peaksat: an R package for ChIP-seq peak saturation analysis.

BACKGROUND: Epigenomic profiling assays such as ChIP-seq have been widely used to map the genome-wide enrichment profiles of chromatin-associated proteins and posttranslational histone modifications. Sequencing depth is a key parameter in experimental design and quality control. However, due to variable sequencing depth requirements across experimental conditions, it can be challenging to determine optimal sequencing depth, particularly for projects involving multiple targets or cell types. RESULTS: We developed the peaksat R package to provide target read depth estimates for epigenomic experiments based on the analysis of peak saturation curves. We applied peaksat to establish the distinctive read depth requirements for ChIP-seq studies of histone modifications in different cell lines. Using peaksat, we were able to estimate the target read depth required per library to obtain high-quality peak calls for downstream analysis. In addition, peaksat was applied to other sequence-enrichment methods including CUT&RUN and ATAC-seq. CONCLUSION: peaksat addresses a need for researchers to make informed decisions about whether their sequencing data has been generated to an adequate depth and subsequently sufficient meaningful peaks, and failing that, how many more reads would be required per library. peaksat is applicable to other sequence-based methods that include calling peaks in their analysis.

Surgeon and Patient Reports of Fertility Preservation Referral and Uptake in a Prospective, Pan-Canadian Study of Young Women with Breast Cancer.

BACKGROUND: Prompt referral by their surgeon enables fertility preservation (FP) by young women with breast cancer (YWBC) without treatment delay. Following a FP knowledge intervention, we evaluated surgeon and patient reports of fertility discussion, FP referral offer and uptake, and FP choices and reasons for declining FP among patients enrolled in the Reducing Breast Cancer in Young Women, prospective pan-Canadian study. METHODS: Between September 2015 and December 2020, 1271 patients were enrolled at 31 sites. For each patient, surgeons were sent a questionnaire inquiring whether: (1) fertility discussion was initiated by the surgical team; (2) FP referral was offered; (3) referral was accepted; a reason was requested for any "no" response. Patients were surveyed about prediagnosis fertility plans and postdiagnosis oncofertility management. RESULTS: Surgeon questionnaires were completed for 1068 (84%) cases. Fertility was discussed with 828 (84%) and FP consultation offered to 461 (47%) of the 990 YWBC with invasive disease. Among the 906 responding YWBC, referral was offered to 220 (82%) of the 283 (33%) with invasive disease who stated that they had definitely/probably not completed childbearing prediagnosis. Of these, 133 (47%) underwent FP. The two most common reasons for not choosing FP were cost and unwillingness to delay treatment. CONCLUSIONS: Although the rates of surgeon fertility discussion and FP referral was higher than most reports, likely due to our previous intervention, further improvement is desirable. FP should be offered to all YWBC at diagnosis, regardless of perceived childbearing intent. Cost remains an important barrier to FP uptake.

Exchange of associated factors directs a switch in HBO1 acetyltransferase histone tail specificity.

Histone acetyltransferases (HATs) assemble into multisubunit complexes in order to target distinct lysine residues on nucleosomal histones. Here, we characterize native HAT complexes assembled by the BRPF family of scaffold proteins. Their plant homeodomain (PHD)-Zn knuckle-PHD domain is essential for binding chromatin and is restricted to unmethylated H3K4, a specificity that is reversed by the associated ING subunit. Native BRPF1 complexes can contain either MOZ/MORF or HBO1 as catalytic acetyltransferase subunit. Interestingly, while the previously reported HBO1 complexes containing JADE scaffold proteins target histone H4, the HBO1-BRPF1 complex acetylates only H3 in chromatin. We mapped a small region to the N terminus of scaffold proteins responsible for histone tail selection on chromatin. Thus, alternate choice of subunits associated with HBO1 can switch its specificity between H4 and H3 tails. These results uncover a crucial new role for associated proteins within HAT complexes, previously thought to be intrinsic to the catalytic subunit.

Insights into the Genetic Variations of Human Cytochrome P450 2C9: Structural Analysis, Characterization and Comparison.

Cytochromes P450 (CYP) are one of the major xenobiotic metabolizing enzymes with increasing importance in pharmacogenetics. The CYP2C9 enzyme is responsible for the metabolism of a wide range of clinical drugs. More than sixty genetic variations have been identified in CYP2C9 with many demonstrating reduced activity compared to the wild-type (WT) enzyme. The CYP2C9*8 allele is predominantly found in persons of African ancestry and results in altered clearance of several drug substrates of CYP2C9. The X-ray crystal structure of CYP2C9*8, which represents an amino acid variation from arginine to histidine at position 150 (R150H), was solved in complex with losartan. The overall conformation of the CYP2C9*8-losartan complex was similar to the previously solved complex with wild type (WT) protein, but it differs in the occupancy of losartan. One molecule of losartan was bound in the active site and another on the surface in an identical orientation to that observed in the WT complex. However, unlike the WT structure, the losartan in the access channel was not observed in the *8 complex. Furthermore, isothermal titration calorimetry studies illustrated weaker binding of losartan to *8 compared to WT. Interestingly, the CYP2C9*8 interaction with losartan was not as weak as the CYP2C9*3 variant, which showed up to three-fold weaker average dissociation constant compared to the WT. Taken together, the structural and solution characterization yields insights into the similarities and differences of losartan binding to CYP2C9 variants and provides a useful framework for probing the role of amino acid substitution and substrate dependent activity.

Coordination of Di-Acetylated Histone Ligands by the ATAD2 Bromodomain.

The ATPase Family, AAA domain-containing protein 2 (ATAD2) bromodomain (BRD) has a canonical bromodomain structure consisting of four α-helices. ATAD2 functions as a co-activator of the androgen and estrogen receptors as well as the MYC and E2F transcription factors. ATAD2 also functions during DNA replication, recognizing newly synthesized histones. In addition, ATAD2 is shown to be up-regulated in multiple forms of cancer including breast, lung, gastric, endometrial, renal, and prostate. Furthermore, up-regulation of ATAD2 is strongly correlated with poor prognosis in many types of cancer, making the ATAD2 bromodomain an innovative target for cancer therapeutics. In this study, we describe the recognition of histone acetyllysine modifications by the ATAD2 bromodomain. Residue-specific information on the complex formed between the histone tail and the ATAD2 bromodomain, obtained through nuclear magnetic resonance spectroscopy (NMR) and X-ray crystallography, illustrates key residues lining the binding pocket, which are involved in coordination of di-acetylated histone tails. Analytical ultracentrifugation, NMR relaxation data, and isothermal titration calorimetry further confirm the monomeric state of the functionally active ATAD2 bromodomain in complex with di-acetylated histone ligands. Overall, we describe histone tail recognition by ATAD2 BRD and illustrate that one acetyllysine group is primarily engaged by the conserved asparagine (N1064), the "RVF" shelf residues, and the flexible ZA loop. Coordination of a second acetyllysine group also occurs within the same binding pocket but is essentially governed by unique hydrophobic and electrostatic interactions making the di-acetyllysine histone coordination more specific than previously presumed.

Structure of Cytochrome P450 2C9*2 in Complex with Losartan: Insights into the Effect of Genetic Polymorphism.

The human CYP2C9 plays a crucial role in the metabolic clearance of a wide range of clinical therapeutics. The *2 allele is a prevalent genetic variation in CYP2C9 that is found in various populations. A marked reduction of catalytic activity toward many important drug substrates has been demonstrated by CYP2C9*2, which represents an amino acid variation at position 144 from arginine to cysteine. The crystal structure of CYP2C9*2 in complex with an antihypertensive drug losartan was solved using X-ray crystallography at 3.1-Å resolution. The Arg144Cys variation in the *2 complex disrupts the hydrogen-bonding interactions that were observed between the side chain of arginine and neighboring residues in the losartan complex of CYP2C9 and the wild-type (WT) ligand-free structure. The conformation of several secondary structural elements is affected, thereby altering the binding and orientation of drug and important amino acid side chains in the distal active site cavity. The new structure revealed distinct interactions of losartan in the compact active site of CYP2C9*2 and differed in occupancy at the other binding sites previously identified in the WT-losartan complex. Furthermore, the binding studies in solution using losartan illustrated lower activity of the CYP2C9*2 compared with the WT. Together, the findings yield valuable insights into the decreased hydroxylation activity of losartan in patients carrying CYP2C9*2 allele and provide a useful framework to investigate the effect of a single-nucleotide polymorphism that leads to altered metabolism of diverse drug substrates. SIGNIFICANCE STATEMENT: The *2 allele of the human drug-metabolizing enzyme CYP2C9 is found in different populations and results in significantly reduced activity toward various drug substrates. How the CYP2C9*2 variant induces altered drug metabolism is poorly understood given that the Arg144Cys variation is located far away from the active site. This work yield insight into the effect of distal variation using multitude of techniques that include X-ray crystallography, isothermal titration calorimetry, enzymatic characterization, and computational studies.

Effect of a Knowledge-Translation Intervention on Breast Surgeons' Oncofertility Attitudes and Practices.

BACKGROUND: The breast surgeon, generally the first oncology specialist consulted, is ideally suited to offer fertility preservation (FP) referral to young women with breast cancer (YWBC). In the authors' 2015 survey of 84 surgeons participating in the pan-Canadian RUBY study of YWBC, oncofertility knowledge and rates of FP referral were suboptimal. The authors designed an oncofertility knowledge-translation intervention for surgeons. METHODS: A customized oncofertility toolbox was created including a seminar/webinar, an option grid, a three-question FP survey sent upon registration of each RUBY patient, and a management checklist. In 2018, the 28 site lead surgeons were re-invited to participate in a follow-up telephone interview, and 85 non-site lead surgeons were invited to complete a follow-up online questionnaire. RESULTS: A total of 27 site lead surgeons consented to be re-interviewed. After the intervention, 85% indicated that they "routinely" initiated a fertility discussion compared with 54% at baseline (p < 0.005), with 56% stating that the toolbox had been helpful for making positive changes in their practice regarding oncofertility, and 44% stating that they found it easier to initiate a fertility discussion. Among the 55 non-site lead surgeons who completed the questionnaire, a significant improvement in oncofertility knowledge was found. The percentage reporting "rarely" or "never" discussing FP options decreased from 41 to 14% (p < 0.005), and 84% stated that they referred patients who had not completed their families and were at risk for infertility to FP consultation compared with 32% before the intervention (p < 0.001). CONCLUSIONS: A multi-pronged but simple knowledge-translation intervention improved the attitudes, knowledge, and FP practice of Canadian breast surgeons.

Safety and Assisted Reproductive Technology Outcomes of Hysteroscopic Tubal Microinserts Versus Laparoscopic Proximal Tubal Occlusion or Salpingectomy for Hydrosalpinges Treatment.

OBJECTIVE: This study sought to answer the following question: What are the complications and assisted reproductive technology outcomes among women with hydrosalpinges managed by hysteroscopic microinsert tubal occlusion compared with women with hydrosalpinges managed by laparoscopic proximal tubal occlusion or salpingectomy? METHODS: This was a retrospective cohort study conducted from January 2009 to December 2014 at two academic, tertiary care, in vitro fertilization centres in Toronto, Ontario. All patients (n = 52) who underwent hysteroscopic tubal occlusion for hydrosalpinges were identified. Patients who proceeded with embryo transfer cycles after hysteroscopic microinsert (n = 33) were further age matched to a cohort of patients who underwent embryo transfer after laparoscopic proximal tubal occlusion or salpingectomy (n = 33). Main outcome measures were clinical pregnancy rate per patient and per embryo transfer cycle. RESULTS: Among 33 patients, there were 39 fresh and 37 frozen embryo transfer cycles in the hysteroscopic group (group A); among 33 patients in the laparoscopic group (group B), there were 42 fresh and 29 frozen embryo transfer cycles. The cumulative clinical pregnancy rate in group A and group B was similar (66.7% vs. 69.7%, respectively; P = 0.8). The clinical pregnancy rate per embryo transfer cycle was also similar in both groups (28.9% in group A vs. 32.4% in group B; P = 0.6). There were two incidents of ectopic pregnancy in the laparoscopic group and no ectopic pregnancy in the hysteroscopic group. There were three major complications: tubo-ovarian abscess, distal migration of the coil after microinsert placement, and an acute abdomen following the hysteroscopic procedure. CONCLUSION: Pregnancy outcomes after hysteroscopic placement of a microinsert for hydrosalpinx management before embryo transfer were comparable to those following laparoscopic proximal tubal occlusion or salpingectomy. However, caution is advised regarding microinsert placement for hydrosalpinges before proceeding with assisted reproductive technology.

Disulfide bridge formation influences ligand recognition by the ATAD2 bromodomain.

The ATPase family, AAA domain-containing protein 2 (ATAD2) has a C-terminal bromodomain, which functions as a chromatin reader domain recognizing acetylated lysine on the histone tails within the nucleosome. ATAD2 is overexpressed in many cancers and its expression is correlated with poor patient outcomes, making it an attractive therapeutic target and potential biomarker. We solved the crystal structure of the ATAD2 bromodomain and found that it contains a disulfide bridge near the base of the acetyllysine binding pocket (Cys1057-Cys1079). Site-directed mutagenesis revealed that removal of a free C-terminal cysteine (C1101) residue greatly improved the solubility of the ATAD2 bromodomain in vitro. Isothermal titration calorimetry experiments in combination with the Ellman's assay demonstrated that formation of an intramolecular disulfide bridge negatively impacts the ligand binding affinities and alters the thermodynamic parameters of the ATAD2 bromodomain interaction with a histone H4K5ac peptide as well as a small molecule bromodomain ligand. Molecular dynamics simulations indicate that the formation of the disulfide bridge in the ATAD2 bromodomain does not alter the structure of the folded state or flexibility of the acetyllysine binding pocket. However, consideration of this unique structural feature should be taken into account when examining ligand-binding affinity, or in the design of new bromodomain inhibitor compounds that interact with this acetyllysine reader module.

Reproductive and Hormonal Considerations in Women at Increased Risk for Hereditary Gynecologic Cancers: Society of Gynecologic Oncology and American Society for Reproductive Medicine Evidence-Based Review.

Providers who care for women at risk for hereditary gynecologic cancers must consider the impact of these conditions on reproductive and hormonal health. This document reviews potential options for cancer prevention, family building, genetic testing and management of surgical menopause in this patient population. Capsule: Women predisposed to hereditary gynecologic cancer have options for fertility preservation, preimplantation genetic testing to select embryos without pathogenic variants, pregnancy through gestational carriers after hysterectomy and hormone replacement.

Biological function and histone recognition of family IV bromodomain-containing proteins.

Bromodomain proteins function as epigenetic readers that recognize acetylated histone tails to facilitate the transcription of target genes. There are approximately 60 known human bromodomains, which are divided into eight sub-families based on structural conservation. The bromodomain-containing proteins in family IV include seven members (BRPF1, BRPF2, BRPF3, BRD7, BRD9, ATAD2, and ATAD2b). The bromodomains of each of these proteins recognize and bind acetyllysine residues on histone tails protruding from the nucleosome. However, the histone marks recognized by each bromodomain protein can be very different. The BRPF1 subunit of the MOZ histone acetyltransferase (HAT) recognizes acetylated histones H2AK5ac, H4K12ac, H3K14ac, H4K8ac, and H4K5ac. While the bromodomain of BRD7, a member of the SWI/SNF complex, was shown to preferentially recognize acetylated histones H3K9ac, H3K14ac, H4K8ac, H4K12ac, and H4K16ac. The bromodomains of BRPF2 and BRPF3 have similar sequences, and function as part of the HBO1 HAT complex, but there is limited data on which histone ligands they bind. Similarly, there is little known about the histone targets of the BRD9 and ATAD2b bromodomain proteins. Interestingly, the ATAD2 bromodomain was recently shown to preferentially bind to the di-acetylated H4K5acK12ac mark found in newly synthesized histones following DNA replication. However, despite the physiological importance of the family IV bromodomains, little is known about how they function at the molecular or atomic level. In this review, we summarize our understanding of how family IV bromodomains recognize and select for acetyllysine marks and discuss the importance of acetylated histone recognition for their biological functions.

Mechanism of Histone H3K4me3 Recognition by the Plant Homeodomain of Inhibitor of Growth 3.

Aberrant access to genetic information disrupts cellular homeostasis and can lead to cancer development. One molecular mechanism that regulates access to genetic information includes recognition of histone modifications, which is carried out by protein modules that interact with chromatin and serve as landing pads for enzymatic activities that regulate gene expression. The ING3 tumor suppressor protein contains a plant homeodomain (PHD) that reads the epigenetic code via recognition of histone H3 tri-methylated at lysine 4 (H3K4me3), and this domain is lost or mutated in various human cancers. However, the molecular mechanisms targeting ING3 to histones and the role of this interaction in the cell remain elusive. Thus, we employed biochemical and structural biology approaches to investigate the interaction of the ING3 PHD finger (ING3PHD) with the active transcription mark H3K4me3. Our results demonstrate that association of the ING3PHD with H3K4me3 is in the sub-micromolar range (KD ranging between 0.63 and 0.93 µm) and is about 200-fold stronger than with the unmodified histone H3. NMR and computational studies revealed an aromatic cage composed of Tyr-362, Ser-369, and Trp-385 that accommodate the tri-methylated side chain of H3K4. Mutational analysis confirmed the critical importance of Tyr-362 and Trp-385 in mediating the ING3PHD-H3K4me3 interaction. Finally, the biological relevance of ING3PHD-H3K4me3 binding was demonstrated by the failure of ING3PHD mutant proteins to enhance ING3-mediated DNA damage-dependent cell death. Together, our results reveal the molecular mechanism of H3K4me3 selection by the ING3PHD and suggest that this interaction is important for mediating ING3 tumor suppressive activities.

Oncofertility Knowledge, Attitudes, and Practices of Canadian Breast Surgeons.

BACKGROUND: Guidelines recommend that oncologists discuss treatment-related fertility issues with young cancer patients as early as possible after diagnosis and, if appropriate, expedite referral for fertility preservation (FP). This study sought to determine the attitudes and practices of Canadian breast surgeons regarding fertility issues, as well as barriers to and facilitators of fertility discussion and referrals. METHODS: Semistructured telephone interviews were conducted with 28 site lead surgeons (SLSs) at 28 (97 %) of 29 centers (25 % cancer centers, 64 % teaching hospitals) across Canada participating in RUBY, a pan-Canadian research program for young women with breast cancer. In addition, 56 (65 %) of 86 of their surgical colleagues (non-site lead surgeons [NSLSs]) completed an online survey of their oncofertility knowledge, attitudes, and practices. RESULTS: Of the 28 SLSs (43 % male, 36 % in practice <10 years), 46 % had inadequate oncofertility knowledge, 25 % discussed fertility only if mentioned by the patient, 21 % believed fertility discussion and referral were the mandate of the medical oncologist, and 45 % did not know of an FP center in their area. More than 80 % of the NSLSs (54 % male, 30 % in practice <10 years) were unfamiliar with oocyte or embryo cryopreservation; 36 % never or rarely discussed fertility issues; and 51 % thought referral to a fertility specialist was not their responsibility. CONCLUSIONS: Oncofertility knowledge was low among the SLSs, especially the NSLSs, and barriers to referral were identified. An oncofertility knowledge translation intervention specifically for breast surgeons is being developed to increase surgeon knowledge and awareness of oncofertility issues and referral.

Curcumin and dimethoxycurcumin induced epigenetic changes in leukemia cells.

PURPOSE: Curcumin is an ideal chemopreventive and antitumor agent characterized by poor bioavailability and low stability. The development of synthetic structural analogues like dimethoxycurcumin (DMC) could overcome these drawbacks. In this study we compared the cytotoxicity, metabolism and the epigenetic changes induced by both drugs in leukemia cells. METHODS: Apoptosis and cell cycle analysis were analyzed by flow cytometry. Real-time PCR was used for gene expression analysis. DNA methylation was analyzed by DNA pyrosequencing. The metabolic stability was determined using human pooled liver microsomes. Chromatin Immunoprecipitation was used to quantify histone methylation. RESULTS: Clinically relevant concentration of curcumin and DMC were not cytotoxic to leukemia cells and induced G2/M cell cycle arrest. DMC was more metabolically stable than curcumin. Curcumin and DMC were devoid of DNA hypomethylating activity. DMC induced the expression of promoter methylated genes without reversing DNA methylation and increased H3K36me3 mark near the promoter region of hypermethylated genes. CONCLUSION: DMC is a more stable analogue of curcumin that can induce epigenetic changes not induced by curcumin. DMC induced the expression of promoter methylated genes. The combination of DMC with DNA methyltransferase inhibitors could harness their combined induced epigenetic changes for optimal re-expression of epigenetically silenced genes.

The MOZ histone acetyltransferase in epigenetic signaling and disease.

The monocytic leukemic zinc finger (MOZ) histone acetyltransferase (HAT) plays a role in acute myeloid leukemia (AML). It functions as a quaternary complex with the bromodomain PHD finger protein 1 (BRPF1), the human Esa1-associated factor 6 homolog (hEAF6), and the inhibitor of growth 5 (ING5). Each of these subunits contain chromatin reader domains that recognize specific post-translational modifications (PTMs) on histone tails, and this recognition directs the MOZ HAT complex to specific chromatin substrates. The structure and function of these epigenetic reader modules has now been elucidated, and a model describing how the cooperative action of these domains regulates HAT activity in response to the epigenetic landscape is proposed. The emerging role of epigenetic reader domains in disease, and their therapeutic potential for many types of cancer is also highlighted.

Prenatal cell-free DNA screening for chromosomal aneuploidies after euploid embryo transfer shows high concordance with preimplantation genetic testing for aneuploidy results and low positive predictive values.

OBJECTIVE: To evaluate the positive predictive value (PPV) of prenatal cell-free DNA (cfDNA) screening for chromosomal aneuploidies in pregnancies achieved either after single euploid transfer in in vitro fertilization or Preimplantation Genetic Testing for Aneuploidy (PGT-A) cycles or transfer of single untested embryo, and to assess the concordance of prenatal-cfDNA-screening and PGT-A results. DESIGN: Single center retrospective cohort study. SETTING: Fertility clinic. PATIENT(S): A total of 2,973 prenatal-cfDNA-screening results for the most common trisomies (T13, T18, T21, X, and Y) and microdeletions (1p36, 4p16.3, 5p15.2, 15q11.2, and 22q11.2) from singleton pregnancies allocated into two groups: PGT-A group (n = 1,204) pregnant after single euploid transfer and non-PGT-A group (n = 1769) pregnant after transfer of single untested embryo, between 2016 and 2023. INTERVENTION(S): Not applicable. MAIN OUTCOME MEASURE(S): The primary outcome measure was the accuracy of prenatal-cfDNA screening. Positive and negative prenatal-cfDNA-screening results and subsequent prenatal or postnatal diagnostic testing were used to classify each positive prenatal-cfDNA-screening result as a true or a false positive. Secondary endpoints were to evaluate the concordance of PGT-A and prenatal-cfDNA-screening results and to assess the differences in the fetal fraction of cfDNA used for prenatal-cfDNA-screening reports between the study groups. RESULT(S): Prenatal-cfDNA screening was performed at a mean 11.3 ± 1.8 weeks gestational age, and yielded results in 99.9% of the patients (0.1% cancellation rate). There was no difference in the fetal fraction between PGT-A tested and not tested pregnancies (9.5% ± 4% vs. 10.3% ± 4%). 13 positive prenatal-cfDNA-screening results (two T21, two X0, four XXX, one XYY, one indeterminate sex, two 22q11 del/dup, and one 15q11.2del) were received for PGT-A group. Only one (22q11 dup) was confirmed with amniocentesis and fetal autopsy, giving a PPV for an abnormal prenatal-cfDNA screening of 7.7%, the rest had results concordant with PGT-A. Sex chromosomes were 100% concordant between prenatal-cfDNA-screening and PGT-A results, giving a 100% PPV for PGT-A for sex chromosomes and 100% negative predictive value for aneuploidies. Positive prenatal-cfDNA-screening results were received for 27 pregnancies from untested embryos (1.5%), follow-up testing was electively performed for 21, and 8 had confirmed the prenatal-cfDNA-screening result, giving a PPV for the non-PGT-A group of 38%. CONCLUSION(S): This study demonstrates that patients undergoing in vitro fertilization/PGT-A and single euploid embryo transfer can reliably do prenatal-cfDNA screening during their first trimester. Fetal fraction in singleton pregnancies after PGT-A tested embryos is not different from pregnancies with untested embryos. Positive predictive value for an abnormal prenatal-cfDNA-screening result after euploid embryo transfer was reassuringly low (7.7%). PGT-A reliably selects against aneuploidy with 100% concordance with fetal sex.

Structural and biophysical analysis of cytochrome P450 2C9*14 and *27 variants in complex with losartan.

The human cytochrome P450 (CYP) 1, 2 and 3 families of enzymes are responsible for the biotransformation of a majority of the currently available pharmaceutical drugs. The highly polymorphic CYP2C9 predominantly metabolizes many drugs including anticoagulant S-warfarin, anti-hypertensive losartan, anti-diabetic tolbutamide, analgesic ibuprofen, etc. There are >80 single nucleotide changes identified in CYP2C9, many of which significantly alter the clearance of important drugs. Here we report the structural and biophysical analysis of two polymorphic variants, CYP2C9*14 (Arg125His) and CYP2C9*27 (Arg150Leu) complexed with losartan. The X-ray crystal structures of the CYP2C9*14 and *27 illustrate the binding of two losartan molecules, one in the active site near heme and another on the periphery. Both losartan molecules are bound in an identical conformation to that observed in the previously solved CYP2C9 wild-type complex, however, the number of losartan differs from the wild-type structure, which showed binding of three molecules. Additionally, isothermal titration calorimetry experiments reveal a lower binding affinity of losartan with *14 and *27 variants when compared to the wild-type. Overall, the results provide new insights into the effects of these genetic polymorphisms and suggests a possible mechanism contributing to reduced metabolic activity in patients carrying these alleles.

Impact of Combinatorial Histone Modifications on Acetyllysine Recognition by the ATAD2 and ATAD2B Bromodomains.

The ATPase family AAA+ domain containing 2 (ATAD2) protein and its paralog ATAD2B have a C-terminal bromodomain (BRD) that functions as a reader of acetylated lysine residues on histone proteins. Using a structure-function approach, we investigated the ability of the ATAD2/B BRDs to select acetylated lysine among multiple histone post-translational modifications. The ATAD2B BRD can bind acetylated histone ligands that also contain adjacent methylation or phosphorylation marks, while the presence of these modifications significantly weakened the acetyllysine binding activity of the ATAD2 BRD. Our structural studies provide mechanistic insights into how ATAD2/B BRD-binding pocket residues coordinate the acetyllysine group in the context of adjacent post-translational modifications. Furthermore, we investigated how sequence changes in amino acids of the histone ligands impact the recognition of an adjacent acetyllysine residue. Our study highlights how the interplay between multiple combinations of histone modifications influences the reader activity of the ATAD2/B BRDs, resulting in distinct binding modes.