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911.
912.
Soil aggregates can provide an effective protection of organic matter against microbial decomposition as reported by several
macroaggregate disruption studies. However, research on the role of aggregation for carbon mineralization was mainly focused
on arable soils. In the present study we aim to clarify the impact of aggregation on organic matter protection by measuring
carbon mineralization in terms of microbial respiration rates of intact macroaggregates (2–4 and 4–8 mm) and corresponding
crushed aggregates from seven topsoil horizons from both arable and forest sites. For two arable and one forest soil we found
a significantly (P < 0.001) lower carbon mineralization from intact aggregates as compared to the corresponding crushed material. The portion
of aggregate protected carbon reached up to 30% for a grassland soil. For the other arable and forest soils no significant
effect of aggregation was found. Similarly, no clear trend could be found for the protective capacity of different size fractions.
We conclude that protection by aggregation is effective primarily for soils with a large pool of labile organic matter regardless
of their usage as arable land or forest. 相似文献
913.
Entomopathogenic fungi were recorded from field samples of the harlequin ladybird Harmonia axyridis, an invasive coccinellid that has recently arrived in Denmark. Larvae, pupae and adults were found to be infected by Isaria farinosa, Beauveria bassiana and species of Lecanicillium. This is the first record of entomopathogenic fungi infecting larvae and pupae. Winter mortality due to fungal infection reached 17.9% in adults collected at one location. The larval stage was most susceptible to fungal infection, as confirmed through bioassay with I. farinosa. 相似文献
914.
Fredrik I. Andersson Anders Tryggvesson Michal Sharon Alexander V. Diemand Mirjam Classen Christoph Best Ronny Schmidt Jenny Schelin Tara M. Stanne Bernd Bukau Carol V. Robinson Susanne Witt Axel Mogk Adrian K. Clarke 《The Journal of biological chemistry》2009,284(20):13519-13532
The Clp protease is conserved among eubacteria and most eukaryotes, and
uses ATP to drive protein substrate unfolding and translocation into a chamber
of sequestered proteolytic active sites. The main constitutive Clp protease in
photosynthetic organisms has evolved into a functionally essential and
structurally intricate enzyme. The model Clp protease from the cyanobacterium
Synechococcus consists of the HSP100 molecular chaperone ClpC and a
mixed proteolytic core comprised of two distinct subunits, ClpP3 and ClpR. We
have purified the ClpP3/R complex, the first for a Clp proteolytic core
comprised of heterologous subunits. The ClpP3/R complex has unique functional
and structural features, consisting of twin heptameric rings each with an
identical ClpP33ClpR4 configuration. As predicted by its
lack of an obvious catalytic triad, the ClpR subunit is shown to be
proteolytically inactive. Interestingly, extensive modification to ClpR to
restore proteolytic activity to this subunit showed that its presence in the
core complex is not rate-limiting for the overall proteolytic activity of the
ClpCP3/R protease. Altogether, the ClpP3/R complex shows remarkable
similarities to the 20 S core of the proteasome, revealing a far greater
degree of convergent evolution than previously thought between the development
of the Clp protease in photosynthetic organisms and that of the eukaryotic 26
S proteasome.Proteases perform numerous tasks vital for cellular homeostasis in all
organisms. Much of the selective proteolysis within living cells is performed
by multisubunit chaperone-protease complexes. These proteases all share a
common two-component architecture and mode of action, with one of the best
known examples being the proteasome in archaebacteria, certain eubacteria, and
eukaryotes (1).The 20 S proteasome is a highly conserved cylindrical structure composed of
two distinct types of subunits, α and β. These are organized in
four stacked heptameric rings, with two central β-rings sandwiched
between two outer α-rings. Although the α- and β-protein
sequences are similar, it is only the latter that is proteolytic active, with
a single Thr active site at the N terminus. The barrel-shaped complex is
traversed by a central channel that widens up into three cavities. The
catalytic sites are positioned in the central chamber formed by the
β-rings, adjacent to which are two antechambers conjointly built up by
β- and α-subunits. In general, substrate entry into the core
complex is essentially blocked by the α-rings, and thus relies on the
associating regulatory partner, PAN and 19 S complexes in archaea and
eukaryotes, respectively (1).
Typically, the archaeal core structure is assembled from only one type of
α- and β-subunit, so that the central proteolytic chamber contains
14 catalytic active sites (2).
In contrast, each ring of the eukaryotic 20 S complex has seven distinct
α- and β-subunits. Moreover, only three of the seven
β-subunits in each ring are proteolytically active
(3). Having a strictly
conserved architecture, the main difference between the 20 S proteasomes is
one of complexity. In mammalian cells, the three constitutive active subunits
can even be replaced with related subunits upon induction by
γ-interferon to generate antigenic peptides presented by the class 1
major histocompatibility complex
(4).Two chambered proteases architecturally similar to the proteasome also
exist in eubacteria, HslV and ClpP. HslV is commonly thought to be the
prokaryotic counterpart to the 20 S proteasome mainly because both are Thr
proteases. A single type of HslV protein, however, forms a proteolytic chamber
consisting of twin hexameric rather than heptameric rings
(5). Also displaying structural
similarities to the proteasome is the unrelated ClpP protease. The model Clp
protease from Escherichia coli consists of a proteolytic ClpP core
flanked on one or both sides by the ATP-dependent chaperones ClpA or ClpX
(6). The ClpP proteolytic
chamber is comprised of two opposing homo-heptameric rings with the catalytic
sites harbored within (7). ClpP
alone displays only limited peptidase activity toward short unstructured
peptides (8). Larger native
protein substrates need to be recognized by ClpA or ClpX and then translocated
in an unfolded state into the ClpP proteolytic chamber
(9,
10). Inside, the unfolded
substrate is bound in an extended manner to the catalytic triads (Ser-97,
His-122, and Asp-171) and degraded into small peptide fragments that can
readily diffuse out (11).
Several adaptor proteins broaden the array of substrates degraded by a Clp
protease by binding to the associated HSP100 partner and modifying its protein
substrate specificity (12,
13). One example is the
adaptor ClpS that interacts with ClpA (EcClpA) and targets N-end rule
substrates for degradation by the ClpAP protease
(14).Like the proteasome, the Clp protease is found in a wide variety of
organisms. Besides in all eubacteria, the Clp protease also exist in mammalian
and plant mitochondria, as well as in various plastids of algae and plants. It
also occurs in the unusual plastid in Apicomplexan protozoan
(15), a family of parasites
responsible for many important medical and veterinary diseases such as
malaria. Of all these organisms, photobionts have by far the most diverse
array of Clp proteins. This was first apparent in cyanobacteria, with the
model species Synechococcus elongatus having 10 distinct Clp
proteins, four HSP100 chaperones (ClpB1–2, ClpC, and ClpX), three ClpP
proteins (ClpP1–3), a ClpP-like protein termed ClpR, and two adaptor
proteins (ClpS1–2) (16).
Of particular interest is the ClpR variant, which has protein sequence
similarity to ClpP but appears to lack the catalytic triad of Ser-type
proteases (17). This diversity
of Clp proteins is even more extreme in photosynthetic eukaryotes, with at
least 23 different Clp proteins in the higher plant Arabidopsis
thaliana, most of which are plastid-localized
(18).We have recently shown that two distinct Clp proteases exist in
Synechococcus, both of which contain mixed proteolytic cores. The
first consists of ClpP1 and ClpP2 subunits, and associates with ClpX, whereas
the other has a proteolytic core consisting of ClpP3 and ClpR that binds to
ClpC, as do the two ClpS adaptors
(19). Of these proteases, it
is the more constitutively abundant ClpCP3/R that is essential for cell
viability and growth (20,
21). It is also the ClpP3/R
complex that is homologous to the single type in eukaryotic plastids, all of
which also have ClpC as the chaperone partner
(16). In algae and plants,
however, the complexity of the plastidic Clp proteolytic core has evolved
dramatically. In Arabidopsis, the core complex consists of five ClpP
and four ClpR paralogs, along with two unrelated Clp proteins unique to higher
plants (22). Like ClpP3/R, the
plastid Clp protease in Arabidopsis is essential for normal growth
and development, and appears to function primarily as a housekeeping protease
(23,
24).One of the most striking developments in the Clp protease in photosynthetic
organisms and Apicomplexan parasites is the inclusion of ClpR within the
central proteolytic core. Although this type of Clp protease has evolved into
a vital enzyme, little is known about its activity or the exact role of ClpR
within the core complex. To address these points we have purified the intact
Synechococcus ClpP3/R proteolytic core by co-expression in E.
coli. The recombinant ClpP3/R forms a double heptameric ring complex,
with each ring having a specific ClpP3/R stoichiometry and arrangement.
Together with ClpC, the ClpP3/R complex degrades several polypeptide
substrates, but at a rate considerably slower than that by the E.
coli ClpAP protease. Interestingly, although ClpR is shown to be
proteolytically inactive, its inclusion in the core complex is not
rate-limiting to the overall activity of the ClpCP3/R protease. In general,
the results reveal remarkable similarities between the evolutionary
development of the Clp protease in photosynthetic organisms and the eukaryotic
proteasome relative to their simpler prokaryotic counterparts. 相似文献
915.
Goessler UR Bugert P Bieback K Stern-Straeter J Bran G Sadick H Hörmann K Riedel F 《Journal of cellular and molecular medicine》2009,13(6):1175-1184
The use of adult mesenchymal stem cells (MSC) in cartilage tissue engineering has been implemented in the field of regenerative medicine and offers new perspectives in the generation of transplants for reconstructive surgery. The extracellular matrix (ECM) plays a key role in modulating function and phenotype of the embedded cells and contains the integrins as adhesion receptors mediating cell-cell and cell-matrix interactions. In our study, characteristic changes in integrin expression during the course of chondrogenic differentiation of MSC from bone marrow and foetal cord blood were compared. MSC were isolated from bone marrow biopsies and cord blood. During cell culture, chondrogenic differentiation was performed. The expression of integrins and their signalling components were analysed with microarray and immunohistochemistry in freshly isolated MSC and after chondrogenic differentiation. The fibronectin-receptor (integrin a5b1) was expressed by undifferentiated MSC, expression rose during chondrogenic differentiation in both types of MSC. The components of the vitronectin/osteopontin-receptors (avb5) were not expressed by freshly isolated MSC, expression rose with ongoing differentiation. Receptors for collagens (a1b1, a2b1, a3b1) were weakly expressed by undifferentiated MSC and were activated during differentiation. As intracellular signalling components integrin linked kinase (ILK) and CD47 showed increasing expression with ongoing differentiation. For all integrins, no significant differences could be found in the two types of MSC. Integrin-mediated signalling seems to play an important role in the generation and maintenance of the chondrocytic phenotype during chondrogenic differentiation. Especially the receptors for fibronectin, vitronectin, osteopontin and collagens might be involved in the generation of the ECM. Intracellularly, their signals might be transduced by ILK and CD47. To fully harness the potential of these cells, future studies should be directed to ascertain their cellular and molecular characteristics for optimal identification, isolation and expansion. 相似文献
916.
Indranil Chatterjee Dr. Sigrid Schmitt Christoph F. Batzilla Susanne Engelmann Andreas Keller Michael W. Ring Ralf Kautenburger Wilma Ziebuhr Michael Hecker Klaus T. Preissner Markus Bischoff Richard A. Proctor Horst P. Beck Hans‐Peter Lenhof Greg A. Somerville Mathias Herrmann 《Proteomics》2009,9(5):1152-1176
Staphylococcus aureus Clp ATPases (molecular chaperones) alter normal physiological functions including an aconitase‐mediated effect on post‐stationary growth, acetate catabolism, and entry into death phase (Chatterjee et al., J. Bacteriol. 2005, 187, 4488–4496). In the present study, the global function of ClpC in physiology, metabolism, and late‐stationary phase survival was examined using DNA microarrays and 2‐D PAGE followed by MALDI‐TOF MS. The results suggest that ClpC is involved in regulating the expression of genes and/or proteins of gluconeogenesis, the pentose‐phosphate pathway, pyruvate metabolism, the electron transport chain, nucleotide metabolism, oxidative stress, metal ion homeostasis, stringent response, and programmed cell death. Thus, one major function of ClpC is balancing late growth phase carbon metabolism. Furthermore, these changes in carbon metabolism result in alterations of the intracellular concentration of free NADH, the amount of cell‐associated iron, and fatty acid metabolism. This study provides strong evidence for ClpC as a critical factor in staphylococcal energy metabolism, stress regulation, and late‐stationary phase survival; therefore, these data provide important insight into the adaptation of S. aureus toward a persister state in chronic infections. 相似文献
917.
918.
Background
Mycobacteria have been shown to contain an apparent redundancy of high-affinity phosphate uptake systems, with two to four copies of such systems encoded in all mycobacterial genomes sequenced to date. In addition, all mycobacteria also contain at least one gene encoding the low-affinity phosphate transporter, Pit. No information is available on a Pit system from a Gram-positive microorganism, and the importance of this system in a background of multiple other phosphate transporters is unclear. 相似文献919.
Melanie Lechner Karin Schmitt Susanne Bauer David Hot Christine Hubans Erwan Levillain Camille Locht Yves Lemoine Roy Gross 《BMC microbiology》2009,9(1):141
Background
Among the members of the genus Bordetella B. petrii is unique, since it is the only species isolated from the environment, while the pathogenic Bordetellae are obligately associated with host organisms. Another feature distinguishing B. petrii from the other sequenced Bordetellae is the presence of a large number of mobile genetic elements including several large genomic regions with typical characteristics of genomic islands collectively known as integrative and conjugative elements (ICEs). These elements mainly encode accessory metabolic factors enabling this bacterium to grow on a large repertoire of aromatic compounds. 相似文献920.
Kati Seidl Susanne Müller Patrice François Carsten Kriebitzsch Jacques Schrenzel Susanne Engelmann Markus Bischoff Brigitte Berger-Bächi 《BMC microbiology》2009,9(1):1-17