Ricin A chain insertion into endoplasmic reticulum membranes is triggered by a temperature increase to 37 degrees C

After endocytic uptake by mammalian cells, the heterodimeric plant toxin ricin is transported to the endoplasmic reticulum (ER), where the ricin A chain (RTA) must cross the ER membrane to reach its ribosomal substrates. Here, using gel filtration chromatography, sedimentation, fluorescence, fluorescence resonance energy transfer, and circular dichroism, we show that both fluorescently labeled and unlabeled RTA bind both to ER microsomal membranes and to negatively charged liposomes. The binding of RTA to the membrane at 0-30 degrees C exposes certain RTA residues to the nonpolar lipid core of the bilayer with little change in the secondary structure of the protein. However, major structural rearrangements in RTA occur when the temperature is increased. At 37 degrees C, membrane-bound toxin loses some of its helical content, and its C terminus moves closer to the membrane surface where it inserts into the bilayer. RTA is then stably bound to the membrane because it is nonextractable with carbonate. The sharp temperature dependence of the structural changes does not coincide with a lipid phase change because little change in fluorescence-detected membrane mobility occurred between 30 and 37 degrees C. Instead, the structural rearrangements may precede or initiate toxin retrotranslocation through the ER membrane to the cytosol. The sharp temperature dependence of these changes in RTA further suggests that they occur optimally in mammalian targets of the plant toxin

Disability and health-related quality of life in patients undergoing spinal fusion: a comparison with a general population sample.

Background. The aim of the present study was to compare one-year-follow-up data on disability and health-related quality of life (HRQoL) between spinal fusion patients and age- and sex-matched general population. Methods. The data on fusion patients were collected prospectively using a spinal fusion data base in two Finnish hospitals. A general population sample matched for age, sex and residential area was drawn from the Finnish Population Register. All participants completed a questionnaire and the main outcome measures were the Oswestry Disability Index (ODI) and the Short Form-36 questionnaire (SF-36). Results. Altogether 252 (69% females) fusion patients and 682 (67% females) population sample subjects participated in the study. In general population the mean ODI was 15 (SD 17) in females and 9 (SD 13) in males. The corresponding preoperative ODI values were 47 (SD16) and 40 (SD 15) and one year follow-up values 22 (SD 17) and 23 (SD 20). In both sexes the ODI decreased significantly after surgery but remained higher than in the general population, p < 0.001. The physical component summary score (PCS) of the SF-36 was lower in the patients than general population sample both preoperatively and at one-year follow-up (p < 0.001). The mental component summary score (MCS) was lower preoperatively (p < 0.001), but reached the general population level after one year in both men (p = 0.42) and women (p = 0.61). Conclusions. Disability and HRQoL improved significantly after spinal fusion surgery during a one- year follow-up. However, the patients did not reach the level of the general population in the ODI or in the physical component of HRQoL at that time, although in the mental component the difference disappeared.peerReviewe