Mannose Analog 1-Deoxymannojirimycin Inhibits the Golgi-Mediated Processing of Bean Storage Glycoproteins

Abstract

The asparagine-linked oligosaccharide chains of glycoproteins can be processed to form a wide variety of structures. The Golgi complex is the main compartment involved in this processing. In mammalian cells the first enzyme acting along the Golgi processing pathway is mannosidase 1, whose action is a prerequisite for any further processing and which is inhibited by the mannose analog 1-deoxymannojirimycin (dMM). To have insights into the processing pathway in plant cells, we have studied the In vivo effect of dMM on the processing of the bean (Phaseolus vulgads) storage proteins phaseolin and phytohemagglutinin, two well characterized plant glycoproteins. Cotyledons obtained from developing seeds were labeled with radioactive leucine, glucosamine, or fucose in the presence or absence of dMM. Treatment with dMM fully inhibited the acquisition of resistance to endo-#-N-acetylglucosaminidase H by phaseolin and phytohemagglutinin and the incorporation of fucose into protein. Furthermore, the apparent molecular weight of the polypeptides of phaseolin and phytohemagglutinin synthesized in dMM-treated cotyledons was consistent with the exclusive presence of oligommanose oligosaccharide chains which had not been processed in the Golgi complex. The inhibition of processing did not prevent exit from the Golgi complex, and most probably the storage proteins were correcty targeted to the protein bodies as indicated by the posttranslatonal polypeptide cleavage of phaseolin. These resuits indicate that the action of a mannosidase is the first obligatory step of Golgi-mediated processing also in a plant cell and, together with data obtained in other laboratories on the In vitro specificity of glycosidases and glycosyltransferases present in the Golgi complex of plant cells, support the hypothesis that the key early reactions in Golgi-mediated processing are similar if not identical in plants and mammals.

Bean homologs of the mammalian glucose‐regulated proteins: induction by tunicamycin and interaction with newly synthesized seed storage proteins in the endoplasmic reticulum

“…This is consistent with the idea that GRPs are induced by the presence of unfolded proteins in the ER, since negative processes occurring in the Golgi complex or later are not likely to be circumvented by the action of proteins which reside in an earlier compartment of the secretory pathway. As already observed in mammalian cells, the synthesis of bean GRPs is not significantly affected by treatment with dMM, an inhibitor of both mammalian (Fuhrmann et a/., 1984) and plant (Vitale et a/., 1989a) Golgi-mediated processing. We had previously shown that dMM fully inhibits processing of the carbohydrate chains of PHSL and PHA (Vitale et a/., 1989a).…”

“…As already observed in mammalian cells, the synthesis of bean GRPs is not significantly affected by treatment with dMM, an inhibitor of both mammalian (Fuhrmann et a/., 1984) and plant (Vitale et a/., 1989a) Golgi-mediated processing. We had previously shown that dMM fully inhibits processing of the carbohydrate chains of PHSL and PHA (Vitale et a/., 1989a). This further supports our conclusion that bean GRPs are the functional homologs of mammalian GRPs, and also complements the cell fractionation experiments in locating these proteins as residents of the ER.…”

Environmental factors and intrinsic processes affecting habitat use of European ground squirrels (Spermophilus citellus): putting science into conservation practice

“…Soil properties are major factors that govern ecosystem processes (Chapin, Matson, and Mooney 2002) and are of paramount importance for ground dwelling animals. The characteristics of soil within the habitat could be the main determinants of habitat use (Parer 1985;Vitale, Zoppe, and Bollini 1989;McCarley 1966;Scharff and Burda 1998).For burrowing mammals, the physical property of the soil determines basically if digging is feasible. However, soil properties and morphology are also influenced by several factors e.g.…”

“…Oryctolagus cuniculus which digs its burrow system under the roots of Juniperus communis (Parer 1985;Altbäcker, Nyéki, and Kertész 1997)). These shelters and resting places are more durable than burrows in the seahore sand dunes (Vitale, Zoppe, and Bollini 1989). Another pictorial example of soil disturbance by vertebrate animals (biopedturbation) is the burrows and mounds of many subterranean, fossorial, and semi-fossorial mammals.…”