.460.
A heterodimeric napin-like polypeptide was isolated from Brassica parachinensis seeds with a procedure involving ion exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue gel, FPLC-ion exchange chromatography on Mono S and FPLC-gel filtration on Superdex 75. The N-terminal sequence of the 5 kDa subunit of the polypeptide (PAGPFRIPKKRKKEE) showed high homology with other 2S storage proteins like napins and albumins. The polypeptide potently inhibited translation in a cell free system with an IC50 of 6.2 nM. The translation-inhibiting activity of the polypeptide was relatively stable in the pH range 6-11 and in the temperature range 10-50 degrees C.
3. A napin-like polypeptide from dwarf Chinese white cabbage seeds with translation-inhibitory, trypsin-inhibitory, and antibacterial activities
P H K Ngai, T B Ng Peptides. 2004 Feb;25(2):171-6. doi: 10.1016/j.peptides.2003.12.012.
Napins are 1:1 disulfide-linked complexes of a smaller (ca. 4kDa) subunit and a larger (ca. 10kDa) subunit. The intent of the present study was to ascertain the production of napin by the seeds of a Brassica species that has not been examined previously, and also to explore new biological activities of the napin. A heterodimeric 11-kDa napin-like polypeptide has been isolated from Chinese white cabbage (Brassica chinensis cv dwarf) seeds with a protocol comprising ion exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue gel, fast protein liquid chromatography (FPLC)-ion exchange chromatography on Mono S and FPLC-gel filtration on Superdex 75. The N-terminal sequence of the 7-kDa subunit manifests striking similarity to napin large chain, albumin and trypsin inhibitor. The N-terminal sequence of the 4-kDa subunit is homologous to napin large chain and an antimicrobial peptide. The napin-like polypeptide inhibited translation in the rabbit reticulocyte system with an IC50 of 18.5nM. This translation-inhibitory activity was stable between pH 4 and 11, and between 10 and 40 degrees C. The polypeptide inhibited trypsin with a higher potency ( IC50 = 8.5 microM) than it inhibited chymotrypsin (IC50 = 220 microM), but was devoid of ribonuclease and antifungal activities. It manifested antibacterial activity against Pseudomonas aeruginosia, Bacillus subtilis, Bacillus cereus, and Bacillus megaterium. The results revealed that the napin-like polypeptide from Chinese white cabbage seeds exhibited some potentially exploitable activities.
