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61.
The plant mitochondrial cytochrome bc
1 complex, like nonplant mitochondrial complexes,consists of cytochromes b and c
1, the Rieske iron–sulfur protein, two Core proteins, and fivelow-molecular mass subunits. However, in contrast to nonplant sources, the two Core proteinsare identical to subunits of the general mitochondrial processing peptidase (MPP). The MPPis a fascinating enzyme that catalyzes the specific cleavage of the diverse presequence peptidesfrom hundreds of the nuclear-encoded mitochondrial precursor proteins that are synthesizedin the cytosol and imported into the mitochondrion. Integration of the MPP into the bc
1complex renders the bc
1 complex in plants bifunctional, being involved both in electrontransport and in protein processing. Despite the integration of MPP into the bc
1 complex,electron transfer as well as translocation of the precursor through the import channel areindependent of the protein-processing activity. Recognition of the processing site by MPPoccurs via the recognition of higher-order structural elements in combination with charge andcleavage-site properties. Elucidation of the three-dimensional (3-D) structure of the mammaliancytochrome bc
1 complex is highly useful for understanding of the mechanism of action of MPP.In memory of my teacher—an insightful, devoted, and enthusiastic scientist and an amiable and kind-hearted human being—Lars Ernster 相似文献
62.
Ronse DE Craene LP 《Annals of botany》2004,94(5):741-751
BACKGROUND AND AIMS: On the basis of molecular evidence Berberidopsidaceae have been linked with Aextoxicaceae in an order Berberidopsidales at the base of the core Eudicots. The floral development of Berberidopsis is central to the understanding of the evolution of floral configurations at the transition of the basal Eudicots to the core Eudicots. It lies at the transition of trimerous or dimerous, simplified apetalous forms into pentamerous, petaliferous flowers. METHODS: The floral ontogeny of Berberidopsis was studied with a scanning electron microscope. KEY RESULTS: Flowers are grouped in terminal racemes with variable development. The relationship between the number of tepals, stamens and carpels is more or less fixed and floral initiation follows a strict 2/5 phyllotaxis. Two bracteoles, 12 tepals, eight stamens and three carpels are initiated in a regular sequence. The number of stamens can be increased by a doubling of stamen positions. CONCLUSIONS: The floral ontogeny of Berberidopsis provides support for the shift in floral bauplan from the basal Eudicots to the core Eudicots as a transition of a spiral flower with a 2/5 phyllotaxis to pentamerous flowers with two perianth whorls, two stamen whorls and a single carpel whorl. The differentiation of sepals and petals from bracteotepals is discussed and a comparison is made with other Eudicots with a similar configuration and development. Depending on the resolution of the relationships among the basalmost core Eudicots it is suggested that Berberidopsis either represents a critical stage in the evolution of pentamerous flowers of major clades of Eudicots, or has a floral prototype that may be at the base of evolution of flowers of other core Eudicots. The distribution of a floral Bauplan in other clades of Eudicots similar to Berberidopsidales is discussed. 相似文献
63.
Carbonic Anhydrase Activities in Pea Thylakoids 总被引:2,自引:1,他引:1
Moskvin OV Shutova TV Khristin MS Ignatova LK Villarejo A Samuelsson G Klimov VV Ivanov BN 《Photosynthesis research》2004,79(1):93-100
Pea thylakoids with high carbonic anhydrase (CA) activity (average rates of 5000 µmol H+ (mg Chl)–1 h–1 at pH 7.0) were prepared. Western blot analysis using antibodies raised against the soluble stromal -CA from spinach clearly showed that this activity is not a result of contamination of the thylakoids with the stromal CA but is derived from a thylakoid membrane-associated CA. Increase of the CA activity after partial membrane disintegration by detergent treatment, freezing or sonication implies the location of the CA in the thylakoid interior. Salt treatment of thylakoids demonstrated that while one part of the initial enzyme activity is easily soluble, the rest of it appears to be tightly associated with the membrane. CA activity being measured as HCO3
– dehydration (dehydrase activity) in Photosystem II particles (BBY) was variable and usually low. The highest and most reproducible activities (approximately 2000 µmol H+ (mg Chl)–1 h–1) were observed in the presence of detergents (Triton X-100 or n-octyl--D-glucopyranoside) in low concentrations. The dehydrase CA activity of BBY particles was more sensitive to the lipophilic CA inhibitor, ethoxyzolamide, than to the hydrophilic CA inhibitor, acetazolamide. CA activity was detected in PS II core complexes with average rate of 13,000 µmol H+ (mg Chl)–1 h–1 which was comparable to CA activity in BBY particles normalized on a PS II reaction center basis.This revised version was published online in October 2005 with corrections to the Cover Date. 相似文献
64.
A molecular phylogeny of enteric bacteria and implications for a bacterial species concept 总被引:1,自引:0,他引:1
A molecular phylogeny for seven taxa of enteric bacteria (Citrobacter freundii, Enterobacter cloacae, Escherichia coli, Hafnia alvei, Klebsiella oxytoca, Klebsiella pneumoniae, and Serratia plymuthica) was made from multiple isolates per taxa taken from a collection of environmental enteric bacteria. Sequences from five housekeeping genes (gapA, groEL, gyrA, ompA, and pgi) and the 16S rRNA gene were used to infer individual gene trees and were concatenated to infer a composite molecular phylogeny for the species. The isolates from each taxa formed tight species clusters in the individual gene trees, suggesting the existence of 'genotypic' clusters that correspond to traditional species designations. These sequence data and the resulting gene trees and consensus tree provide the first data set with which to assess the utility of the recently proposed core genome hypothesis (CGH). The CGH provides a genetically based approach to applying the biological species concept to bacteria. 相似文献
65.
Chakrabarti S Kobayashi KS Flavell RA Marks CB Miyake K Liston DR Fowler KT Gorelick FS Andrews NW 《The Journal of cell biology》2003,162(4):543-549
Members of the synaptotagmin family have been proposed to function as Ca2+ sensors in membrane fusion. Syt VII is a ubiquitously expressed synaptotagmin previously implicated in plasma membrane repair and Trypanosoma cruzi invasion, events which are mediated by the Ca2+-regulated exocytosis of lysosomes. Here, we show that embryonic fibroblasts from Syt VII-deficient mice are less susceptible to trypanosome invasion, and defective in lysosomal exocytosis and resealing after wounding. Examination of mutant mouse tissues revealed extensive fibrosis in the skin and skeletal muscle. Inflammatory myopathy, with muscle fiber invasion by leukocytes and endomysial collagen deposition, was associated with elevated creatine kinase release and progressive muscle weakness. Interestingly, similar to what is observed in human polymyositis/dermatomyositis, the mice developed a strong antinuclear antibody response, characteristic of autoimmune disorders. Thus, defective plasma membrane repair in tissues under mechanical stress may favor the development of inflammatory autoimmune disease. 相似文献
66.
Muthurajan UM Park YJ Edayathumangalam RS Suto RK Chakravarthy S Dyer PN Luger K 《Biopolymers》2003,68(4):547-556
The last five years have seen exciting advances in our understanding of the structure of the nucleosome core particle, the basic repeating unit in all eukaryotic chromatin. A picture emerges in which nucleosomal DNA, while distorted and compacted fivefold by tight interactions with the histone octamer core, is at the same time highly dynamic and adaptable. Here, we summarize the salient features from recent structural studies of nucleosome core particles (both published and unpublished) that concern the structure and dynamics of nucleosomal DNA, and the nature of protein-DNA interactions. Current mechanisms for chromatin remodeling and nucleosome sliding are discussed in light of new structural evidence. Finally, techniques to study nucleosome stability and ultimately dynamics are introduced. 相似文献
67.
Two forms of cytochrome b(5) have been identified, associated with the outer membrane of liver mitochondria (OM cyt b(5)) and with the membrane of the endoplasmic reticulum (microsomal, Mc cyt b(5)). These proteins have very similar structures, but differ significantly in physical properties, with the OM cyt b(5) exhibiting a more negative reduction potential, higher stability, and stronger interactions with the heme. We perform molecular dynamics simulations to probe the structures and fluctuations of the two proteins in solution, to help explain the observed physical differences. We find that the structures of the two proteins, highly similar in the crystal, differ in position of a surface loop involving residues 49-51 in solution. Hydrophobic residues Ala-18, Ile-32, Leu-36, and Leu-47 tend to cluster together on the surface of rat OM cyt b(5), blocking water access to the protein interior. In bovine Mc cyt b(5), two of these positions, Ser-18 and Arg-47, are occupied by hydrophilic residues. This leads to breaking the hydrophobic cluster and allowing the protein to occupy a more open conformation. A measure of this structural transition is the opening of a cleft on the protein surface, which is 5 A wider in the OM cyt b(5) simulation compared to the Mc form. The OM protein also appears to have a more compact hydrophobic core in its beta-sheet region. These effects may be used to explain observed stability differences between the two proteins. 相似文献
68.
Improving the performance of Rosetta using multiple sequence alignment information and global measures of hydrophobic core formation 总被引:7,自引:0,他引:7
This study explores the use of multiple sequence alignment (MSA) information and global measures of hydrophobic core formation for improving the Rosetta ab initio protein structure prediction method. The most effective use of the MSA information is achieved by carrying out independent folding simulations for a subset of the homologous sequences in the MSA and then identifying the free energy minima common to all folded sequences via simultaneous clustering of the independent folding runs. Global measures of hydrophobic core formation, using ellipsoidal rather than spherical representations of the hydrophobic core, are found to be useful in removing non-native conformations before cluster analysis. Through this combination of MSA information and global measures of protein core formation, we significantly increase the performance of Rosetta on a challenging test set. Proteins 2001;43:1-11. 相似文献
69.
Electrostatic interactions are important for protein folding. At low resolution, the electrostatic field of the whole molecule can be described in terms of charge center(s). To study electrostatic effects, the centers of positive and negative charge were calculated for 20 small proteins of known structure, for which hydrogen exchange cores had been determined experimentally. Two observations seem to be important. First, in all 20 proteins studied 30-100% of the residues forming hydrogen exchange core(s) were clustered around the charge centers. Moreover, in each protein more than half of the core sequences are located near the centers of charge. Second, the general architecture of all-alpha proteins from the set seems to be stabilized by interactions of residues surrounding the charge centers. In most of the alpha-beta proteins, either or both of the centers are located near a pair of consecutive strands, and this is even more characteristic for alpha/Beta and all-beta structures. Consecutive strands are very probable sites of early folding events. These two points lead to the conclusion that charge centers, defined solely from the structure of the folded protein may indicate the location of a protein's hydrogen exchange/folding core. In addition, almost all the proteins contain well-conserved continuous hydrophobic sequences of three or more residues located in the vicinity of the charge centers. These hydrophobic sequences may be primary nucleation sites for protein folding. The results suggest the following scheme for the order of events in folding: local hydrophobic nucleation, electrostatic collapse of the core, global hydrophobic collapse, and slow annealing to the native state. This analysis emphasizes the importance of treating electrostatics during protein-folding simulations. 相似文献
70.
The role of aromatic residues in the hydrophobic core of the villin headpiece subdomain 总被引:1,自引:0,他引:1 下载免费PDF全文
Frank BS Vardar D Buckley DA McKnight CJ 《Protein science : a publication of the Protein Society》2002,11(3):680-687
Small autonomously folding proteins are of interest as model systems to study protein folding, as the same molecule can be used for both experimental and computational approaches. The question remains as to how well these minimized peptide model systems represent larger native proteins. For example, is the core of a minimized protein tolerant to mutation like larger proteins are? Also, do minimized proteins use special strategies for specifying and stabilizing their folded structure? Here we examine these questions in the 35‐residue autonomously folding villin headpiece subdomain (VHP subdomain). Specifically, we focus on a cluster of three conserved phenylalanine (F) residues F47, F51, and F58, that form most of the hydrophobic core. These three residues are oriented such that they may provide stabilizing aromatic–aromatic interactions that could be critical for specifying the fold. Circular dichroism and 1D‐NMR spectroscopy show that point mutations that individually replace any of these three residues with leucine were destabilized, but retained the native VHP subdomain fold. In pair‐wise replacements, the double mutant that retains F58 can adopt the native fold, while the two double mutants that lack F58 cannot. The folding of the double mutant that retains F58 demonstrates that aromatic–aromatic interactions within the aromatic cluster are not essential for specifying the VHP subdomain fold. The ability of the VHP subdomain to tolerate mutations within its hydrophobic core indicates that the information specifying the three dimensional structure is distributed throughout the sequence, as observed in larger proteins. Thus, the VHP subdomain is a legitimate model for larger, native proteins. 相似文献