Cinnamomin, a type II ribosome-inactivating protein, is a storage protein in the seed of the camphor tree (Cinnamomum camphora)

Abstract

Cinnamomin is a novel type II ribosome-inactivating protein (RIP) isolated in our laboratory from the seed of the camphor tree (Cinnamomum camphora). In this paper the physiological role it plays in the plant cell was studied. Northern and Western blotting revealed that cinnamomin was expressed specifically in cotyledons. It accumulated in large amounts simultaneously with other proteins at the post-stages of seed development. Cinnamomin degraded rapidly during the early stages of seed germination. Endopeptidase was proved to play an important role in the degradation of cinnamomin. Western blotting of total INTRODUCTIONPlant ribosome-inactivating proteins (RIPs) are a group of toxic proteins that act on eukaryotic and prokaryotic ribosomes. The molecular mechanism of action of RNA N-glycosidase is to remove a specific adenine from a highly conserved loop (' sarcin\ ricin domain ') in the largest ribosomal RNA that is responsible for the interaction of both eukaryotic and prokaryotic elongation factors with the ribosome, thereby inhibiting protein synthesis [1,2]. RIPs are classified into three types based on their primary structure. Type I RIP consists of a single, intact polypeptide of about 30 kDa which, in some cases, is processed proteolytically into two shorter polypeptides held together by non-covalent interactions. Type II RIP is composed of an N-terminal domain comparable with type I RIP linked by a disulphide bridge to a C-terminal domain that has carbohydrate-binding activity. Type III RIP consists of a type I RIP-like N-terminal domain and a C-terminal domain of unknown function [3].Many studies have been performed on the applications of RIPs in drug development and crop-plant biotechnology due to their toxicity to viruses, tumour cells, insects and plant fungal pathogens [4][5][6]. RIPs have also been used as a powerful probe to study the structure of ribosomes [7]. However, the physiological function that RIPs play in the plant cell is unclear. Previous studies revealed that many RIPs are involved in defence mechanisms in plant cells [4][5][6] and terminate protein synthesis under appropriate physiological conditions and thus are involved in metabolic regulation [8,9]. In addition, some RIPs accumulate in non-reproductive tissues, such as cotyledon, bark and root. Some researchers have proposed that RIP might play a role as a storage protein in these tissues [4,5,10,11]. However, there has been no conclusive evidence to support the storage role of RIP to date.Cinnamomin is a novel type II RIP isolated in our laboratory from the seeds of the camphor tree (Cinnamomum camphora). Its enzymic mechanism, structure and applications have been investigated intensively [12][13][14], but the role it plays in the seed cell of Abbreviations used : DAF ; days after flowering ; DAI ; days after imbibition ; RIP, ribosome-inactivating protein. 1 To whom correspondence should be addressed (e-mail liuwy!sunm.shcnc.ac.cn).proteins from the protein body with antibodies against cinnamomin demonstrated that it only exist...

Purification and characterization of Moschatin, a novel type I ribosome-inactivating protein from the mature seeds of pumpkin (Cucurbita moschata), and preparation of its immunotoxin against human melanoma cells

“…This result may suggest the alternative clinical use of the immunotoxins, so as to reduce immunologic rejection against its toxin moiety. Some RIPs exist abundantly in plant seeds and may play roles as storage proteins [23] for their development, and some of them showed antifungal activities. The possible antifungal activity of Moschatin was also investigated, using eight species of harmful agricultural fungi that were often used in antifungal test (Pellicularia sasakii Ito, Alternaria alternate (Fries) Keissler, Phytophthora boehneriae, Fusarium graminearum Schw, Fusarium moniliforme, Verticillum dahliae, Pellicularia sasakoo Ito, Fusarium oxysporum of Cucumis melo L.).…”

Toxicity of two type II ribosome‐inactivating proteins (cinnamomin and ricin) to domestic silkworm larvae

“…The control for digestion assay was carried out by using distilled water instead of midgut liquid; other conditions are identical. Determination of the undigested cinnamomin by ELISA was carried out as described by Liu et al (2002). The undigested ricin was determined by 12% SDS-PAGE according to the method of Lammeli (1970).…”

Differential expression of ribosome‐inactivating protein genes during somatic embryogenesis in spinach (Spinacia oleracea)

“…However, the expression of some RIP genes is developmentally regulated during the seed and plant development. Cinnamomin, a type-2 RIP identified in camphor (Cinnamomum camphora) (Ling et al 1995, Yang et al 2002, is synthesized in cotyledons and rapidly degraded during germination (Liu et al 2002) and hence has been suggested to be a seed storage protein. Pokeweed (Phytolacca americana) produces three paralogous RIPs.…”