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Articles by Fevzi Daldal
Total Records ( 4 ) for Fevzi Daldal
  Yan Zhang , Elise R. Lyver , Eiko Nakamaru-Ogiso , Heeyong Yoon , Boominathan Amutha , Dong- Woo Lee , Erfei Bi , Tomoko Ohnishi , Fevzi Daldal , Debkumar Pain and Andrew Dancis
  In a forward genetic screen for interaction with mitochondrial iron carrier proteins in Saccharomyces cerevisiae, a hypomorphic mutation of the essential DRE2 gene was found to confer lethality when combined with Δmrs3 and Δmrs4. The dre2 mutant or Dre2-depleted cells were deficient in cytosolic Fe/S cluster protein activities while maintaining mitochondrial Fe/S clusters. The Dre2 amino acid sequence was evolutionarily conserved, and cysteine motifs (CX2CXC and twin CX2C) in human and yeast proteins were perfectly aligned. The human Dre2 homolog (implicated in blocking apoptosis and called CIAPIN1 or anamorsin) was able to complement the nonviability of a Δdre2 deletion strain. The Dre2 protein with triple hemagglutinin tag was located in the cytoplasm and in the mitochondrial intermembrane space. Yeast Dre2 overexpressed and purified from bacteria was brown and exhibited signature absorption and electron paramagnetic resonance spectra, indicating the presence of both [2Fe-2S] and [4Fe-4S] clusters. Thus, Dre2 is an essential conserved Fe/S cluster protein implicated in extramitochondrial Fe/S cluster assembly, similar to other components of the so-called CIA (cytoplasmic Fe/S cluster assembly) pathway although partially localized to the mitochondrial intermembrane space.
  Yavuz Ozturk , Dong- Woo Lee , Sevnur Mandaci , Artur Osyczka , Roger C. Prince and Fevzi Daldal
  Photosynthetic (Ps) electron transport pathways often contain multiple electron carriers with overlapping functions. Here we focus on two c-type cytochromes (cyt) in facultative phototrophic bacteria of the Rhodobacter genus: the diffusible cyt c2 and the membrane-anchored cyt cy. In species like R. capsulatus, cyt cy functions in both Ps and respiratory electron transport chains, whereas in other species like R. sphaeroides, it does so only in respiration. The molecular bases of this difference was investigated by producing a soluble variant of cyt cy (S-cy), by fusing genetically the cyt c2 signal sequence to the cyt c domain of cyt cy. This novel electron carrier was unable to support the Ps growth of R. capsulatus. However, strains harboring cyt S-cy regained Ps growth ability by acquiring mutations in its cyt c domain. They produced cyt S-cy variants at amounts comparable with that of cyt c2, and conferred Ps growth. Chemical titration indicated that the redox midpoint potential of cyt S-cy was about 340 mV, similar to that of cyts c2 or cy. Remarkably, electron transfer kinetics from the cyt bc1 complex to the photochemical reaction center (RC) mediated by cyt S-cy was distinct from those seen with the cyt c2 or cyt cy. The kinetics exhibited a pronounced slow phase, suggesting that cyt S-cy interacted with the RC less tightly than cyt c2. Comparison of structural models of cyts c2 and S-cy revealed that several of the amino acid residues implicated in long-range electrostatic interactions promoting binding of cyt c2 to the RC are not conserved in cyt cy, whereas those supporting short-range hydrophobic interactions are conserved. These findings indicated that attaching electron carrier cytochromes to the membrane allowed them to weaken their interactions with their partners so that they could accommodate more rapid multiple turnovers.
  Dong- Woo Lee , Yavuz Ozturk , Artur Osyczka , Jason W. Cooley and Fevzi Daldal
  Photosynthetic (Ps) growth of purple non-sulfur bacteria such as Rhodobacter capsulatus depends on the cyclic electron transfer (ET) between the ubihydroquinone (QH2): cytochrome (cyt) c oxidoreductases (cyt bc1 complex), and the photochemical reaction centers (RC), mediated by either a membrane-bound (cyt cy) or a freely diffusible (cyt c2) electron carrier. Previously, we constructed a functional cyt bc1-cy fusion complex that supported Ps growth solely relying on membrane-confined ET ( Lee, D.-W., Ozturk, Y., Mamedova, A., Osyczka, A., Cooley, J. W., and Daldal, F. (2006) Biochim. Biophys. Acta 1757, 346-352 [Medline] [Order article via Infotrieve] ). In this work, we further characterized this cyt bc1-cy fusion complex, and used its derivatives with shorter cyt cy linkers as "molecular rulers" to probe the distances separating the Ps components. Comparison of the physicochemical properties of both membrane-embedded and purified cyt bc1-cy fusion complexes established that these enzymes were matured and assembled properly. Light-activated, time-resolved kinetic spectroscopy analyses revealed that their variants with shorter cyt cy linkers exhibited fast, native-like ET rates to the RC via the cyt bc1. However, shortening the length of the cyt cy linker decreased drastically this electronic coupling between the cyt bc1-cy fusion complexes and the RC, thereby limiting Ps growth. The shortest and still functional cyt cy linker was about 45 amino acids long, showing that the minimal distance allowed between the cyt bc1-cy fusion complexes and the RC and their surrounding light harvesting proteins was very short. These findings support the notion that membrane-bound Ps components form large, active structural complexes that are "hardwired" for cyclic ET.
  Marcin Sarewicz , Arkadiusz Borek , Fevzi Daldal , Wojciech Froncisz and Artur Osyczka
  One of the steps of a common pathway for biological energy conversion involves electron transfer between cytochrome c and cytochrome bc1. To clarify the mechanism of this reaction, we examined the structural association of those two proteins using the electron transfer-independent electron paramagnetic resonance (EPR) techniques. Drawing on the differences in the continuous wave EPR spectra and saturation recoveries of spin-labeled bacterial and mitochondrial cytochromes c recorded in the absence and presence of bacterial cytochrome bc1, we have exposed a time scale of dynamic equilibrium between the bound and the free state of cytochrome c at various ionic strengths. Our data show a successive decrease of the bound cytochrome c fraction as the ionic strength increases, with a limit of ~120 mM NaCl above which essentially no bound cytochrome c can be detected by EPR. This limit does not apply to all of the interactions of cytochrome c with cytochrome bc1 because the cytochrome bc1 enzymatic activity remained high over a much wider range of ionic strengths. We concluded that EPR monitors just the tightly bound state of the association and that an averaged lifetime of this state decreases from over 100 µs at low ionic strength to less than 400 ns at an ionic strength above 120 mM. This suggests that at physiological ionic strength, the tightly bound complex on average lasts less than the time needed for a single electron exchange between hemes c and c1, indicating that productive electron transfer requires several collisions of the two molecules. This is consistent with an early idea of diffusion-coupled reactions that link the soluble electron carriers with the membranous complexes, which, we believe, provides a robust means of regulating electron flow through these complexes.
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