title: Topological transformation of liposomes by a membrane-affecting domain of recombinant human erythropoietin.
abstract: Recombinant human erythropoietin (rh-Epo) is well accepted as a hematopoietic drug, but many other pleiotropic properties are currently under investigation. Rh-Epo-induced receptor-mediated signal transductions are accompanied with membrane dynamic processes, which facilitate the activation of individual pathways. However, its direct effect on membrane dynamics is still unknown. In the present study, we have proven the capability of rh-Epo to associate to and transform artificial lipid membranes. Association studies using neutral, negatively, and positively charged liposomes with the native as well as modified rh-Epo were performed and analyzed by transmission electron microscopy and differential scanning calorimetry. By these studies, we demonstrated that rh-Epo has the capability to transform negatively charged unilamellar vesicles into so-called disc-like micelles. Rh-Epo association to the negatively charged head groups via lysine and arginine initiates this transformation. At physiological temperatures, conformational changes within the rh-Epo structure expose a defined amino-acid sequence, which is able to induce the formation of discoid membrane structures. Enzymatic digestion, analysis, and isolation of related peptides by rp-HPLC and characterization by MS/MS enabled the identification of the membrane-affecting domain of rh-Epo (MAD-E) that represents the exposed helix B of rh-Epo. Finally, association studies performed with these peptides confirmed that the MAD-E is responsible for the formation of disc-like micelles. Since this helix B of rh-Epo has recently been supposed to be involved in the activation of neuroprotective pathways, we believe that the membrane-transforming capacity of rh-Epo participates in the proliferative activity of rh-Epo.
authors.affiliation: Department of Biotechnology, University of Natural Resources and Applied Life Sciences, Vienna, Austria. stefanie.strobach@boku.ac.at
authors.forename: Stefanie
authors.initials: S
authors.lastname: Strobach
authors.forename: Renate
authors.initials: R
authors.lastname: Kunert
authors.forename: Johannes
authors.initials: J
authors.lastname: Stadlmann
authors.forename: Paul
authors.initials: P
authors.lastname: Messner
authors.forename: Eva
authors.initials: E
authors.lastname: Sevcsik
authors.forename: Gabriele
authors.initials: G
authors.lastname: Lhota
authors.forename: Hermann
authors.initials: H
authors.lastname: Katinger
authors.forename: Karola
authors.initials: K
authors.lastname: Vorauer-Uhl
mesh_terms: D000595:Amino Acid Sequence; D002152:Calorimetry, Differential Scanning; D022082:Cellular Structures / Q000378:metabolism; D004921:Erythropoietin / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology*; D006801:Humans; D008081:Liposomes / Q000737:chemistry*; D008566:Membranes / Q000378:metabolism; D017433:Protein Structure, Secondary / Q000235:genetics; D011994:Recombinant Proteins; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D014162:Transfection
chemical_list: D008081:Liposomes; D011994:Recombinant Proteins; D004921:Erythropoietin