Oligomer | EPFL Graph Search

In chemistry and biochemistry, an oligomer (əˈlɪgəmər) is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers. The name is composed of Greek elements oligo-, "a few" and -mer, "parts". An adjective form is oligomeric. The oligomer concept is contrasted to that of a polymer, which is usually understood to have a large number of units, possibly thousands or millions. However, there is no sharp distinction between these two concepts. One proposed criterion is whether the molecule's properties vary significantly with the removal of one or a few of the units. An oligomer with a specific number of units is referred to by the Greek prefix denoting that number, with the ending -mer: thus dimer, trimer, tetramer, pentamer, and hexamer refer to molecules with two, three, four, five, and six units, respectively. The units of an oligomer may be arranged in a linear cha

Oligomerization of the alpha 1a- and alpha 1b-Adrenergic Receptor Subtypes: Potential Implications in Receptor Internalization

Susanna Cotecchia, Jean-Baptiste Perez, Laura Stanasila, Horst Vogel

We combined biophys., biochem., and pharmacol. approaches to investigate the ability of the a1a- and a1b-adrenergic receptor (AR) subtypes to form homo- and hetero-oligomers. Receptors tagged with different epitopes (hemagglutinin and Myc) or fluorescent proteins (cyan and green fluorescent proteins) were transiently expressed in HEK-293 cells either individually or in different combinations. Fluorescence resonance energy transfer measurements provided evidence that both the a1a- and a1b-AR can form homo-oligomers with similar transfer efficiency of .apprx.0.10. Hetero-oligomers could also be obsd. between the a1b- and the a1a-AR subtypes but not between the a1b-AR and the b2-AR, the NK1 tachykinin, or the CCR5 chemokine receptors. Oligomerization of the a1b-AR did not require the integrity of its C-tail, of two glycophorin motifs, or of the N-linked glycosylation sites at its N terminus. In contrast, helix I and, to a lesser extent, helix VII were found to play a role in the a1b-AR homo-oligomerization. Receptor oligomerization was not influenced by the agonist epinephrine or by the inverse agonist prazosin. A constitutively active (A293E) as well as a signaling-deficient (R143E) mutant displayed oligomerization features similar to those of the wild type a1b-AR. Confocal imaging revealed that oligomerization of the a1-AR subtypes correlated with their ability to co-internalize upon exposure to the agonist. The a1a-selective agonist oxymetazoline induced the co-internalization of the a1a- and a1b-AR, whereas the a1b-AR could not co-internalize with the NK1 tachykinin or CCR5 chemokine receptors. Oligomerization might therefore represent an addnl. mechanism regulating the physiol. responses mediated by the a1a- and a1b-AR subtypes. [on SciFinder (R)]

2003

Monitoring alpha-synuclein oligomerization and aggregation using bimolecular fluorescence complementation assays: What you see is not always what you get

Abdelrahman Mohammed Adel Elsaeed Mansour AlOkda, Bryan Frey, Hilal Lashuel, Nathan Alain Denis Riguet

Bimolecular fluorescence complementation (BiFC) was introduced a decade ago as a method to monitor alpha-synuclein (alpha-syn) oligomerization in intact cells. Since then, several alpha-syn BiFC cellular assays and animal models have been developed based on the assumption that an increase in the fluorescent signal correlates with increased alpha-syn oligomerization or aggregation. Despite the increasing use of these assays and models in mechanistic studies, target validation and drug screening, there have been no reports that (1) validate the extent to which the BiFC fluorescent signal correlates with alpha-syn oligomerization at the biochemical level; (2) provide a structural characterization of the oligomers and aggregates formed by the BiFC. To address this knowledge gap, we first analysed the expression level and oligomerization properties of the individual constituents of alpha-syn-Venus, one of the most commonly used BiFC systems, in HEK-293 & SH-SY5Y cells from three different laboratories using multiple biochemical approaches and techniques. Next, we investigated the biochemical and aggregation properties of alpha-syn upon co-expression of both BiFC fragments. Our results show that (1) the C-terminal-Venus fused to alpha-syn (alpha-syn-Vc) is present in much lower abundance than its counterpart with N-terminal-Venus fused to alpha-syn (Vn-alpha-syn); (2) Vn-alpha-syn exhibits a high propensity to form oligomers and higher-order aggregates; and (3) the expression of either or both fragments does not result in the formation of alpha-syn fibrils or cellular inclusions. Furthermore, our results suggest that only a small fraction of Vn-alpha-syn is involved in the formation of the fluorescent BiFC complex and that some of the fluorescent signal may arise from the association or entrapment of alpha-syn-Vc in Vn-alpha-syn aggregates. The fact that the N-terminal fragment exists predominantly in an aggregated state also indicates that one must exercise caution when using this system to investigate alpha-syn oligomerization in cells or in vivo. Altogether, our results suggest that cellular and animal models of oligomerization, aggregation and cell-to-cell transmission based on the alpha-syn BiFC systems should be thoroughly characterized at the biochemical level to ensure that they reproduce the process of interest and measure what they are intended to measure.

2020

Structural differences of amyloid-beta fibrils revealed by antibodies from phage display

Patrick Droste, Hilal Lashuel

Background: Beside neurofibrillary tangles, amyloid plaques are the major histological hallmarks of Alzheimer's disease (AD) being composed of aggregated fibrils of beta-amyloid (A beta). During the underlying fibrillogenic pathway, starting from a surplus of soluble A beta and leading to mature fibrils, multiple conformations of this peptide appear, including oligomers of various shapes and sizes. To further investigate the fibrillization of beta-amyloid and to have tools at hand to monitor the distribution of aggregates in the brain or even act as disease modulators, it is essential to develop highly sensitive antibodies that can discriminate between diverse aggregates of A beta. Results: Here we report the generation and characterization of a variety of amyloid-beta specific human and human-like antibodies. Distinct fractions of monomers and oligomers of various sizes were separated by size exclusion chromatography (SEC) from A beta 42 peptides. These antigens were used for the generation of two A beta 42 specific immune scFv phage display libraries from macaque (Macaca fascicularis). Screening of these libraries as well as two naive human phage display libraries resulted in multiple unique binders specific for amyloid-beta. Three of the obtained antibodies target the N-terminal part of A beta 42 although with varying epitopes, while another scFv binds to the a-helical central region of the peptide. The affinities of the antibodies to various A beta 42 aggregates as well as their ability to interfere with fibril formation and disaggregation of preformed fibrils were determined. Most significantly, one of the scFv is fibril-specific and can discriminate between two different fibril forms resulting from variations in the acidity of the milieu during fibrillogenesis. Conclusion: We demonstrated that the approach of animal immunization and subsequent phage display based antibody selection is applicable to generate highly specific anti beta-amyloid scFvs that are capable of accurately discriminating between minute conformational differences.

Biomed Central Ltd2015