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Streich Jr. F.C.,Structural Biology Program | Lima C.D.,Structural Biology Program | Lima C.D.,Howard Hughes Medical Institute
Annual Review of Biophysics | Year: 2014

Attachment of ubiquitin (Ub) and ubiquitin-like proteins (Ubls) to cellular proteins regulates numerous cellular processes including transcription, the cell cycle, stress responses, DNA repair, apoptosis, immune responses, and autophagy, to name a few. The mechanistically parallel but functionally distinct conjugation pathways typically require the concerted activities of three types of protein: E1 Ubl-activating enzymes, E2 Ubl carrier proteins, and E3 Ubl ligases. E1 enzymes initiate pathway specificity for each cascade by recognizing and activating cognate Ubls, followed by catalyzing Ubl transfer to cognate E2 protein(s). Under certain circumstances, the E2 Ubl complex can direct ligation to the target protein, but most often requires the cooperative activity of E3 ligases. Reviewed here are recent structural and functional studies that improve our mechanistic understanding of E1-, E2-, and E3-mediated Ubl conjugation. Copyright © 2014 by Annual Reviews. All rights reserved. Source

Acehan D.,Structural Biology Program | Acehan D.,Skirball Institute | Malhotra A.,New York University | Xu Y.,New York University | And 6 more authors.
Biophysical Journal | Year: 2011

F1F0 ATP synthase forms dimers that tend to assemble into large supramolecular structures. We show that the presence of cardiolipin is critical for the degree of oligomerization and the degree of order in these ATP synthase assemblies. This conclusion was drawn from the statistical analysis of cryoelectron tomograms of cristae vesicles isolated from Drosophila flight-muscle mitochondria, which are very rich in ATP synthase. Our study included a wild-type control, a cardiolipin synthase mutant with nearly complete loss of cardiolipin, and a tafazzin mutant with reduced cardiolipin levels. In the wild-type, the highcurvature edge of crista vesicles was densely populated with ATP synthase molecules that were typically organized in one or two rows of dimers. In both mutants, the density of ATP synthase was reduced at the high-curvature zone despite unchanged expression levels. Compared to the wild-type, dimer rows were less extended in the mutants and there was more scatter in the orientation of dimers. These data suggest that cardiolipin promotes the ribbonlike assembly of ATP synthase dimers and thus affects lateral organization and morphology of the crista membrane. © 2011 by the Biophysical Society. Source

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