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Two distinct conformations of Abeta aggregates on the surface of living PC12 cells.

ABSTRACT: Abeta42 has been found to associate rapidly to neuronal cells and is the primary constituent of senile plaques. In this study we monitored the aggregation of Abeta42 with living PC12 cells. Using photobleaching Förster resonance energy transfer, we observed one set of aggregates that displayed colocalization and another that displayed energy transfer. Cell surface aggregates were found to become resistant to potassium iodide (KI)-induced quenching. Exposed Abeta42 regions were probed with three monoclonal antibodies directed against the N-terminus, an internal sequence, and the C-terminus of Abeta42. Two populations of aggregates were revealed: one that bound all three antibodies, and one that bound all but the C-terminus antibody. Of interest, using fluorescent recovery after photobleaching, we observed no Abeta42 exchange within either type of aggregate. These findings offer what we believe is new insight into the conformations of Abeta42 that accumulate on the surface of living cells. One conformation is incapable of energy transfer, is sensitive to KI, and binds C-terminus-specific antibodies. The other conformation increases in number over time, is capable of energy transfer, is quencher-resistant, and has a sequestered C-terminus. With further studies to characterize Abeta aggregation on live cells, the underlying mechanisms leading to Alzheimer's disease may be revealed.

SUBMITTER: Bateman DA

PROVIDER: S-EPMC2712147 | biostudies-literature | 2009 May

REPOSITORIES: biostudies-literature

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Two distinct conformations of Abeta aggregates on the surface of living PC12 cells.

Bateman David A DA Chakrabartty Avijit A

Biophysical journal 20090501 10

Abeta42 has been found to associate rapidly to neuronal cells and is the primary constituent of senile plaques. In this study we monitored the aggregation of Abeta42 with living PC12 cells. Using photobleaching Förster resonance energy transfer, we observed one set of aggregates that displayed colocalization and another that displayed energy transfer. Cell surface aggregates were found to become resistant to potassium iodide (KI)-induced quenching. Exposed Abeta42 regions were probed with three ...[more]

PMID: 19450496

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Project description:SWEETs and their prokaryotic homologues are monosaccharide and disaccharide transporters that are present from Archaea to plants and humans. SWEETs play crucial roles in cellular sugar efflux processes: that is, in phloem loading, pollen nutrition and nectar secretion. Their bacterial homologues, which are called SemiSWEETs, are among the smallest known transporters. Here we show that SemiSWEET molecules, which consist of a triple-helix bundle, form symmetrical, parallel dimers, thereby generating the translocation pathway. Two SemiSWEET isoforms were crystallized, one in an apparently open state and one in an occluded state, indicating that SemiSWEETs and SWEETs are transporters that undergo rocking-type movements during the transport cycle. The topology of the triple-helix bundle is similar yet distinct to that of the basic building block of animal and plant major facilitator superfamily (MFS) transporters (for example, GLUTs and SUTs). This finding indicates two possibilities: that SWEETs and MFS transporters evolved from an ancestral triple-helix bundle or that the triple-helix bundle represents convergent evolution. In SemiSWEETs and SWEETs, two triple-helix bundles are arranged in a parallel configuration to produce the 6- and 6 + 1-transmembrane-helix pores, respectively. In the 12-transmembrane-helix MFS transporters, four triple-helix bundles are arranged into an alternating antiparallel configuration, resulting in a much larger 2 × 2 triple-helix bundle forming the pore. Given the similarity of SemiSWEETs and SWEETs to PQ-loop amino acid transporters and to mitochondrial pyruvate carriers (MPCs), the structures characterized here may also be relevant to other transporters in the MtN3 clan. The insight gained from the structures of these transporters and from the analysis of mutations of conserved residues will improve the understanding of the transport mechanism, as well as allow comparative studies of the different superfamilies involved in sugar transport and the evolution of transporters in general.

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Two distinct conformations of Abeta aggregates on the surface of living PC12 cells.

Publications

Two distinct conformations of Abeta aggregates on the surface of living PC12 cells.

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