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81.
82.
Tyrosine hydroxylase's catalysis of tyrosine to dihydroxyphenylalanine (DOPA) is the highly regulated, rate-limiting step
catalyzing the synthesis of the catecholamine neurotransmitter dopamine. Phosphorylation, cofactor-mediated regulation, and
the cell's redox status, have been shown to regulate the enzyme's activity. This paper incorporates these regulatory mechanisms
into an integrated dynamic model that is capable of demonstrating relative rates of dopamine synthesis under various physiological
conditions. Most of the kinetic equations and substrate parameters used in the model correspond with published experimental
data, while a few which were not available in literature have been optimized based on explicit assumptions. This kinetic pathway
model permits a comparison of the relative regulatory contributions made by variations in substrate, phosphorylation, and
redox status on enzymatic activity and permits predictions of potential disease states. For example, the model correctly predicts
the recent observation that individuals with haemochromatosis and having excessive iron accumulation are at increased risk
for acquiring Parkinsonism, a defect in neuronal dopamine synthesis (Bartzokis et al., 2004; Costello et al., 2004). Alpha
synuclein mediated regulation of tyrosine hydroxylase has also been incorporated in the model, allowing an insight into the
over-expression and aggregation of alpha synuclein in Parkinson's disease.
Action Editor: Upinder Bhalla 相似文献
83.
Yoshihito Ishida Akitsugu Yamamoto Akira Kitamura Shireen R. Lamand Tamotsu Yoshimori John F. Bateman Hiroshi Kubota Kazuhiro Nagata 《Molecular biology of the cell》2009,20(11):2744-2754
Type I collagen is a major component of the extracellular matrix, and mutations in the collagen gene cause several matrix-associated diseases. These mutant procollagens are misfolded and often aggregated in the endoplasmic reticulum (ER). Although the misfolded procollagens are potentially toxic to the cell, little is known about how they are eliminated from the ER. Here, we show that procollagen that can initially trimerize but then aggregates in the ER are eliminated by an autophagy-lysosome pathway, but not by the ER-associated degradation (ERAD) pathway. Inhibition of autophagy by specific inhibitors or RNAi-mediated knockdown of an autophagy-related gene significantly stimulated accumulation of aggregated procollagen trimers in the ER, and activation of autophagy with rapamycin resulted in reduced amount of aggregates. In contrast, a mutant procollagen which has a compromised ability to form trimers was degraded by ERAD. Moreover, we found that autophagy plays an essential role in protecting cells against the toxicity of the ERAD-inefficient procollagen aggregates. The autophagic elimination of aggregated procollagen occurs independently of the ERAD system. These results indicate that autophagy is a final cell protection strategy deployed against ER-accumulated cytotoxic aggregates that are not able to be removed by ERAD. 相似文献
84.
85.
Justin M. Allen Laura Zamurs Bent Brachvogel Ursula Schl?tzer-Schrehardt Uwe Hansen Shireen R. Lamandé Lynn Rowley Jamie Fitzgerald John F. Bateman 《The Journal of biological chemistry》2009,284(18):12020-12030
WARP is a recently identified extracellular matrix molecule with restricted
expression in permanent cartilages and a distinct subset of basement membranes
in peripheral nerves, muscle, and the central nervous system vasculature. WARP
interacts with perlecan, and we also demonstrate here that WARP binds type VI
collagen, suggesting a function in bridging connective tissue structures. To
understand the in vivo function of WARP, we generated a
WARP-deficient mouse strain. WARP-null mice were healthy, viable, and fertile
with no overt abnormalities. Motor function and behavioral testing
demonstrated that WARP-null mice exhibited a significantly delayed response to
acute painful stimulus and impaired fine motor coordination, although general
motor function was not affected, suggesting compromised peripheral nerve
function. Immunostaining of WARP-interacting ligands demonstrated that the
collagen VI microfibrillar matrix was severely reduced and mislocalized in
peripheral nerves of WARP-null mice. Further ultrastructural analysis revealed
reduced fibrillar collagen deposition within the peripheral nerve
extracellular matrix and abnormal partial fusing of adjacent Schwann cell
basement membranes, suggesting an important function for WARP in stabilizing
the association of the collagenous interstitial matrix with the Schwann cell
basement membrane. In contrast, other WARP-deficient tissues such as articular
cartilage, intervertebral discs, and skeletal muscle showed no detectable
abnormalities, and basement membranes formed normally. Our data demonstrate
that although WARP is not essential for basement membrane formation or
musculoskeletal development, it has critical roles in the structure and
function of peripheral nerves.WARP (von Willebrand A domain-related
protein) is a recently described member of the von Willebrand
factor type A domain
(VWA2 domain)
superfamily of extracellular matrix (ECM) molecules, adhesion proteins, and
cell surface receptors (for review, see Ref.
1). The WARP protein is encoded
by the Vwa1 (von Willebrand factor A
domain-containing 1) gene and comprises a single N-terminal VWA
domain containing a putative metal ion-dependent adhesion site (MIDAS) motif,
two fibronectin type III repeats, and a unique C-terminal domain that
contributes to WARP multimer formation
(2,
3). Like many other VWA
domain-containing extracellular molecules, WARP was predicted to participate
in protein-protein interactions and in the formation of supramolecular
structures. Recently WARP has been shown to interact with the heparan sulfate
proteoglycan perlecan (3), and
in the present study we identify type VI collagen as a ligand for WARP.WARP has a restricted distribution in developing cartilage tissues, where
it is expressed at sites of joint cavitation and articular cartilage formation
rather than cartilage structures that will undergo endochondral ossification
(3). In adult tissues, WARP is
highly restricted to the chondrocyte pericellular matrix in articular
cartilage and fibrocartilages, where it co-localizes with perlecan and
collagen VI (3). Several of the
major basement membrane components have been found in the chondrocyte
pericellular matrix, suggesting that this structure may be the functional
equivalent of a basement membrane in cartilage tissues
(4). Consistent with this
hypothesis, recent data from our laboratory have demonstrated that WARP is a
component of the basement membrane in a limited subset of tissues including
the apical ectodermal ridge, the endomysium surrounding muscle fibers, the
vasculature of the central nervous system, and the endoneurium of peripheral
nerves (5). The principal
components of basement membranes are type IV collagen, laminins, nidogens, and
proteoglycans including perlecan; however, the composition, structure, and
biological properties of basement membranes can differ considerably between
different tissues (6,
7). Different isoforms of the
major components contribute to the heterogeneity of basement membranes, but
the contribution of quantitatively minor components to particular subtypes of
basement membranes and their interactions with surrounding cells and ECM
structures are poorly understood
(8,
9).We, therefore, have generated mice with a targeted disruption of the WARP
locus to determine the consequences of WARP deficiency on skeletal development
and basement membrane formation. The homozygous null mice are viable, fertile,
and do not exhibit overt abnormalities compared with wild type littermates.
Neurological testing revealed that WARP-null mice exhibit a delayed response
to acute painful stimulus and a disturbance in fine motor coordination,
although general motor function is not impaired. Consistent with these
findings, immunohistochemical analysis of peripheral nerves from WARP-null
mice revealed that the collagen VI microfibrillar matrix was severely reduced
and mislocalized compared with wild type mice. Furthermore, electron
microscopic examination of the sciatic nerve demonstrated a reduction in the
collagen I ECM and the unusual partial fusing of the basement membranes of
neighboring axons. These data suggest an important role for WARP in organizing
the peripheral nerve ECM and provides evidence for tissue-specific differences
in the role of WARP in the assembly and/or integration of the ECM. In
addition, our studies provide further evidence for the critical role of ECM
structure and organization in nerve function. 相似文献
86.
Leona D. Tooley Laura K. Zamurs Nicola Beecher Naomi L. Baker Rachel A. Peat Naomi E. Adams John F. Bateman Kathryn N. North Clair Baldock Shireen R. Lamandé 《The Journal of biological chemistry》2010,285(43):33567-33576
Collagen VI is an extracellular protein that most often contains the three genetically distinct polypeptide chains, α1(VI), α2(VI), and α3(VI), although three recently identified chains, α4(VI), α5(VI), and α6(VI), may replace α3(VI) in some situations. Each chain has a triple helix flanked by N- and C-terminal globular domains that share homology with the von Willebrand factor type A (VWA) domains. During biosynthesis, the three chains come together to form triple helical monomers, which then assemble into dimers and tetramers. Tetramers are secreted from the cell and align end-to-end to form microfibrils. The precise molecular mechanisms responsible for assembly are unclear. Mutations in the three collagen VI genes can disrupt collagen VI biosynthesis and matrix organization and are the cause of the inherited disorders Bethlem myopathy and Ullrich congenital muscular dystrophy. We have identified a Ullrich congenital muscular dystrophy patient with compound heterozygous mutations in α2(VI). The first mutation causes skipping of exon 24, and the mRNA is degraded by nonsense-mediated decay. The second mutation is a two-amino acid deletion in the C1 VWA domain. Recombinant C1 domains containing the deletion are insoluble and retained intracellularly, indicating that the mutation has detrimental effects on domain folding and structure. Despite this, mutant α2(VI) chains retain the ability to associate into monomers, dimers, and tetramers. However, we show that secreted mutant tetramers containing structurally abnormal C1 VWA domains are unable to associate further into microfibrils, directly demonstrating the critical importance of a correctly folded α2(VI) C1 domain in microfibril formation. 相似文献
87.
Hsp90 is an ATP-dependent molecular chaperone that regulates key signaling proteins and thereby impacts cell growth and development.
Chaperone cycle of Hsp90 is regulated by ATP binding and hydrolysis through its intrinsic ATPase activities, which is in turn
modulated by interaction with its co-chaperones. Hsp90 ATPase activity varies in different organisms and is known to be increased
in tumor cells. In this study we have quantitatively analyzed the impact of increasing Hsp90 ATPase activity on the activities
of its clients through a virtual prototyping technology, which comprises a dynamic model of Hsp90 interaction with clients
involved in proliferation pathways. Our studies highlight the importance of increased ATPase activity of Hsp90 in cancer cells
as the key modulator for increased proliferation and survival. A tenfold increase in ATPase activity of Hsp90 often seen in
cancer cells increases the levels of active client proteins such as Akt-1, Raf-1 and Cyclin D1 amongst others to about 12-,
8- and 186-folds respectively. Additionally we studied the effect of a competitive inhibitor of Hsp90 activity on the reduction
in the client protein levels. Virtual prototyping experiments corroborate with findings that the drug has almost 10- to 100-fold
higher affinity as indicated by a lower IC50 value (30–100 nM) in tumor cells with higher ATPase activity. The results also indicate a 15- to 25-fold higher efficacy
of the inhibitor in reducing client levels in tumor cells. This analysis provides mechanistic insights into the links between
increased Hsp90 ATPase activity, tumor phenotype and the hypersensitivity of tumor Hsp90 to inhibition by ATP analogs. 相似文献
88.
Ozlem Equils Priya Nambiar Calvin J. Hobel Roger Smith Charles F. Simmons Shireen Vali 《PloS one》2010,5(1)
Background
Sufficient information from in vitro and in vivo studies has become available to permit computer modeling of the processes that occur in the myometrium during labor. This development allows the in silico investigation of pathological mechanisms and the trialing of potential treatments.Methods/Results
Based on the human literature, we developed a computer model of the immune-endocrine environment of the myometrial cell. The interactions between molecules are represented by differential equations. The model is designed to simulate the estrogen and progesterone receptor changes during pregnancy and particularly the changes in the progesterone receptor (PR) isoforms A and B that are thought to mediate functional progesterone withdrawal in the human at labor. Parturition is represented by an increase in the PRA to PRB ratio to levels seen in women in labor. Infection is shown by inducing inflammation in the system by increasing phospho-IkB kinase concentration (IKK) levels; which lead to increased NF-κB activation, causing an increase in the PRA/PRB ratio. We examined the effects of progesterone or cyclo-oxygenase 2 (Cox2) inhibitor treatments on the PRA/PRB ratio in silico. The model predicted that high doses of progesterone and Cox2 inhibition would be effective in preventing an NF-κB-induced PRA/PRB ratio increase to the levels found during labor.Conclusions
Our data illustrate the use of dynamic biological computer simulations to test the effectiveness of therapeutic interventions. This may allow the early rejection of ineffective therapies prior to expensive field trials. 相似文献89.
90.
Melody McConnell Sujan Mamidi Rian Lee Shireen Chikara Monica Rossi Roberto Papa Phillip McClean 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2010,121(6):1103-1116
Molecular linkage maps are an important tool for gene discovery and cloning, crop improvement, further genetic studies, studies
on diversity and evolutionary history, and cross-species comparisons. Linkage maps differ in both the type of marker and type
of population used. In this study, gene-based markers were used for mapping in a recombinant inbred (RI) population of Phaseolus vulgaris L. P. vulgaris, common dry bean, is an important food source, economic product, and model organism for the legumes. Gene-based markers were
developed that corresponded to genes controlling mutant phenotypes in Arabidopsis thaliana, genes undergoing selection during domestication in maize, and genes that function in a biochemical pathway in A. thaliana. Sequence information, including introns and 3′ UTR, was generated for over 550 genes in the two genotypes of P. vulgaris. Over 1,800 single nucleotide polymorphisms and indels were found, 300 of which were screened in the RI population. The resulting
LOD 2.0 map is 1,545 cM in length and consists of 275 gene-based and previously mapped core markers. An additional 153 markers
that mapped at LOD <1.0 were placed in genetic bins. By screening the parents of other mapping populations, it was determined
that the markers were useful for other common Mesoamerican × Andean mapping populations. The location of the mapped genes
relative to their homologs in Arabidopsis thaliana (At), Medicago truncatula (Mt), and Lotus japonicus (Lj) were determine by using a tblastx analysis with the current pseduochromosome builds for each of the species. While only
short blocks of synteny were observed with At, large-scale macrosyntenic blocks were observed with Mt and Lj. By using Mt
and Lj as bridging species, the syntenic relationship between the common bean and peanut was inferred. 相似文献