Academic literature on the topic 'Protein S'

Protein S (PS) is a vitamin K dependent plasma glycoprotein with multiple functions in coagulation, inflammation and apoptosis. The molecular weight of PS is approximately 70 kDa and its concentration in plasma is about 25 mg/L. In human plasma 40% of PS circulates as free form and the remaining 60% is complexes with complement C4b-binding protein, a component of the complement system. PS circulating in plasma is mainly derived from liver synthesis but, in addition, endothelial cells, testicular Leydig cells and a megakaryocytic cell line (MEG 01) can synthesize PS. Platelet contain PS, but whether this is derived from megakaryocytic synthesis or from uptake of plasma PS by megakaryocyte (Mk) is not known. Free PS acts as a cofactor for activated protein C (APC) in the inactivation of procoagulant factors Va and VIIIa. However, PS also has APC-independent anticoagulant functions, probably through direct inhibition of both the prothrombinase and the tenase complexes. It is hypothesized that intra-platelets PS, release upon platelets stimulation, plays a crucial role in regulating thrombin generation and therefore controlling procoagulant activity. PS deficiency is inherited as an autosomal dominant disordered and is classified in three types: I) reduced plasma levels of total and free PS antigen (PSAg); II) normal concentration of total and free PSAg but with low PS activity; III) low free PSAg; and normal total PSAg. Inherited PS deficiency is generally associated with increased risk of deep venous thrombosis, pulmonary embolism and some cases of arterial thrombosis. The risk of venous thrombosis in PS deficiency increased if 2 associated with other genetic or acquired conditions these includes factor V (FV) Leiden, HR2 aplotype of FV and prothrombin mutation. Several factors influence the concentration of plasma PS, pregnancy, oral contraceptive and oral anticoagulant therapy decreased the levels of PS. To clarify the origin of intra-platelets PS, we development an in vitro model of human megakaryocyte cell culture. Hematopoietic stem cells were isolated by the histopaque system from whole blood of healthy and PS deficiency subjects. Mononuclear cells have been grown in a serum free medium in presence of thrombopoietin (TPO) and interleuchin-3 (IL-3) to stimulate the differentiation into megakaryocytes lineage. The morphology of differentiated mononuclear cells was similar to MKs, and their positive stain with anti-CD41 antibody allowed us to conclude that these cells were indeed Mk. Mk was labeled with ??-tubulin and ?-tubulin antibodies and we observed the cytoplasmatic extensions called proplatelets and the release of platelets. In addition, through immunofluorescence techniques, we detected FV in their cytoplasm whereas protein C was not present as expected. As for PS, it was present in the cytoplasm of MKs obtained from healthy and PS deficiency individuals. Our study demonstrated the PS biosynthesis by megakaryocyte. To study the mechanisms that regulate the concentration of plasma and platelets PS we analyzed plasma and platelets PS from normal and PS deficiency subjects. PS contained in platelets have the same immunoblotting pattern respect to plasma PS. Plasma and platelet PS immunoblotting pattern demonstrated different molecular weight of PS in some deficient PS individuals as compared to normal control, suggesting different mutations in PS gene. We analyzed the presence of mutation and the presence of PS Heerlen allele. We investigated platelets PS antigen levels in type I and type III PS deficient patients. In type I subjects total and plasma free PS antigen levels were (PSAg) 62±7% and 37±12% 3 respectively. In carries of type III defect total and free PSAg levels were 85±13% and 41±13% respectively. Platelets PSAg in type I and type III were 66 ±32% and 80±37%.In a subgroup of healthy individuals total, free and platelet PSAg levels were 119±17%, 110±17% and 101±30%, respectively. The results indicate that type I and III subject’s total and plasma free PSAg levels were lower than normal individuals. Intra-platelets PSAg levels in type I and type III were lower than of healthy individuals. Our analysis demonstrates a strict correlation between total and free plasma PS and Plts PS. The reduction of platelet PS mirrors the reduced levels of free and total PSAg present in carries of the defect even though PS levels in Plts appears unexpectedly higher than the free PS counterpart. Moreover, we study the interaction of anticoagulant drugs on PSAg levels on 35 patient treatments with warfarin. The levels of total and free plasma PS decreased during treatment with oral anticoagulant, since PS is a vitamin K-dependent protein. Our study demonstrated significant decreased levels of platelet PS respectively plasma free and total PS. We valuated the effect of anticoagulant drugs (warfarin) and of vitamin K on Mk cells. The Mk were treatment with 1?g/ml of warfarin or 1?g/ml of vitamin K and analyze synthesis of PS. We observed decreased PS synthesis on MKs with warfarin than control MKs; on the contrary, MKs cultured under vitamin K treatment increase PS synthesis.<br>La proteina S (PS) è una glicoproteina plasmatica, vitamina K-dipendente, con molteplici funzioni nell’ambito della coagulazione, infiammazione e apoptosi. Il suo peso molecolare è di 70 kDa e la sua concentrazione plasmatica di circa 25 mg/L. Nel plasma umano il 40% della PS circola in forma libera, mentre il restante 60% è legato alla C4b-binding-protein, una proteina del sistema del complemento. La PS circolante nel plasma viene sintetizzata principalmente nel fegato ma anche le cellule endoteliali, le cellule di Leydig e una linea cellulare di megacariociti sono in grado di sintetizzarla. Le piastrine contengono PS, anche se la sua origine non è ancora stata chiarita. Si ipotizza che derivi dalla sintesi dei megacariociti o che siano gli stessi megacariociti ad assumerla dal pool plasmatico mediante un meccanismo di endocitosi. La PS libera agisce da cofattore per la proteina C attivata (APC) nell’inattivazione dei fattori procoagulanti Va (FVa ) e VIIIa (FVIIIa). La PS esercita anche un’azione anticoagulante APC-indipendente, probabilmente inibendo direttamente i complessi tenase e protrombinase. Si suppone che la PS rilasciata dalle piastrine in seguito alla loro attivazione regoli la generazione di trombina, controllando perciò l’attività procoagulante. I difetti di PS sono a trasmissione autosomica dominante e vengono classificati in tre tipi: – difetto di tipo I, caratterizzato da ridotti livelli plasmatici di PS totale e libera; – difetto di tipo II, caratterizzato da livelli fisiologici di PS totale e libera associati ad una ridotta attività; 6 – difetto di tipo III, presenta una PS libera ridotta ed una PS totale nella norma. I difetti di PS sono generalmente associati ad un aumentato rischio di trombosi venosa profonda, embolismo polmonare ed, in qualche caso, a trombosi arteriosa. Nei deficit di PS il rischio di trombosi venosa aumenta se associato ad altre condizioni di carattere genetico o acquisito quali il FV Leiden, l’aplotipo HR2 del FV e mutazioni a carico del gene che codifica per la protrombina. Molteplici fattori, tra cui la gravidanza, la terapia anticoncezionale e anticoagulante orale, riducono la concentrazione plasmatica della PS. Al fine di chiarire l’origine della PS piastrinica, abbiamo messo a punto un modello in vitro di colture di megacariociti umani. Le cellule staminali ematopoietiche sono state isolate con histopaque da sangue intero di soggetti sani e con difetto di PS. Le cellule mononucleate sono state coltivate in un terreno privo di siero ed in presenza di trombopoietina (TPO) e interleuchina 3 (IL3) per stimolarne la differenziazione in una linea magacariocitaria. Le cellule mononucleate differenziate presentavano una morfologia simile a quella dei megacariociti e risultavano positive all’anticorpo anti-CD41; questi elementi ci hanno permesso di confermare che si trattasse effettivamente di megacariociti. Inoltre, la marcatura dei megacariociti con anticorpi anti ??-tubulina e ?-tubulina ha evidenziato sia la presenza di estensioni citoplasmatiche denominate “proplatelets” sia il rilascio di piastrine da parte dei megacariociti. In aggiunta, mediante tecniche di immunofluorescenza, abbiamo rilevato la presenza del FV a livello citoplasmatico, mentre la PC era assente. La PS era presente nel citoplasma dei megacariociti isolati da individui sani e con difetto di PS. La nostra ricerca ha così dimostrato la sintesi di PS da parte dei megacariociti. 7 Per studiare il meccanismo che regola i livelli di PS presenti nel plasma e all’interno delle piastrine, abbiamo determinato la concentrazione di PS plasmatica e piastrinica in soggetti sani e portatori di difetto di PS. La PS piastrinica mostrava lo stesso pattern elettroforetico di quella isolata dal plasma. L’analisi immunologica ha inoltre evidenziato, per alcuni soggetti portatori del difetto, una PS plasmatica con differente peso molecolare rispetto ai controlli sani; questo ci ha suggerito la presenza di mutazioni nel gene della PS. Abbiamo quindi testato la presenza di eventuali mutazioni e dell’allele Heerlen. In soggetti portatori di difetto di PS di tipo I i livelli di PS totale plasmatici, e libera erano: 62±7% e 37±12% . In soggetti portatori di difetto di PS di tipo III i livelli di PS totale e libera nel plasma erano di 85±13% e 41±13%. I livelli di PS nelle piastrine nei soggetti portatori di difetto di PS di tipo I e di tipo III erano di 66 ±32% e 80±37%. In un gruppo di persone sane i livelli di PS totale, libera e piastrinica erano di 119±17%, 110±17% e 101±30%, rispettivamente. Dall’analisi dei livelli plasmatici e piastrinici di PS in soggetti portatori del difetto di tipo I e III è emerso che a) nei pazienti con difetto i livelli di PS totale e libera erano più bassi rispetto ai soggetti sani; b) i pazienti con difetto presentavano livelli di PS piastrinica ridotti rispetto agli individui sani utilizzati come controllo. La nostra analisi ha dimostrato una stretta correlazione tra la PS plasmatica (libera e totale) e quella piastrinica. La diminuzione della concentrazione di PS piastrinica, osservata negli individui portatori del difetto, riflette l’abbassamento del livello di PS plasmatica, sebbene la quota di PS all’interno delle piastrine risulti maggiore rispetto a quella della PS presente nel plasma in forma libera. In seguito abbiamo studiato l’effetto di sostanze anticoagulanti sui livelli plasmatici e piastrinici di PS in pazienti 8 sani in trattamento con warfarina. E’ noto che la warfarina abbassa i livelli plasmatici di PS in quanto quest’ultima è una proteina vitamina Kdipendente. Anche i livelli di PS plasmatica, (totale e libera), e piastrinica dei medesimi soggetti in terapia con warfarina risultano ridotti rispetto alla norma ma l’abbassamento della concentrazione di PS appare molto più marcata all’interno delle piastrine piuttosto che nel plasma. Infine abbiamo valutato l’effetto della warfarina e della vitamina K sulla sintesi di PS da parte dei megacariociti. Mediante tecniche di immunofluorescenza abbiamo osservato una ridotta sintesi della PS nei megacariociti trattati con warfarina rispetto alle cellule di controllo; al contrario, i megacariociti coltivati in un terreno supplementato con vitamina K mostravano un incremento della sintesi di PS.

DNA damage can lead to the accumulation of mutations and diseases such as cancer. It is therefore integral for cells to identify this damaged DNA and promote its repair. To carry out this function eukaryotic cells have evolved signal transduction pathways known as the DNA structure checkpoints. Much of the molecular mechanism underlying these pathways is still far from understood. The work in this thesis uses the model organism Schizosaccharomyces pombe to investigate these mechanisms, with a particular focus on the TopBP1 homolog Rad4. TopBP1 plays an essential scaffolding role in the initiation of DNA replication, but is also a key protein in the DNA structure checkpoints. It has previously been shown in metazoans and budding yeast to stimulate the kinase activity of ATR, via its ATR Activation Domain (AAD), an early event in checkpoint activation. The work presented in here, along with initial work carried by previous members of the Carr Laboratory; Su-Jiun Lin and Valerie Garcia, shows that the Rad4TopBP1 AAD acts in a chromatin dependent pathway to amplify the checkpoint signal in G1/S-phase, where DNA resection is limited. A second AAD is also identified in the checkpoint clamp protein Rad9, which acts redundantly with the Rad4 AAD. As well as its AAD function, Rad4 also plays a scaffolding role in the DNA structure checkpoint pathways. The work in this thesis, in collaboration with the Laurence Pearl and Li Lin Du laboratories, identifies the molecular mechanism of the interaction between Rad4 and the mediator protein Crb253BP1. It is shown that sequential phosphorylation of Crb2 by Cdc2CDK is required for the interaction with BRCT domains 1 and 2 of Rad4 and checkpoint activation. It is also shown that Rad4 most likely does not interact with Mrc1 or Slx4 in the S. pombe checkpoint pathways.

Palmitoylation refers to the covalent attachment of fatty acids, such as palmitate, onto the cysteine residues of proteins. This process may subsequently alter their localization and function. Nearly all of the enzymes that catalyze palmitoylation, zDHHC protein acyl transferases (PATs), are implicated in neurological disorders, infectious diseases, and cancer in humans. Of particular interest to those who study palmitoylation are Ras family GTPas and zDHHC9-GCP16, the zDHHC PAT that palmitoylates Ras proteins. Erf2-Erf4 is the zDHHC PAT that palmitoylates Ras proteins in Saccharomyces cerevisiae. Currently, there are no methods to therapeutically target palmitoylation for the treatment of disease. One of the barriers to identifying a modulator of palmitoylation is the lack of a reliable high-throughput screening system. To date, few assay systems have been developed to examine the kinetics and mechanism of that palmitoylation reaction. This lab has developed a fluorescence-based coupled assay to gain insight into the enzymology, biochemical mechanism, and kinetics of the palmitoylation reaction. This assay may be used to identify specific inhibitors of autopalmitoylation. In the first step of this reaction, the palmitoyl-moiety from palmitoyl-CoA is transferred to the zDHHC9 PAT cysteine side chain to form a palmitoyl:enzyme intermediate. The second step of palmitoylation is the subsequent transfer of the palmitoyl-moiety from the palmitoyl:enzyme intermediate to the cysteine residue of the substrate protein. This fluorescence-based coupled assay was utilized to screen a natural products library and a unique synthetic compound library for inhibitors of Erf2 autopalmitoylation. These screens led to the identification of fungal metabolite extracts and ten bis-cyclic piperazine compounds that inhibit Erf2 autopalmitoylation in the low micromolar range. This effect is similar to known inhibitors of palmitoylation that lack specificity for the palmitoylation reaction itself.

[Truncated abstract] Every year thousands of individuals suffer from thrombotic related complications that in some cases can be fatal and every year millions of women take some form of hormonal contraceptive. In some cases, there is a cause and effect relationship between the two as users of the combined oral contraceptive pill have an increased risk of developing a thrombotic event. Increased circulating levels of oestrogen cause a prothrombotic shift in the coagulation cascade resulting from upregulation of several procoagulant proteins and a decrease of key anticoagulant proteins. One of the most oestrogen sensitive anticoagulants is Protein S (PS), a product of the PROS1 gene. PS acts as a cofactor to activated protein C (aPC) and the PS-aPC complex serves to downregulate clot formation by deactivating the tenase and prothrombinase complexes via proteolytic cleavage of activated factors VIII and V, respectively. As such, low PS levels are associated with an increased risk of developing thrombotic disorders such as pulmonary embolism, stroke or coronary thrombosis and deep vein thrombosis. During pregnancy when oestrogen levels increase, a steady decline in PS is evident in the early weeks of gestation and continues to decrease to below the normal range in the 2nd trimester, remaining there until post-partum. In addition, reduced free and total PS levels are observed in users of the combined oral contraceptive (COC) pill that contains an oestrogen and a progestin. Interestingly, users of 3rd generation COCs have significantly greater reductions of PS than do 2nd generation COC users. The difference between the two forms is the type of progestin, not the oestrogen, which is predominantly ethinyl oestradiol in the majority of commercially available preparations. At present, a mechanism to describe the relationship between oestrogen and/or progesterone associated with the observed in vivo changes in the levels of PS has not been identified. The aim of this thesis was to define the molecular mechanisms involved in the regulation of PS expression by oestrogen and progesterone. In this study, a Combined Single-stranded conformational analysis and Heteroduplex Analysis (CSHA) iv methodology was optimised for screening both PROS1 DNA and mRNA for the detection of mutations. '...' This may explain why users of 3rd generation COCs display a greater reduction in circulating PS levels compared to 2nd generation users. To investigate potential PS interactions with other proteins that could be hormonally regulated, a yeast-2-hybrid (Y-2-H) screen was performed using the PS molecule as a 'bait' against molecules derived from liver and bone marrow cDNA libraries. A clone that contained a portion of another haemostatic protein, Protein Z (PZ) was isolated and confirmed via sequencing. As no full length PZ clones were identified, a second Y-2-H screen was performed once again using the PS molecule as bait and the PZ molecule as the fish. Interaction between the two proteins was shown to be possible via the successful growth of colonies on triple knock out selective media and by positive ß-galactosidase activity.

This dissertation is a study in how heme facilitates biology using two heme proteins as examples. I write about my mechanistic studies on Cimex nitrophorin and preliminary studies on Ecdysone inducible protein 75, respectively. Nitrophorins are salivary heme proteins used by bloodfeeding insects to deliver NO to the victim, leading to vasodilation and antihemostasis. The bedbug nitrophorin cNP, a thiolate heme protein accomplishes this via an unusual heme-assisted S-nitrosation reaction, requiring proximal ligand cleavage. This dissertation explores this mechanism through mutational, crystallographic and transient kinetic approaches. I present the detailed investigation of the two NO binding events, one at the heme and the other at the proximal cysteine. The heme nitrosyl shows marked pH dependence arising out of the apparent protonation of the proximal cysteine ligand, a feature crucial to cNP function. The structures and spectroscopy of cNP mutant proteins reveal the SNO modification to be regulatory in nature. Laser flash photolysis measurements and the structures of mutant proteins reveal the negative influence of steric hindrance on SNO stability.Studies of insect embryogenesis and metamorphosis reveal the regulatory role of the hormone ecdysone via its target, the ecdysone receptor. Ecdysone triggers expression of several nuclear receptors in a time and tissue dependant fashion, which in turn carry out gene regulation. Ecdysone inducible protein 75 (E75), a nuclear receptor and an early ecdysone responsive gene product, regulates a subset of the developmental activities attributed to ecdysone. We are investigating E75 from Aedes aegypti to uncover its role in ecdysone signaling in mosquitoes. I have expressed and partially purified the full length protein using the baculovirus driven expression in SF9 cells, and purified to homogeneity the heme binding domain resolubilized from inclusion bodies obtained by expression in E. coli. Preliminary characterization of the proteins using UV-visible spectroscopy indicates that E75 has a b type heme with a low spin six-coordinate ferric iron. In the E75 heme binding domain, the heme exhibits an unstable ferrous state and only binds NO and CO at high non-physiological levels. These data place into doubt the suggested roles for E75 as a gas regulated transcription regulator.