Chemical and Enzymatic Synthesis of Sialylated Glycoforms of Human Erythropoietin.

Recombinant human erythropoietin (EPO) is the main therapeutic glycoprotein for the treatment of anemia in cancer and kidney patients. The in-vivo activity of EPO is carbohydrate-dependent with the number of sialic acid residues regulating its circulatory half-life. EPO carries three N-glycans and thus obtaining pure glycoforms provides a major challenge. We have developed a robust and reproducible chemoenzymatic approach to glycoforms of EPO with and without sialic acids. EPO was assembled by sequential native chemical ligation of two peptide and three glycopeptide segments. The glycopeptides were obtained by pseudoproline-assisted Lansbury aspartylation. Enzymatic introduction of the sialic acids was readily accomplished at the level of the glycopeptide segments but even more efficiently on the refolded glycoprotein. Biological recognition of the synthetic EPOs was shown by formation of 1:1 complexes with recombinant EPO receptor.

Natural Glycoforms of Human Interleukin 6 Show Atypical Plasma Clearance.

A library of glycoforms of human interleukin 6 (IL-6) comprising complex and mannosidic N-glycans was generated by semisynthesis. The three segments were connected by sequential native chemical ligation followed by two-step refolding. The central glycopeptide segments were assembled by pseudoproline-assisted Lansbury aspartylation and subsequent enzymatic elongation of complex N-glycans. Nine IL-6 glycoforms were synthesized, seven of which were evaluated for in vivo plasma clearance in rats and compared to non-glycosylated recombinant IL-6 from E. coli. Each IL-6 glycoform was tested in three animals and reproducibly showed individual serum clearances depending on the structure of the N-glycan. The clearance rates were atypical, since the 2,6-sialylated glycoforms of IL-6 cleared faster than the corresponding asialo IL-6 with terminal galactoses. Compared to non-glycosylated IL-6 the plasma clearance of IL-6 glycoforms was delayed in the presence of larger and multibranched N-glycans in most cases.

Synthetic Glycoforms Reveal Carbohydrate-Dependent Bioactivity of Human Saposin†D.

The main glycoforms of the hydrophobic lysosomal glycoprotein saposin D (SapD) were synthesized by native chemical ligation. An approach for the challenging solid-phase synthesis of the fragments was developed. Three SapD glycoforms were obtained following a general and robust refolding and purification protocol. A crystal structure of one glycoform confirmed its native structure and disulfide pattern. Functional assays revealed that the lipid-binding properties of three SapD glycoforms are highly affected by the single sugar moiety of SapD showing a dependency of the size and the type of N-glycan.

Investigating the efficiency of a bio-inspired insect repellent surface structure.

Most insects with smooth or hairy adhesive pads have very little problems in attaching to smooth substrates. A careful selection of surface roughness, however, can effectively limit the contact area of the adhesive organs with the surface. In comparison to conventional toxin-based insect repelling methods, biologically inspired micro- and nanostructured insect repellent surface structures, thus, offer a great potential to effective and environmentally-friendly control insect pests. We here present a simple experimental approach to qualitatively and quantitatively analyse the efficiency of a micro- and nanorough surface structure. Nauphoeta cinerea and Gastrophysa viridula as model organisms for insects with smooth and hairy adhesive pads, respectively, were placed in an enclosed environment. The escape movements of freely running insects over either the repellent or a control surfaces were counted and analyzed in detail. The tested surface structures were able to significantly reduce the escape of cockroaches with smooth adhesive pads by 44.1%. Interestingly, the data indicates that N. cinerea might use mechanical cues from the antenna to discriminate between surfaces before making contact with the adhesive pads. G. viridula with hairy adhesive pads were not significantly affected by the surface structure. By carefully adjusting 'critical' surface topography parameters relevant for insect adhesion, more efficient and selective repellent surfaces might be achieved. Such nanostructure-based insect repellent surfaces could also help to utilize recruitment behavior of certain insect species and might present a novel approach to effectively control insect pests.

Myocardial adaptation of energy metabolism to elevated preload depends on calcineurin activity : a proteomic approach.

Chronic hemodynamic overload on the heart results in pathological myocardial hypertrophy, eventually followed by heart failure. Phosphatase calcineurin is a crucial mediator of this response. Little is known, however, about the role of calcineurin in response to acute alterations in loading conditions of the heart, where it could be mediating beneficial adaptational processes. We therefore analyzed proteome changes following a short-term increase in preload in rabbit myocardium in the absence or presence of the calcineurin inhibitor cyclosporine A. Rabbit right ventricular isolated papillary muscles were cultivated in a muscle chamber system under physiological conditions and remained either completely unloaded or were stretched to a preload of 3 mN/mm(2), while performing isotonic contractions (zero afterload). After 6 h, proteome changes were detected by two-dimensional gel electrophoresis and ESI-MS/MS. We identified 28 proteins that were upregulated by preload compared to the unloaded group (at least 1.75-fold regulation, all P < 0.05). Specifically, mechanical load upregulated a variety of enzymes involved in energy metabolism (i.e., aconitase, pyruvate kinase, fructose bisphosphate aldolase, ATP synthase alpha chain, acetyl-CoA acetyltransferase, NADH ubiquinone oxidoreductase, ubiquinol cytochrome c reductase, hydroxyacyl-CoA dehydrogenase). Cyclosporine A treatment (1 micromol/l) abolished the preload-induced upregulation of these proteins. We demonstrate for the first time that an acute increase in the myocardial preload causes upregulation of metabolic enzymes, thereby increasing the capacity of the myocardium to generate ATP production. This short-term adaptation to enhanced mechanical load appears to critically depend on calcineurin phosphatase activity.