Alternative complex III (ACIII) couples quinol oxidation and electron acceptor reduction with potential transmembrane proton translocation. It is compositionally and structurally different from the cytochrome bc1/b6f complexes but functionally replaces these enzymes in the photosynthetic and/or respiratory electron transport chains (ETCs) of many bacteria. However, the true compositions and architectures of ACIIIs remain unclear, as do their structural and functional relevance in mediating the ETCs.
View Article and Find Full Text PDFRoseiflexus castenholzii is a gram-negative filamentous phototrophic bacterium that carries out anoxygenic photosynthesis through a cyclic electron transport chain (ETC). The ETC is composed of a reaction center (RC)-light-harvesting (LH) complex (rcRC-LH); an alternative complex III (rcACIII), which functionally replaces the cytochrome bc/bf complex; and the periplasmic electron acceptor auracyanin (rcAc). Although compositionally and structurally different from the bc/bf complex, rcACIII plays similar essential roles in oxidizing menaquinol and transferring electrons to the rcAc.
View Article and Find Full Text PDFMalonyl-CoA reductase (MCR) is a NADPH-dependent bi-functional enzyme that performs alcohol dehydrogenase and aldehyde dehydrogenase (CoA-acylating) activities in the N- and C-terminal fragments, respectively. It catalyzes the two-step reduction of malonyl-CoA to 3-hydroxypropionate (3-HP), a key reaction in the autotrophic CO fixation cycles of green non-sulfur bacteria and the archaea . However, the structural basis underlying substrate selection, coordination, and the subsequent catalytic reactions of full-length MCR is largely unknown.
View Article and Find Full Text PDFis an ancient green non-sulfur bacteria that absorbs the solar energy through bacteriochlorophylls (BChls) bound in the only light harvesting (LH) complex, and transfers to the reaction center (RC), wherein primary charge separation occurs and transforms the energy into electrochemical potentials. In contrast to purple bacteria, RC-LH (RC-LH) does not contain an H subunit. Instead, a tightly bound tetraheme cytochrome subunit is exposed on the P-side of the RC, which contains three BChls, three bacteriopheophytins (BPheos), two menaquinones, and one iron for electron transfer.
View Article and Find Full Text PDFATM/Tel1 is an apical kinase that orchestrates the multifaceted DNA damage response. Mutations of ATM/Tel1 are associated with ataxia telangiectasia syndrome. Here, we report cryo-EM structures of symmetric dimer (4.
View Article and Find Full Text PDFThe ataxia telangiectasia-mutated and Rad3-related (ATR) kinase is a master regulator of DNA damage response and replication stress in humans, but the mechanism of its activation remains unclear. ATR acts together with its partner ATRIP. Using cryo-electron microscopy, we determined the structure of intact Mec1-Ddc2 (the yeast homolog of ATR-ATRIP), which is poised for catalysis, at a resolution of 3.
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