Structural studies of the glycopeptides of B-chain of cinnamomin - a type II ribosome-inactivating protein by nuclear magnetic resonance

Cinnamomin is a plant type II ribosome-inactivating protein (RIP) isolated from the seeds of Cinnamomum camphora. It consists of two nonidentical poly peptide chains (A- and B-chain) held together through one disulfide linkage . Its A- and B-chain contain 0.3% and 3.9% sugars respectively. The B-chain of cinnamomin was digested by pronase E and then the liberated glycopeptid es were separated from non-glycopeptides by gel filtration chromatography o n a Bio-Gel P-4 column. Three crude glycopeptides were obtained by continui ng chromatography over anion-exchange resin (AG1-X2) in the buffer of 2% py ridine-acetic acid (pH 8.3) with a polygradient elution system. Through fur ther purification by the gel filtration chromatography and HPLC, three majo r glycopeptides, GP1, GP2 and GP3 were obtained. Mainly by two-dimensional Nuclear Magnetic Resonance (NMR) including TOCSY, DQF-COSY, NOESY, HMQC and HMBC, their primary structures were analyzed as: Man alpha1,3Man alpha1,6( Man alpha1,3)(Xyl beta1,2)Man beta1,4GlcNAc beta1,4GlcNAc beta1-(Gly-)Asn-A sn-Thr(GP1), Man alpha1,6(Man alpha1,3)(Xyl beta1,2)Man beta1,4GlcNAc beta1 ,4(Fuc alpha1,3)GlcNAc beta1-Asn-Ala-Thr(GP2),Man alpha1,6(Man alpha1,3)Man alpha1,6(Man alpha1,2 Man alpha1,3)Man beta1,4GlcNAc beta1,4GlcNAc beta1-( Ala-)Asn-Gly-Thr(GP3).