Epidemiology and impact of frailty in patients with atrial fibrillation in Europe

BACKGROUND

Frailty is a medical syndrome characterised by reduced physiological reserve and increased vulnerability to stressors. Data regarding the relationship between frailty and atrial fibrillation (AF) are still inconsistent.

OBJECTIVES

We aim to perform a comprehensive evaluation of frailty in a large European cohort of AF patients.

METHODS

A 40-item frailty index (FI) was built according to the accumulation of deficits model in the AF patients enrolled in the ESC-EHRA EORP-AF General Long-Term Registry. Association of baseline characteristics, clinical management, quality of life, healthcare resources use and risk of outcomes with frailty was examined.

RESULTS

Among 10,177 patients [mean age (standard deviation) 69.0 (11.4) years, 4,103 (40.3%) females], 6,066 (59.6%) were pre-frail and 2,172 (21.3%) were frail, whereas only 1,939 (19.1%) were considered robust. Baseline thromboembolic and bleeding risks were independently associated with increasing FI. Frail patients with AF were less likely to be treated with oral anticoagulants (OACs) (odds ratio 0.70, 95% confidence interval 0.55-0.89), especially with non-vitamin K antagonist OACs and managed with a rhythm control strategy, compared with robust patients. Increasing frailty was associated with a higher risk for all outcomes examined, with a non-linear exponential relationship. The use of OAC was associated with a lower risk of outcomes, except in patients with very/extremely high frailty.

CONCLUSIONS

In this large cohort of AF patients, there was a high burden of frailty, influencing clinical management and risk of adverse outcomes. The clinical benefit of OAC is maintained in patients with high frailty, but not in very high/extremely frail ones.

Abstract P1-09-01: The effect of generic anastrozole on adherence to adjuvant endocrine therapy

Background: Endocrine therapies, particularly aromatase inhibitors, substantially reduce breast cancer mortality in clinical trials. High rates of cost-related nonadherence to these long-term oral medications, however, have reduced their population-wide impact. While the 2006 Medicare Part D introduction promised to improve this situation, most Part D enrollees’ out-of pocket aromatase inhibitor costs actually remained high and rose steadily over subsequent years. We examined the effect of a natural experiment which lowered these costs—anastrozole patent expiration—upon endocrine therapy adherence among a nationwide sample of breast cancer patients.

Methods:Our sample included all female Medicare beneficiaries aged > = 66 identified (using a validated Medicare claims algorithm) as having incident breast cancer surgery in 2006-07 who also had one or more Part D claim for an aromatase inhibitor or tamoxifen between 7/1-12/30/2008. Part D claims were used to calculate adherence, defined as medication possession ratio (MPR)>80%, and medication out-of-pocket costs. A binary outcome regression model with a logit link was estimated using generalized estimating equations to study the effect of FDA approval of generic anastrozole (7/1/2010) upon adherence. The model was also adjusted for patient sociodemographic and health characteristics (age, race, comorbidities), time since surgery, low-income subsidy (LIS) (which lowers copays and eliminates the Medicare D “donut hole”) and temporal trend.

Results: The mean out-of-pocket medication cost for the 22,203 cohort members (85% white, 47% age > = 75, 31% low income subsidy recipients, 45% anastrozole users) was $205 in the first quarter of 2009. Cohort members’ adherence to endocrine therapies dropped 15.8% from 72% in the first quarter to 61% in the last quarter during the pre-generic year (2009). In contrast, adherence was reduced by less than half that amount (-6.3%) between the same time periods in 2010 once anastrozole went generic. In adjusted models, both generic anastrozole availability and receipt of a low income subsidy were strongly associated with greater adherence to hormonal therapy (table). White race, younger age, and lower comorbidity all had smaller but statistically significant associations with greater adherence. There were no significant interactions between variables.

Adherence to Adjuvant Endocrine Therapy with Availability of Generic AnastrozoleFactorOdds Ratio95 CIP valueGeneric Anastrozole2.642.38 to 2.94.001Low Income Subsidy1.961.76 to 2.20.001also adjusted for year, quarter of year, comorbidity, race, age

Conclusions and Implications: The introduction of generic anastrozole was associated with a substantial and clinically significant improvement in endocrine therapy adherence among Medicare Part D enrollees. Such results have generally not been observed in studies of generic medications for chronic diseases, and may partly reflect increasing out-of-pocket demands by insurers. These findings, along with our findings of better adherence among low income subsidy recipients, highlight the importance of regulatory and subsidy policies for patients requiring long-term cancer medications.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-09-01.

CBX3 regulates efficient RNA processing genome-wide

CBX5, CBX1, and CBX3 (HP1α, β, and γ, respectively) play an evolutionarily conserved role in the formation and maintenance of heterochromatin. In addition, CBX5, CBX1, and CBX3 may also participate in transcriptional regulation of genes. Recently, CBX3 binding to the bodies of a subset of genes has been observed in human and murine cells. However, the generality of this phenomenon and the role CBX3 may play in this context are unknown. Genome-wide localization analysis reveals CBX3 binding at genic regions, which strongly correlates with gene activity across multiple cell types. Depletion of CBX3 resulted in down-regulation of a subset of target genes. Loss of CBX3 binding leads to a more dramatic accumulation of unspliced nascent transcripts. In addition, we observed defective recruitment of splicing factors, including SNRNP70, to CBX3 target genes. Collectively, our data suggest a role for CBX3 in aiding in efficient cotranscriptional RNA processing.

Conserved antagonism between JMJD2A/KDM4A and HP1γ during cell cycle progression

The KDM4/JMJD2 family of histone demethylases is amplified in human cancers. However, little is known about their physiologic or tumorigenic roles. We have identified a conserved and unappreciated role for the JMJD2A/KDM4A H3K9/36 tridemethylase in cell cycle progression. We demonstrate that JMJD2A protein levels are regulated in a cell cycle-dependent manner and that JMJD2A overexpression increased chromatin accessibility, S phase progression, and altered replication timing of specific genomic loci. These phenotypes depended on JMJD2A enzymatic activity. Strikingly, depletion of the only C. elegans homolog, JMJD-2, slowed DNA replication and increased ATR/p53-dependent apoptosis. Importantly, overexpression of HP1γ antagonized JMJD2A-dependent progression through S phase, and depletion of HPL-2 rescued the DNA replication-related phenotypes in jmjd-2(-/-) animals. Our findings describe a highly conserved model whereby JMJD2A regulates DNA replication by antagonizing HP1γ and controlling chromatin accessibility.

Individualised assessment of response to clopidogrel in patients presenting with acute coronary syndromes: a role for short thrombelastography?

INTRODUCTION

There is considerable interindividual variation in response to the antiplatelet agent clopidogrel. Hyporesponse predicts negative outcomes in patients presenting with a variety of ischemic cardiac conditions and following intracoronary stent placement. Many tests of clopidogrel activity are time consuming and complex. Short thromboelastography (s-TEG) allows rapid measurement of platelet clopidogrel response.

AIMS

We initiated this study to investigate the utility of s-TEG in assessing the response to clopidogrel in patients presenting with acute coronary syndromes (ACS) and to compare these results with established clopidogrel monitoring techniques.

METHODS

Patients admitted with unstable angina (UA) or Non ST elevation myocardial infarction (NSTEMI) undergoing coronary angiography were recruited. After routine loading with clopidogrel, all patients were tested with s-TEG and Accumetrics Verify-Now rapid platelet function analyzer (VN-RPFA). We used the modified TEG technique of measuring area under the curve at 15 min (AUC15), which allows a rapid estimation of antiplatelet response. Vasodilator-stimulated phosphoprotein phosphorylation (VASP) was also tested in a subgroup of patients. Clinical follow-up was obtained at 1 year. s-TEG results were correlated with VN-RPFA and VASP findings.

RESULTS

A total of 49 patients (33 male, mean age 63) were recruited and tested with s-TEG and VN-RPFA and a total of 39 patients were also assessed with VASP. s-TEG readings correlated well with VN-RPFA (r(2)= 0.54, P < 0.0001) and VASP (r(2)= 0.26, P= 0.001).

CONCLUSION

s-TEG provides timely results which compare to current tests of clopidogrel activity. This technique can also be used to measure a variety of other clotting parameters and as such could develop into a valuable near patient test for the interventional cardiologist.

HP1-mediated silencing targets Pol II coactivator complexes

Little is known of the specific biochemical mechanism by which heterochromatin protein 1 (HP1) inactivates a gene. We analyzed HP1-mediated inhibition of preinitiation complex (PIC) assembly in vitro on chromatin templates regulated by GAL4-VP16 or Sp1. HP1 blocked key subunits of the TFIID and Mediator coactivator complexes. Notably, binding of the same subunits was inhibited by HP1 on the Sp1-regulated survivin gene in vivo upon DNA damage-induced silencing.

Functional cooperation between HP1 and DNMT1 mediates gene silencing

Mammalian euchromatic gene silencing results from the combined repressive effects of histone and DNA methyltransferases. Little is known of the mechanism by which these enzymes cooperate to induce silencing. Here we show that mammalian HP1 family members mediate communication between histone and DNA methyltransferases. In vitro, methylation of histone 3 Lys 9 by G9a creates a binding platform for HP1alpha, beta, and gamma. DNMT1 interacts with HP1 resulting in increased DNA methylation on DNA and chromatin templates in vitro. The functional and physical interaction can be recapitulated in vivo. Binding of GAL4-HP1 to a reporter construct is sufficient to induce repression and DNA methylation in DNMT1 wild-type but not DNMT1-null cells. Additionally, silencing of the Survivin gene coincides with recruitment of G9a and HP1 in DNMT1 wild-type but not null cells. We conclude that direct interactions between HP1 and DNMT1 mediate silencing of euchromatic genes.

Direct interaction between DNMT1 and G9a coordinates DNA and histone methylation during replication

Chromatin methylation is necessary for stable repression of gene expression during mammalian development. During cell division, DNMT1 maintains the DNA methylation pattern of the newly synthesized daughter strand, while G9a methylates H3K9. Here, DNMT1 is shown to directly bind G9a both in vivo and in vitro and to colocalize in the nucleus during DNA replication. The complex of DNMT1 and G9a colocalizes with dimethylated H3K9 (H3K9me2) at replication foci. Similarly, another H3K9 histone methyltransferase, SUV39H1, colocalizes with DNMT1 on heterochromatic regions of the nucleoli exclusively before cell division. Both DNMT1 and G9a are loaded onto the chromatin simultaneously in a ternary complex with loading factor PCNA during chromatin replication. Small interfering RNA (siRNA) knockdown of DNMT1 impairs DNA methylation, G9a loading, and H3K9 methylation on chromatin and rDNA repeats, confirming DNMT1 as the primary loading factor. Additionally, the complex of DNMT1 and G9a led to enhanced DNA and histone methylation of in vitro assembled chromatin substrates. Thus, direct cooperation between DNMT1 and G9a provides a mechanism of coordinated DNA and H3K9 methylation during cell division.

TFIID and human mediator coactivator complexes assemble cooperatively on promoter DNA

Activator-mediated transcription complex assembly on templates lacking chromatin requires the interaction of activators with two major coactivator complexes: TFIID and mediator. Here we employed immobilized template assays to correlate transcriptional activation with mediator and TFIID recruitment. In reactions reconstituted with purified proteins, we found that activator, TFIID, and mediator engage in reciprocal cooperative interactions to form a complex on promoter DNA. Preassembly of the coactivator complex accelerates the rate of transcription in a cell-free system depleted of TFIID and mediator. Our data argue that this coactivator complex is an intermediate in the assembly of an active transcription complex. Furthermore, the reciprocity of the interactions demonstrates that the complex could in principle be nucleated with either TFIID or mediator, implying that alternative pathways could be utilized to generate diversity in the way activators function in vivo.

Molecular engineering of a two-step transcription amplification (TSTA) system for transgene delivery in prostate cancer

Gene therapy is founded on the concept that tissue-specific promoters can express heterologous genes for molecular imaging or therapeutic applications. The engineering of cell-specific enhancers to improve potency and the development of two-step transcriptional activation (TSTA) approaches have significantly improved the efficacy of transgene expression. Here we combine these technologies to create a robust, titratable, androgen-responsive system targeted to prostate cancer cells. Our "chimeric" TSTA system uses a duplicated variant of the prostate-specific antigen (PSA) gene enhancer to express GAL4 derivatives fused to one, two, or four VP16 activation domains. We targeted the resulting activators to cells with reporter templates bearing one, two, or five GAL4 binding sites upstream of firefly luciferase. We monitored activity via firefly luciferase assays in transfected cell extracts and in live nude mice using a cooled charge-coupled device (CCD) imaging system. In this system, we found that firefly luciferase expression in prostate cancer cells can be varied over an 800-fold range. We also found that a single plasmid bearing the optimized enhancer, GAL4-VP16 derivative, and reporter expressed firefly luciferase at 20-fold higher levels than the cytomegalovirus enhancer. We discuss the implications of this strategy and its application to molecular imaging and therapy.

Placental morphogenesis in pregnancies with Down's syndrome might provide a clue to pre-eclampsia

Insufficient perfusion of placenta in pre-eclampsia is commonly associated with oxidative stress leading to increased superoxide formation and reduced invasion of uterine spiral arteries by differentiated migratory cytotrophoblasts. The superoxide dismutase (SOD) level, responsible for eliminating toxic superoxides, drops significantly in pre-eclampsia. On the contrary, the SOD synthesis increases dramatically, compared to that of normal placenta, in pregnancies with trisomy 21 (T21) fetus. However, despite a low level of placental hypoplasia, the overall perfusion of T21 placentae is comparable to that of normal pregnancy. In the light of recent reports on alternative modes of SOD function and factors regulating pathways of cytotrophoblast differentiation, here we have attempted to reconcile the two seemingly disparate pregnancy conditions and suggest that trisomy 21 pregnancies might provide new insight into our understanding of placental morphogenesis in pre-eclampsia.

Two-step transcriptional amplification as a method for imaging reporter gene expression using weak promoters

We are developing assays to image tissue-specific reporter gene expression in living mice by using optical methods and positron emission tomography. Approaches for imaging reporter gene expression depend on robust levels of mRNA and reporter protein. Attempts to image reporter gene expression driven by weak promoters are often hampered by the poor transcriptional activity of such promoters. Most tissue-specific promoters are weak relative to stronger but constitutively expressing viral promoters. In this study, we have validated methods to enhance the transcriptional activity of the prostate-specific antigen promoter for imaging by using a two-step transcriptional amplification (TSTA) system. We used the TSTA system to amplify expression of firefly luciferase (fl) and mutant herpes simplex virus type 1 thymidine kinase (HSV1-sr39tk) in a prostate cancer cell line (LNCaP). We demonstrate approximately 50-fold (fl) and approximately 12-fold (HSV1-sr39tk) enhancement by using the two-step approach. The TSTA system is observed to retain tissue selectivity. A cooled charge-coupled device optical imaging system was used to visualize the amplified fl expression in living mice implanted with LNCaP cells transfected ex vivo. These imaging experiments reveal a approximately 5-fold gain in imaging signal by using the TSTA system over the one-step system. The TSTA approach will be a valuable and generalizable tool to amplify and noninvasively image reporter gene expression in living animals by using tissue-specific promoters. The approaches validated should have important implications for study of gene therapy vectors, cell trafficking, transgenic models, as well as studying development of eukaryotic organisms.

Chimeric PSA enhancers exhibit augmented activity in prostate cancer gene therapy vectors

The native PSA enhancer and promoter confer prostate-specific expression when inserted into adenovirus vectors capable of efficient in vivo gene delivery, although the transcriptional activity is low. By exploiting properties of the natural PSA control regions, we have improved the activity and specificity of the prostate-specific PSA enhancer for gene therapy and imaging applications. Previous studies have established that androgen receptor (AR) molecules bind cooperatively to AREs in the PSA enhancer core (-4326 to -3935) and act synergistically with AR bound to the proximal promoter to regulate transcriptional output. To exploit the synergistic nature of AR action we generated chimeric enhancer constructs by (1) insertion of four tandem copies of the proximal AREI element; (2) duplication of enhancer core; or (3) removal of intervening sequences (-3744 to -2855) between the enhancer and promoter. By comparing to the baseline construct, PSE, containing the PSA enhancer (-5322 to -2855) fused to the proximal promoter (-541 to +12), the three most efficacious chimeric constructs, PSE-BA (insertion of ARE4), PSE-BC (duplication of core) and PSE-BAC (insertion of core and ARE4), are 7.3-, 18.9-, and 9.4-fold higher, respectively. These chimeric PSA enhancer constructs are highly androgen inducible and retain a high degree of tissue discriminatory capability. Initial biochemical studies reveal that the augmented activity of the chimeric constructs in vivo correlates with their ability to recruit AR and critical co-activators in vitro. The enhanced activity, inducibility and specificity of the chimeric constructs are retained in an adenoviral vector (Ad-PSE-BC-luc). Systemic administration of Ad-PSE-BC-luc into SCID mice harboring the LAPC-9 human prostate cancer xenografts shows that this prostate specific vector retained tissue discriminatory capability compared with a comparable cytomegalovirus (CMV) promoter driven vector.

Igf2/H19 imprinting control region (ICR): an insulator or a position-dependent silencer?

The imprinting control region (ICR) located far upstream of the H19 gene, in conjunction with enhancers, modulates the transcription of Igf2 and H19 genes in an allele-specific manner. On paternal inheritance, the methylated ICR silences the H19 gene and indirectly facilitates transcription from the distant Igf2 promoter, whereas on the maternal chromosome the unmethylated ICR, together with enhancers, activates transcription of the H19 gene and thereby contributes to the repression of Igf2. This repression of maternal Igf2 has recently been postulated to be due to a chromatin boundary or insulator function of the unmethylated ICR. Central to the insulator model is the site-specific binding of a ubiquitous nuclear factor CTCF which exhibits remarkable flexibility in functioning as transcriptional activator or silencer. We suggest that the ICR positioned close to the enhancers in an episomal context might function as a transcriptional silencer by virtue of interaction of CTCF with its modifiers such as SIN3A and histone deacetylases. Furthermore, a localised folded chromatin structure resulting from juxtaposition of two disparate regulatory sequences (enhancer ICR) could be the mechanistic basis of ICR-mediated position-dependent (ICR-promoter) transcriptional repression in transgenic Drosophila.

Quinazolines as cyclin dependent kinase inhibitors

Quinazolines have been identified as inhibitors of CDK4/D1 and CDK2/E. Aspects of the SAR were investigated using solution-phase, parallel synthesis. An X-ray crystal structure was obtained of quinazoline 51 bound in CDK2 and key interactions within the ATP binding pocket are defined.

Epigenotype-phenotype correlations in Beckwith-Wiedemann syndrome

Beckwith-Wiedemann syndrome (BWS) is a model imprinting disorder resulting from mutations or epigenetic events involving imprinted genes at chromosome 11p15.5. Thus, germline mutations in CDKN1C, uniparental disomy (UPD), and loss of imprinting of IGF2 and other imprinted genes have been implicated. Many familial BWS cases have germline CDKN1C mutations. However, most BWS cases are sporadic and UPD or putative imprinting errors predominate in this group. We have identified previously a subgroup of sporadic cases with loss of imprinting (LOI) of IGF2 and epigenetic silencing of H19 proposed to be caused by a defect in a distal 11p15.5 imprinting control element (designated BWSIC1). However, many sporadic BWS patients show biallelic IGF2 expression in the presence of normal H19 methylation and expression patterns. This and other evidence suggested the existence of a further imprinting control element (BWSIC2) at 11p15. 5. Recently, we showed that a subgroup of BWS patients have loss of methylation (LOM) at a differentially methylated region (KvDMR1) within the KCNQ1 gene centromeric to the IGF2 and H19 genes. We have now analysed a large series of sporadic cases to define the frequency and phenotypic correlates of epigenetic abnormalities in BWS. LOM at KvDMR1 was detected by Southern analysis or a novel PCR based method in 35 of 69 (51%) sporadic BWS without UPD. LOM at KvDMR1 was often, but not invariably associated with LOI of IGF2. KvDMR1 LOM was not detected in BWS patients with putative BWSIC1 defects and cases with KvDMR1 LOM (that is, putative BWSIC2 defects) invariably had a normal H19 methylation pattern. The incidence of exomphalos in putative BWSIC2 defect patients was not significantly different from that in patients with germline CDKN1C mutations (20/29 and 13/15 respectively), but was significantly greater than that in patients with putative BWSIC1 defects (0/5, p=0.007) and UPD (0/22, p<0.0001). These findings are consistent with the hypothesis that LOM of KvDMR1 (BWSIC2 defect) results in epigenetic silencing of CDKN1C and variable LOI of IGF2. BWS patients with embryonal tumours have UPD or a BWSIC1 defect but not LOM of KvDMR1. This study has further shown how (1) variations in phenotypic expression of BWS may be linked to specific molecular subgroups and (2) molecular analysis of BWS can provide insights into mechanisms of imprinting regulation.

Nurse-initiated thrombolysis in coronary care

National service frameworks emphasise the importance of people who are experiencing a myocardial infarction receiving thrombolysis as quickly as possible. Nurse-initiated thrombolysis is one way to safely achieve the standards.

Medical consultants' attitudes towards nurse assessment and initiation of thrombolysis prior to medical screening

This study explores medical consultants' attitudes to the concept and introduction of nurse-initiated thrombolysis within a coronary care unit. A self-administered questionnaire was used to gauge attitudes of consultants who care for patients admitted to coronary care. Themes that emerged were: conceptual awareness, medico-legal aspects and professional preparedness. Further research is advocated to explore the attitudes and experiences of nurses and physicians involved in the practice of nurse-initiated thrombolysis.

What are the attitudes of coronary care nurses towards the introduction of nurse-initiated thrombolysis?

This study explores nurses' attitudes to the introduction of nurse-initiated thrombolysis, within a large district coronary care unit. A qualitative survey was used to elicit attitudes from all ENB 124 qualified members of staff presently employed within the unit. Concerns expressed by the nursing staff, prior to introduction of this practice, are described. Four key themes emerging from the data are explored; framework for practice; scope for advanced practice; decision-making policy; personal attributes. With the increased introduction of nurse-initiated thrombolysis, further research within this area is advocated.

Crystallization and preliminary X-ray diffraction data of the complex of recombinant tick anticoagulant peptide (rTAP) and bovine factor Xa

The complex of bovine factor Xa and recombinant tick anticoagulant peptide (rTAP) was crystallized in two different crystal forms using polyethylene glycol as a precipitant. Form I belongs to space group P42212 with unit-cell dimensions a = b = 133.1, c = 68.8 A. It contains one complex per asymmetric unit and diffracts to 3.0 A resolution. Form II belongs to P41212 (or P43212) with dimensions a = b = 126.5, c = 146.7 A; it contains two complexes per asymmetric unit and diffracts to 2.5 A. The crystals of both forms consist of factor Xa (MW = 45.3 kDa) and rTAP (MW = 6.7 kDa).

Chromatin modification of imprinted H19 gene in mammalian spermatozoa

The allele-specific epigenetic markings of endogenously imprinted genes in placental mammals occur during gametogenesis. The identification of the molecular nature of gametic imprints is the first step towards understanding the mechanistic basis of epigenesis in embryonic and adult somatic tissues. The specific question addressed in this work is whether the closely positioned but oppositely imprinted insulin-like growth factor 2 (IGF 2) and H19 genes, which have similar temporal regulation during development, differ in chromatin structure in mammalian spermatozoa. During terminal differentiation of mammalian spermatozoa, about 3-15% of the haploid genome retains a quasisomatic-type chromatin structure, whereas the remaining genomes interact with protamines that are further cross-linked by-S-S- bridges. Micrococcal nuclease (MNase) and DNase I digestions of human (HSN) and porcine sperm nuclei (PSN) showed that the IGF 2 gene in both types of nuclei retained somatic-type nucleosomes that were close-packed with a periodicity of 150 bp. However, the H19 gene in both species was predominantly organised by unique structural repeats, which were 650-674 bp in PSN and 438-522 bp in HSN, condensing at least 20 kb of chromatin. These results, together with previous studies, suggest that epigenetic chromatin modification leading to preferential condensation of the paternal H19 allele in embryonic tissues is already present in the germ cells.

New inhibitors of thrombin and other trypsin-like proteases: hydrogen bonding of an aromatic cyano group with a backbone amide of the P1 binding site replaces binding of a basic side chain

Highly effective thrombin inhibitors have been obtained by preparing boronic acid analogues of m-cyano-substituted phenylalanine and its incorporation into peptides. The cyano group enhances binding by several orders of magnitude. For example, Ac-(D)Phe-Pro-boroPheOH binds to thrombin with a Ki of 320 nM and the Ki of Ac-(D)Phe-Pro-boroPhe(m-CN)-OH is 0.79 nM. Protein crystal structure determination of trypsin complexed to H-(D)Phe-Pro-boroPhe(m-CN)-OH indicates that the aromatic side chain is bound in the P1 binding site and that the cyano group can act as a H-bond acceptor for the amide proton of Gly219. Enhanced binding for inhibitors containing the m-cyano group was observed for coagulation factor Xa and for the factor VIIa.tissue factor complex [Ki values of Ac-(D)Phe-Pro-boroPhe(mCN)-OH are 760 and 3.3 nM, respectively]. This result is consistent with the sequence homology of these two enzymes in the P1 binding site. Two enzymes lacking the strict homology in the P1 binding site, pancreatic kallikrein and chymotrypsin, did not exhibit significantly enhanced binding.

Variant cDNA sequences of human ATP:citrate lyase: cloning, expression, and purification from baculovirus-infected insect cells

ATP:citrate lyase (ACL) is a major generator of cytosolic acetyl-coenzymeA, which is required for both fatty acid and cholesterol biosynthesis. The human ACL (hACL) cDNA was cloned by RT-PCR, and our results indicate the existence of previously unknown sequence variations in hACL. Expression of the hACL cDNA in Spodoptera frugiperda 9 insect cells resulted in the production of high levels of soluble, active enzyme. The recombinant protein (re-hACL) was purified to homogeneity from the soluble lysate of infected cells and was observed to exist as a tetramer by gel filtration chromatography. Kinetic analyses indicated that the re-hACL and rat ACL have very similar enzymological properties. The facile preparation of milligram quantities of purified, active re-hACL affords the opportunity to characterize the enzyme for structure-based design of hypolipidemic drugs, and to further examine the functional significance of the sequence variations.

ATP-dependent reorganization of human sperm nuclear chromatin

Chromosomes in terminally differentiated mammalian spermatozoa are extensively condensed by protamines but a small proportion of histones remain. We examined the primary organization of somatic-type chromatin in lysolecithin-permeabilized human sperm nuclei and report that nucleosomes are closely packed with a periodicity of approximately 150 bp. Incubation of nuclei in the presence of exogenous Mg2+ and ATP induced chromatin reorganization leading to an increase in spacing of the nucleosomes to approximately 190 bp. This ATP-dependent chromatin rearrangement involved phosphorylation of both protamine and histone H2a. Increase in linker length between nucleosomes correlated with the phosphorylation of H2aX, the major H2a variant in human spermatozoa, predominantly at the C-terminal end. Chromatin reorganization was independent of detectable nuclear dispersion, which is an early chromosomal event in male pronuclear formation during fertilization.

Galactose-1-phosphate uridylyltransferase. Purification of the enzyme and stereochemical course of each step of the double-displacement mechanism

A convenient new procedure for purifying galactose-1-phosphate uridylyltransferase from Escherichia coli is described. It departs from earlier methods by introducing the use of a Cibacron Blue-agarose (Bio-Rad Affi-Gel Blue) at an early stage. Purification is completed by ion-exchange chromatography using DEAE-Sephadex A-50. The procedure is substantially shorter than earlier methods and reproducibly yields enzyme of high specific activity suitable for use in structural work such as characterization of the intermediate uridylyl-enzyme. The first step of the galactose-1-P uridylyltransferase reaction is the transfer of the uridylyl group from UDP-glucose to N3 of a histidine residue in the enzyme to form the covalent uridylyl-enzyme and glucose-1-P. The uridylyl-enzyme intermediate then reacts in a second step with galactose-1-P to form UDP-galactose. The enzyme accepts (RP)-UDP alpha S-glucose as a good substrate, converting it to (RP)-UDP alpha S-galactose, i.e., with overall retention of configuration. In this paper we show that reaction of the enzyme with (RP)-[2-14C]UDP alpha S-glucose produces a [2-14C]uridylyl alpha S-enzyme that can be converted by base-catalyzed cyclization to (RP)-[2-14C]cUMPS. Inasmuch as cyclization must have proceeded with inversion of configuration at phosphorus, the corresponding configuration in the intermediate must have been the inverse of that in the substrate. Therefore, formation of uridylyl alpha S-enzyme from (RP)-UDP alpha S-glucose proceeds with inversion of configuration, and overall retention arises from inversion in each of the two steps. The results support the authenticity of the isolated uridylyl-enzyme as the true reaction intermediate.(ABSTRACT TRUNCATED AT 250 WORDS)