The Important Roles of Steroid Sulfatase and Sulfotransferases in Gynecological Diseases

Adenomyosis: genetics of estrogen metabolism

Background To analyze the allelic variants of genes of enzymes involved in estrogen metabolism: CYP1A1, CYP1A2, CYP19 and SULT1A1 using polymerase chain reaction-restriction fragment length polymorphism-restriction fragment length polymorphism (PCR-RFLP) analysis of women with histologically confirmed adenomyosis and women without proliferative diseases of pelvic organs was performed. We studied the following polymorphisms: CYP1A1 M1, T264 → C transition in the 3'-noncoding region; CYP1A2*1F, C734 → A transversion in CYP1A2 gene; C → T transition (Arg264Cys) in exon 7 of CYP19; SULT1A1*2, G638 → A transition (Arg213His) in the SULT1A1 gene. Materials and methods The study included 804 patients. Group I (experimental group) consisted of 268 women with adenomyosis. Inclusion criteria were: histological verification of adenomyosis, consent of patients to participate in the study. Group II (control group) - 536 women without proliferative diseases of the uterus. Inclusion criteria were: lack of proliferative processes of the uterus histologically confirmed by ultrasound examination, patient's consent to participate in the study. Results We found the significant association of C allele, T/C and C/C genotypes of the CYP1A1 gene (CYP1A1 M1 polymorphism), A allele, C/A and A/A genotypes of the CYP1A2 gene (CYP1A2*1F polymorphism) and the T allele, C/T and C/C genotypes of the CYP19 (Arg264Cys polymorphism) gene with the risk for adenomyosis. Conclusions Patients with adenomyosis had increased frequency of C allele, T/C and C/C genotypes of the CYP1A1 gene, A allele, C/A and A/A genotypes of the CYP1A2 gene and T allele and C/T and C/C genotypes of the CYP19 gene and, on the contrary, decreased frequency of the mutant allele and heterozygous and mutant homozygous genotype of the CYP1A2 gene compared to women without proliferative diseases of the uterus.

AXIN1 in Plasma or Serum Is a Potential New Biomarker for Endometriosis

Although endometriosis is considered an inflammatory disease, no reliable diagnostic biomarkers exist for use in clinical practice. The aim was to investigate the inflammatory profile in endometriosis using an exploratory approach of inflammation-related proteins. Patients with laparoscopy-verified endometriosis (N = 172), women with microscopic colitis (N = 50), healthy controls (N = 31), and age-matched controls from the general population (N = 100) were enrolled and questionnaires regarding socioeconomic factors, lifestyle habits, and medical history were completed. Sera from patients and healthy controls were analyzed for 92 inflammatory biomarkers using Proximity Extension Assay technology (PEA). Plasma AXIN1 levels were analyzed in patients with endometriosis and controls from the general population by ELISA. General linear model adjusted for age, Mann–Whitney U-test, and principal component analysis (PCA) were used for statistical calculations. Serum levels of AXIN1 and ST1A1 were increased in endometriosis compared with MC (p < 0.001) and healthy controls (p = 0.001), whereas CXCL9 levels were decreased. Plasma levels of AXIN1 were elevated in endometriosis compared with age-matched controls from the general population (30.0 (17.0–38.0) pg/mL vs. 19.5 (15.0–28.0) pg/mL, p < 0.001). PCA analysis identified four clusters of proteins, where one cluster differed between endometriosis and controls, with strong correlations for AXIN1 and ST1A1. Plasma/serum AXIN1 is an interesting biomarker to be further evaluated in endometriosis.

Identification of zebrafish steroid sulfatase and comparative analysis of the enzymatic properties with human steroid sulfatase

Steroid sulfatase (STS) plays an important role in the regulation of steroid hormones. Metabolism of steroid hormones in zebrafish has been investigated, but the action of steroid sulfatase remains unknown. In this study, a zebrafish sts was cloned, expressed, purified, and characterized in comparison with the orthologous human enzyme. Enzymatic assays demonstrated that similar to human STS, zebrafish Sts was most active in catalyzing the hydrolysis of estrone-sulfate and estradiol-sulfate, among five steroid sulfates tested as substrates. Kinetic analyses revealed that the Km values of zebrafish Sts and human STS differed with respective substrates, but the catalytic efficiency as reflected by the Vmax/Km appeared comparable, except for DHEA-sulfate with which zebrafish Sts appeared less efficient. While zebrafish Sts was catalytically active at 28 °C, the enzyme appeared more active at 37 °C and with similar Km values to those determined at 28 °C. Assays performed in the presence of different divalent cations showed that the activities of both zebrafish and human STSs were stimulated by Ca2+, Mg2+, and Mn2+, and inhibited by Zn+2 and Fe2+. EMATE and STX64, two known mammalian steroid sulafatase inhibitors, were shown to be capable of inhibiting the activity of zebrafish Sts. Collectively, the results obtained indicated that zebrafish Sts exhibited enzymatic characteristics comparable to the human STS, suggesting that the physiological function of STS may be conserved between zebrafish and humans.

Oncological markers CA-125, CA 19-9 and endometriosis

The endometrium tissue is functionally androgen related which plays an important role in women's fertility regulation. In addition recent findings show that endometrium related pathology is closely linked to disrupted androgen biosynthesis and associated regulatory functions. These findings also suggest that androgens might play an important role in endometrium related cancer pathology with significant implications for treatment.Based on these findings, we have assessed 50 female outpatients with endometriosis and the clinical investigations were focused on biochemical serum analysis of DHEAS, oncological markers CA-125 and CA 19-9, estradiol, thyreothropic hormone, and prolactin.The results show significant Spearman correlations of CA-125 and CA 19-9 with dehydroepiandrosterone- DHEA-S (R = 0.52 resp. R = 0.49).This result represents 1st reported finding documenting androgen related increase of CA-125 and CA 19-9 levels as significant markers of endometrium pathology and it is possible to assume that these potential biomarkers could have clinical importance with respect to timely diagnosis.

The sulfatase pathway as estrogen supply in endometrial cancer

OBJECTIVE

Contradictory results are reported about the level of steroid sulfatase (STS), estrogen sulfotransferase (SULT1E1; together, the sulfatase pathway) and aromatase (CYP19A1) in endometrial cancer (EC). The aim of this study was to explore the levels of these enzymes in a well-characterized cohort of EC patients and postmenopausal controls.

MATERIALS AND METHODS

Endometrial tissues from 31 EC patients (21 grade 1 and 10 grade 2-3) and 19 postmenopausal controls were collected. Levels of mRNA (RT-qPCR) and protein (immunohistochemistry) were determined. STS enzyme activity was measured by HPLC, whereas SULT1E1 enzyme activity was determined using a novel method based on liquid chromatography-mass spectrometry (LC-MS/MS).

RESULTS

No significant differences in STS, SULT1E1 mRNA or protein levels and STS:SULT1E1 ratio were found. STS enzyme activity and STS:SULT1E1 activity ratio were significantly decreased in ECs compared with controls. CYP19A1 mRNA levels were lower in ECs than in controls.

CONCLUSION

A novel highly sensitive and accurate protocol to assess SULT1E1 activity is presented. STS enzyme activity and the STS:SULT1E1 activity ratio seem to be lower in ECs than in controls. STS is an important route for estrogen supply in endometrial cells.

Blood steroids are associated with prognosis and fat distribution in endometrial cancer

BACKGROUND

Despite being a hormone dependent cancer, there is limited knowledge regarding the relation between level of steroids in blood and prognosis for endometrial cancer (EC) patients.

METHODS

In this study we investigated plasma levels of 19 steroids using liquid-chromatography tandem mass-spectrometry in 38 postmenopausal EC patients, 19 with long, and 19 with short survival. We explored if estradiol levels were associated with specific abdominal fat distribution patterns and if transcriptional alterations related to estradiol levels could be observed in tumor samples.

RESULTS

The plasma steroid levels for DHEA, DHEAS, progesterone, 21 OH progesterone and E1S were significantly increased (all p < 0.05) in patients with long survival compared to short. Estradiol levels were significantly positively correlated with visceral fat percentage (p = 0.035), and an increased expression of genes involved in estrogen related signaling was observed in tumors from patients with high estradiol levels in plasma.

CONCLUSION

Several of the identified plasma steroids represent promising biomarkers in EC patients. The association between increased estradiol levels and a high percentage of visceral fat indicates that visceral fat is a larger contributor to estradiol production compared to subcutaneous fat in this population.

Endometrial Intracrinology: Oestrogens, Androgens and Endometrial Disorders

Peripheral tissue metabolism of steroids (intracrinology) is now accepted as a key way in which tissues, such as the endometrium, can utilise inactive steroids present in the blood to respond to local physiological demands and 'fine-tune' the activation or inhibition of steroid hormone receptor-dependent processes. Expression of enzymes that play a critical role in the activation and inactivation of bioactive oestrogens (E1, E2) and androgens (A4, T, DHT), as well as expression of steroid hormone receptors, has been detected in endometrial tissues and cells recovered during the menstrual cycle. There is robust evidence that increased expression of aromatase is important for creating a local microenvironment that can support a pregnancy. Measurement of intra-tissue concentrations of steroids using liquid chromatography⁻tandem mass spectrometry has been important in advancing our understanding of a role for androgens in the endometrium, acting both as active ligands for the androgen receptor and as substrates for oestrogen biosynthesis. The emergence of intracrinology, associated with disordered expression of key enzymes such as aromatase, in the aetiology of common women's health disorders such as endometriosis and endometrial cancer has prompted renewed interest in the development of drugs targeting these pathways, opening up new opportunities for targeted therapies and precision medicine.

Synthesis and structure-activity relationships of 2- and/or 4-halogenated 13β- and 13α-estrone derivatives as enzyme inhibitors of estrogen biosynthesis

Ring A halogenated 13α-, 13β-, and 17-deoxy-13α-estrone derivatives were synthesised with N-halosuccinimides as electrophile triggers. Substitutions occurred at positions C-2 and/or C-4. The potential inhibitory action of the halogenated estrones on human aromatase, steroid sulfatase, or 17β-hydroxysteroid dehydrogenase 1 activity was investigated via in vitro radiosubstrate incubation. Potent submicromolar or low micromolar inhibitors were identified with occasional dual or multiple inhibitory properties. Valuable structure–activity relationships were established from the comparison of the inhibitory data obtained. Kinetic experiments performed with selected compounds revealed competitive reversible inhibition mechanisms against 17β-hydroxysteroid dehydrogenase 1 and competitive irreversible manner in the inhibition of the steroid sulfatase enzyme.

Intracrine Regulation of Estrogen and Other Sex Steroid Levels in Endometrium and Non-gynecological Tissues; Pathology, Physiology, and Drug Discovery

Our understanding of the intracrine (or local) regulation of estrogen and other steroid synthesis and degradation expanded in the last decades, also thanks to recent technological advances in chromatography mass-spectrometry. Estrogen responsive tissues and organs are not passive receivers of the pool of steroids present in the blood but they can actively modify the intra-tissue steroid concentrations. This allows fine-tuning the exposure of responsive tissues and organs to estrogens and other steroids in order to best respond to the physiological needs of each specific organ. Deviations in such intracrine control can lead to unbalanced steroid hormone exposure and disturbances. Through a systematic bibliographic search on the expression of the intracrine enzymes in various tissues, this review gives an up-to-date view of the intracrine estrogen metabolisms, and to a lesser extent that of progestogens and androgens, in the lower female genital tract, including the physiological control of endometrial functions, receptivity, menopausal status and related pathological conditions. An overview of the intracrine regulation in extra gynecological tissues such as the lungs, gastrointestinal tract, brain, colon and bone is given. Current therapeutic approaches aimed at interfering with these metabolisms and future perspectives are discussed.

Variants associating with uterine leiomyoma highlight genetic background shared by various cancers and hormone-related traits

Uterine leiomyomas are common benign tumors of the myometrium. We performed a meta-analysis of two genome-wide association studies of leiomyoma in European women (16,595 cases and 523,330 controls), uncovering 21 variants at 16 loci that associate with the disease. Five variants were previously reported to confer risk of various malignant or benign tumors (rs78378222 in TP53, rs10069690 in TERT, rs1800057 and rs1801516 in ATM, and rs7907606 at OBFC1) and four signals are located at established risk loci for hormone-related traits (endometriosis and breast cancer) at 1q36.12 (CDC42/WNT4), 2p25.1 (GREB1), 20p12.3 (MCM8), and 6q26.2 (SYNE1/ESR1). Polygenic score for leiomyoma, computed using UKB data, is significantly correlated with risk of cancer in the Icelandic population. Functional annotation suggests that the non-coding risk variants affect multiple genes, including ESR1. Our results provide insights into the genetic background of leiomyoma that are shared by other benign and malignant tumors and highlight the role of hormones in leiomyoma growth.

Uterine leiomyomas are common benign tumors. Here, a meta-analysis of two European leiomyoma GWAS uncovers 21 leiomyoma risk variants at 16 loci, providing evidence of genetic overlap between leiomyoma and various benign and malignant tumors and highlighting the role of estrogen in tumor growth.

Development of an Image-Guided Orthotopic Xenograft Mouse Model of Endometrial Cancer with Controllable Estrogen Exposure

Endometrial cancer (EC) is the most common gynaecological malignancy in Western society and the majority of cases are estrogen dependent. While endocrine drugs proved to be of insufficient therapeutic value in the past, recent clinical research shows promising results by using combinational regimens and pre-clinical studies and identified potential novel endocrine targets. Relevant pre-clinical models can accelerate research in this area. In the present study we describe an orthotopic and estrogen dependent xenograft mouse model of EC. Tumours were induced in one uterine horn of female athymic nude mice using the well-differentiated human endometrial adenocarcinoma Ishikawa cell line—modified to express the luciferase gene for bioluminescence imaging (BLI). BLI and contrast-enhanced computed-tomograph (CE-CT) were used to measure non-invasive tumour growth. Controlled estrogen exposure was achieved by the use of MedRod implants releasing 1.5 μg/d of 17β-estradiol (E2) in ovariectomized mice. Stable E2 serum concentration was demonstrated by LC-MS/MS. Induced tumours were E2 responsive as increased tumour growth was observed in the presence of E2 but not placebo, assessed by BLI, CE-CT, and tumour weight at sacrifice. Metastatic spread was assessed macroscopically by BLI and histology and was seen in the peritoneal cavity, in the lymphovascular space, and in the thoracic cavity. In conclusion, we developed an orthotopic xenograft mouse model of EC that exhibits the most relevant features of human disease, regarding metastatic spread and estrogen dependency. This model offers an easy to manipulate estrogen dosage (by simply adjusting the MedRod implant length), image-guided monitoring of tumour growth, and objectively measurable endpoints (including tumour weight). This is an excellent in vivo tool to further explore endocrine drug regimens and novel endocrine drug targets for EC.

Two independent sulfation processes regulate mouth-form plasticity in the nematode Pristionchus pacificus

Sulfation of biomolecules, like phosphorylation, is one of the most fundamental and ubiquitous biochemical modifications with important functions during detoxification. This process is reversible, involving two enzyme classes: a sulfotransferase, which adds a sulfo group to a substrate; and a sulfatase that removes the sulfo group. However, unlike phosphorylation, the role of sulfation in organismal development is poorly understood. In this study, we find that two independent sulfation events regulate the development of mouth morphology in the nematode Pristionchus pacificus. This nematode has the ability to form two alternative mouth morphologies depending on environmental cues, an example of phenotypic plasticity. We found that, in addition to a previously described sulfatase, a sulfotransferase is involved in regulating the mouth-form dimorphism in P. pacificus However, it is unlikely that both of these sulfation-associated enzymes act upon the same substrates, as they are expressed in different cell types. Furthermore, animals mutant in genes encoding both enzymes show condition-dependent epistatic interactions. Thus, our study highlights the role of sulfation-associated enzymes in phenotypic plasticity of mouth structures in Pristionchus.

Blocking 17β-hydroxysteroid dehydrogenase type 1 in endometrial cancer: a potential novel endocrine therapeutic approach

The enzyme type 1 17β-hydroxysteroid dehydrogenase (17β-HSD-1), responsible for generating active 17β-estradiol (E2) from low-active estrone (E1), is overexpressed in endometrial cancer (EC), thus implicating an increased intra-tissue generation of E2 in this estrogen-dependent condition. In this study, we explored the possibility of inhibiting 17β-HSD-1 and impairing the generation of E2 from E1 in EC using in vitro, in vivo, and ex vivo models. We generated EC cell lines derived from the well-differentiated endometrial adenocarcinoma Ishikawa cell line and expressing levels of 17β-HSD-1 similar to human tissues. In these cells, HPLC analysis showed that 17β-HSD-1 activity could be blocked by a specific 17β-HSD-1 inhibitor. In vitro, E1 administration elicited colony formation similar to E2, and this was impaired by 17β-HSD-1 inhibition. In vivo, tumors grafted on the chicken chorioallantoic membrane (CAM) demonstrated that E1 upregulated the expression of the estrogen responsive cyclin A similar to E2, which was impaired by 17β-HSD-1 inhibition. Neither in vitro nor in vivo effects of E1 were observed using 17β-HSD-1-negative cells (negative control). Using a patient cohort of 52 primary ECs, we demonstrated the presence of 17β-HSD-1 enzyme activity (ex vivo in tumor tissues, as measured by HPLC), which was inhibited by over 90% in more than 45% of ECs using the 17β-HSD-1 inhibitor. Since drug treatment is generally indicated for metastatic/recurrent and not primary tumor, we next demonstrated the mRNA expression of the potential drug target, 17β-HSD-1, in metastatic lesions using a second cohort of 37 EC patients. In conclusion, 17β-HSD-1 inhibition efficiently blocks the generation of E2 from E1 using various EC models. Further preclinical investigations and 17β-HSD-1 inhibitor development to make candidate compounds suitable for the first human studies are awaited. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Modulation of estrogen synthesis and metabolism by phytoestrogens in vitro and the implications for women's health

Phytoestrogens are increasingly used as dietary supplements due to their suggested health promoting properties, but also by women for breast enhancement and relief of menopausal symptoms. Generally, phytoestrogens are considered to exert estrogenic activity via estrogen receptors (ERs), but they may also affect estrogen synthesis and metabolism locally in breast, endometrial and ovarian tissues. Considering that accurate regulation of local hormone levels is crucial for normal physiology, it is not surprising that interference with hormonal synthesis and metabolism is associated with a wide variety of women's health problems, varying from altered menstrual cycle to hormone-dependent cancers. Yet, studies on phytoestrogens have mainly focused on ER-mediated effects of soy-derived phytoestrogens, with less attention paid to steroid synthesis and metabolism or other phytoestrogens. This review aims to evaluate the potential of phytoestrogens to modulate local estrogen levels and the implications for women's health. For that, an overview is provided of the effects of commonly used phytoestrogens, i.e. 8-prenylnaringenin, biochanin A, daidzein, genistein, naringenin, resveratrol and quercetin, on estrogen synthesizing and metabolizing enzymes in vitro. The potential implications for women's health are assessed by comparing the in vitro effect concentrations with blood concentrations that can be found after intake of these phytoestrogens. Based on this evaluation, it can be concluded that high-dose supplements with phytoestrogens might affect breast and endometrial health or fertility in women via the modulation of steroid hormone levels. However, more data regarding the tissue levels of phytoestrogens and effect data from dedicated, tissue-specific assays are needed for a better understanding of potential risks. At least until more certainty regarding the safety has been established, especially young women would better avoid using supplements containing high doses of phytoestrogens.

The Importance of Steroid Uptake and Intracrine Action in Endometrial and Ovarian Cancers

Endometrial and ovarian cancers predominately affect women after menopause, and are more frequently observed in developed countries. These are considered to be hormone-dependent cancers, as steroid hormones, and estrogens in particular, have roles in their onset and progression. After the production of estrogens in the ovary has ceased, estrogen synthesis occurs in peripheral tissues. This depends on the cellular uptake of estrone-sulfate and dehydroepiandrosterone-sulfate, as the most important steroid precursors in the plasma of postmenopausal women. The uptake through transporter proteins, such as those of the organic anion-transporting polypeptide (OATP) and organic anion-transporter (OAT) families, is followed by the synthesis and action of estradiol E2. Here, we provide an overview of the current understanding of this intracrine action of steroid hormones, which depends on the availability of the steroid precursors and transmembrane transporters for precursor uptake, along with the enzymes for the synthesis of E2. The data is also provided relating to the selected transmembrane transporters from the OATP, OAT, SLC51, and ABC-transporter families, and the enzymes involved in the E2-generating pathways in cancers of the endometrium and ovary. Finally, we discuss these transporters and enzymes as potential drug targets.

Involvement of 17β-hydroxysteroid dehydrogenase type gene 1 937 A>G polymorphism in infertility in Polish Caucasian women with endometriosis

Purpose

Endometriosis is considered to be an estrogen-related chronic inflammatory disease. The 17β-hydroxysteroid dehydrogenase 1 (HSD17B1) converts estrone to 17β estradiol. The role of HSD17B1 937 A>G (rs605059) single nucleotide polymorphism (SNP) in development of endometriosis is still disputable. This study evaluated the association of the HSD17B1 937 A>G (rs605059) SNP with infertile women affected by endometriosis from Polish Caucasian population.

Methods

The genotyping of cases (n = 290) and fertile women (n = 410) was conducted by high-resolution melting curve analysis.

Results

Statistical analysis demonstrated that the HSD17B1 937 A>G SNP is associated with endometriosis in stages I and II. The p_trend and p_allelic values calculated for the HSD17B1 937 A>G polymorphism were statistically significant and were equal to 0.001 and 0.0009, respectively. There was a significant association for the dominant model: (AG + GG vs AA) OR = 1.973 (95% CI = 1.178–3.304), p = 0.009, and for the recessive model: (GG vs AG + AA) OR = 1.806 (95% CI = 1.178–2.770), p = 0.006. However, we did not find statistical association of HSD17B1 937 A>G polymorphism with all infertile women with endometriosis or infertile women with endometriosis in stages III and IV.

Conclusion

Our genetic study demonstrated HSD17B1 937 G variant as a risk factor for infertility in women with stage I and II endometriosis in Polish Caucasian patients.

Electronic supplementary material

The online version of this article (doi:10.1007/s10815-017-0911-9) contains supplementary material, which is available to authorized users.

Clinical significance of the estrogen-modifying enzymes steroid sulfatase and estrogen sulfotransferase in epithelial ovarian cancer

17β-estradiol (E2) can contribute to the progression of epithelial ovarian cancer (EOC). Although the majority of patients with EOC are postmenopausal woman, when de novo estrogen production in the ovary has ceased, ovarian cancer cells remain exposed to estrogens synthesized locally in the cancer cells from inactive sulfonated steroid hormone precursors-such as estrone sulfate taken up from the circulation via the sulfatase pathway. An abundance of the estrogen-modifying enzymes, including estrogen-activating steroid sulfatase (STS) and estrogen-inactivating estrogen-sulfotransferase (SULT1E1), is important for providing active estrogen to EOC cells. Therefore, the present study determined the levels of SULT1E1, STS and estrogen receptor α (ERα) protein in paraffin-embedded specimens from 206 patients with Federation of Gynecology and Obstetrics stage II–IV EOC treated with debulking surgery and standard platinum-based adjuvant chemotherapy. The levels of STS, SULT1E1 and ERα were assessed by automated quantitative microscopy-based image analysis subsequent to immunohistochemical staining. Significantly higher SULT1E1 levels were observed in better differentiated EOC tumors compared to grade 3 EOC tumors (P=0.001). STS and SULT1E1 levels were positively associated with ERα abundance (P<0.001 and P=0.001, respectively). In advanced stage high-grade serous EOC (HGSOC; n=132), the most frequent and lethal type of ovarian cancer, SULT1E1 expression was significantly associated with a better overall survival rate (hazard ratio 0.66, 95% confidence interval, 0.45–0.94; P=0.005). These results highlight the importance of SULT1E1-mediated estrogen inactivation in EOC, particularly HGSOC. Therefore, targeting the sulfatase pathway is a potential endocrine therapeutic intervention for certain patients with estrogen-responsive EOC.

Structural basis for catalysis at the membrane-water interface

The membrane-water interface forms a uniquely heterogeneous and geometrically constrained environment for enzymatic catalysis. Integral membrane enzymes sample three environments - the uniformly hydrophobic interior of the membrane, the aqueous extramembrane region, and the fuzzy, amphipathic interfacial region formed by the tightly packed headgroups of the components of the lipid bilayer. Depending on the nature of the substrates and the location of the site of chemical modification, catalysis may occur in each of these environments. The availability of structural information for alpha-helical enzyme families from each of these classes, as well as several beta-barrel enzymes from the bacterial outer membrane, has allowed us to review here the different ways in which each enzyme fold has adapted to the nature of the substrates, products, and the unique environment of the membrane. Our focus here is on enzymes that process lipidic substrates. This article is part of a Special Issue entitled: Bacterial Lipids edited by Russell E. Bishop.