Identification of 5-Fluoro-5-Deoxy-Ribulose as a Shunt Fluorometabolite in Streptomyces sp. MA37

A fluorometabolite, 5-fluoro-5-deoxy-D-ribulose (5-FDRul), from the culture broth of the soil bacterium Streptomyces sp. MA37, was identified through a combination of genetic manipulation, chemo-enzymatic synthesis and NMR comparison. Although 5-FDRul has been chemically synthesized before, it was not an intermediate or a shunt product in previous studies of fluorometalism in S. cattleya. Our study of MA37 demonstrates that 5-FDRul is a naturally occurring fluorometabolite, rendering it a new addition to this rare collection of natural products. The genetic inactivation of key biosynthetic genes involved in the fluorometabolisms in MA37 resulted in the increased accumulation of unidentified fluorometabolites as observed from ¹⁹F-NMR spectral comparison among the wild type (WT) of MA37 and the mutated variants, providing evidence of the presence of other new biosynthetic enzymes involved in the fluorometabolite pathway in MA37.

Characterization of the promiscuous N-acyl CoA transferase, LgoC, in legonoxamine biosynthesis

More than 500 siderophores are known to date, but only three were identified to be aryl-containing hydroxamate siderophores, legonoxamines A and B from Streptomyces sp. MA37, and aryl ferrioxamine 2 from Micrococcus luteus KLE1011.

Targeted Dereplication of Microbial Natural Products by High-Resolution MS and Predicted LC Retention Time

A new strategy for the identification of known compounds in Streptomyces extracts that can be applied in the discovery of natural products is presented. The strategy incorporates screening a database of 5555 natural products including 5098 structures from Streptomyces sp., using a high-throughput LCMS data processing algorithm that utilizes HRMS data and predicted LC retention times (t_R) as filters for rapid identification of known compounds in the natural product extract. The database, named StrepDB, contains for each compound the structure, molecular formula, molecular mass, and predicted LC retention time. All identified compounds are annotated and color coded for easier visualization. It is an indirect approach to quickly assess masses (which are not annotated) that may potentially lead to the discovery of new or novel structures. In addition, a spectral database named MbcDB was generated using the ACD/Spectrus DB Platform. MbcDB contains 665 natural products, each with structure, experimental HRESIMS, MS/MS, UV, and NMR spectra. StrepDB was used to screen a mutant Streptomyces albus extract, which led to the identification and isolation of two new compounds, legonmaleimides A and B, the structures of which were elucidated with the aid of MbcDB and spectroscopic techniques. The structures were confirmed by computer-assisted structure elucidation (CASE) methods using ACD/Structure Elucidator Suite. The developed methodology suggests a pipeline approach to the dereplication of extracts and discovery of novel natural products.

Discovery of a Single Monooxygenase that Catalyzes Carbamate Formation and Ring Contraction in the Biosynthesis of the Legonmycins

Pyrrolizidine alkaloids (PAs) are a group of natural products with important biological activities. The discovery and characterization of the multifunctional FAD-dependent enzyme LgnC is now described. The enzyme is shown to convert indolizidine intermediates into pyrrolizidines through an unusual ring expansion/contraction mechanism, and catalyze the biosynthesis of new bacterial PAs, the so-called legonmycins. By genome-driven analysis, heterologous expression, and gene inactivation, the legonmycins were also shown to originate from non-ribosomal peptide synthetases (NRPSs). The biosynthetic origin of bacterial PAs has thus been disclosed for the first time.

Identification of a fluorometabolite from Streptomyces sp. MA37: (2R3S4S)-5-fluoro-2,3,4-trihydroxypentanoic acid

(2R3S4S)-5-Fluoro-2,3,4-trihydroxypentanoic acid (5-FHPA) has been discovered as a new fluorometabolite in the soil bacterium Streptomyces sp. MA37. Exogenous addition of 5-fluoro-5-deoxy-d-ribose (5-FDR) into the cell free extract of MA37 demonstrated that 5-FDR was an intermediate to a range of unidentified fluorometabolites, distinct from fluoroacetate (FAc) and 4-fluorothreonine (4-FT). Bioinformatics analysis allowed identification of a gene cluster (fdr), encoding a pathway to the biosynthesis of 5-FHPA. Over-expression and in vitro assay of FdrC indicated that FdrC is a NAD+ dependent dehydrogenase responsible for oxidation of 5-FDR into 5-fluoro-5-deoxy-lactone, followed by hydrolysis to 5-FHPA. The identity of 5-FHPA in the fermentation broth was confirmed by synthesis of a reference compound and then co-correlation by 19F-NMR and GC-MS analysis. The occurrence of 5-FHPA proves the existence of a new fluorometabolite pathway.

Fluoroacetate biosynthesis from the marine-derived bacterium Streptomyces xinghaiensis NRRL B-24674

Streptomyces xinghaiensis is the first fluorometabolite producing microorganism identified from the marine environment.

Aberrant cholesterol transport and impaired steroidogenesis in Leydig cells lacking estrogen sulfotransferase

Estrogen sulfotransferase (EST) is a cytosolic enzyme that catalyzes the sulfoconjugation and inactivation of estrogens. It is expressed abundantly in the mammalian testes in which it may modulate the activity of locally produced estrogen. We demonstrate here that testicular Leydig cells from mice rendered deficient in EST expression by targeted gene deletion acquire a phenotype of increased cholesterol ester accumulation and impaired steroidogenesis with natural aging or in response to estrogen challenge. Abnormal accumulation of cholesterol ester in the mutant Leydig cells correlated with induced expression of the scavenger receptor type B class I, and cultured EST-deficient but not wild-type Leydig cells avidly uptook high-density lipoprotein cholesterol ester ex vivo. EST-deficient Leydig cells in culture produced 50-70% less testosterone than wild-type cells. This deficiency was reversed by androstenedione but not progesterone supplementation, indicating that reduced activities of 17-alpha-hydroxylase-17, 20-lyase were responsible. This conclusion was corroborated by decreased expression levels of 17-alpha-hydroxylase-17, 20-lyase but not of other key steroidogenic enzymes in the mutant cells. These results suggest that EST plays a physiologic role in protecting Leydig cells from estrogen-induced biochemical lesions and provide an example of critical regulation of tissue estrogen sensitivity by a ligand-transformation enzyme rather than through estrogen receptors.

Estrogen sulfotransferase: discrete and androgen-dependent expression in the male reproductive tract and demonstration of an in vivo function in the mouse epididymis

Estrogen sulfotransferase (EST) catalyzes the sulfoconjugation and inactivation of the steroid hormone estrogen. It is known previously that EST is expressed abundantly in Leydig cells of the testis. We recently have shown that male mice with targeted EST gene disruption developed age related Leydig cell and seminiferous tubule abnormalities as a consequence of increased local estrogen stimulation. In the same study, we also found that epididymal sperm isolated from the mutant mice had significantly reduced motility, but whether this reflected impaired epididymal function or was secondary to the testicular lesions was not known. The purpose of the current study was to investigate if EST is normally present in the mouse epididymis and/or other parts of the male reproductive tract where, as in testis, it may play a role in regulating local estrogen homeostasis. We describe here that EST is expressed in the epithelium of corpus and cauda but not caput regions of the mouse epididymis. It is also expressed in the luminal epithelium and smooth muscle cells of the vas deferens but was present at very low levels, if at all, in the prostate or seminal vesicle/ coagulating gland. Hypophysectomy, castration, and epididymal ligation experiments, together with the use of an androgen receptor antagonist, established that EST expression in the epididymis and vas deferens is critically dependent on pituitary hormone(s) and androgen but not on other factors in the testicular fluid. Administration of exogenous estradiol to mice with surgically ligated epididymis resulted in a more pronounced reduction in sperm motility in EST mutant mice than in wild-type mice. We conclude that EST is discretely expressed and regulated in the male reproductive tract and plays a physiological role in maintaining the functional integrity of the epididymis by regulating luminal estrogen homeostasis.

Targeted disruption of the mouse estrogen sulfotransferase gene reveals a role of estrogen metabolism in intracrine and paracrine estrogen regulation

Elicitation of biological responses by estrogen in target tissues requires the presence of ER as well as receptor-active ligand in the local microenvironment. Though much attention has been devoted to the study of the receptor in estrogen target tissues, the concept is emerging that tissue estrogen sensitivity may also be regulated by ligand availability through metabolic transformation in situ. Here, we show that targeted disruption, in the mouse, of an estrogen metabolic enzyme, estrogen sulfotransferase (EST), causes structural and functional lesions in the male reproductive system. EST catalyzes the sulfoconjugation and inactivation of estrogen and is expressed abundantly in testicular Leydig cells. Although knockout males were fertile and phenotypically normal initially, they developed age-dependent Leydig cell hypertrophy/hyperplasia and seminiferous tubule damage. Development of these lesions in the testis could be recapitulated by exogenous E2 administration in younger knockout mice, suggesting that they arose in older knockout mice from chronic estrogen stimulation. Older knockout mice were also found to have reduced testis and epididymis weights but increased seminal vesicle/coagulating gland weight because of tissue swelling. Furthermore, total and forward sperm motility of older knockout mice was reduced by 60% and 80%, respectively, and these mice produced smaller litters compared with age-matched wild-type males. These findings establish a role for EST in the male reproductive system and indicate that intracrine and paracrine estrogen activity can be modulated by a ligand transformation enzyme under a physiological setting. Thus, inhibition of estrogen metabolic enzymes by environmental chemicals, as has been demonstrated recently for the human EST, may constitute a novel mechanism of endocrine disruption in vivo.

Evaluation of auditory system in preschool children whose mothers had mid-second trimester amniocentesis

A prospective study was conducted in the Otorhinolaryngology department, National University Hospital, Singapore to evaluate the effects of mid-trimester amniocentesis on the auditory system in preschool children of about four years of age. Fifty-nine children whose mothers had mid-second trimester amniocentesis and 63 children (control group) whose mothers did not have amniocentesis in that pregnancy were recruited. The children were subjected to audiological tests to assess hearing impedance abnormalities. The incidence of prematurity, neonatal admissions, ear and respiratory infections, auditory function, speech and language development in children were evaluated because these factors have a bearing on the development of auditory impedance abnormalities. There was no significant increase in the neonatal admission rates, impairment of speech and language development and auditory function in children whose mothers had mid-second trimester amniocentesis compared with the control group whose mothers did not have amniocentesis. An incidental finding in this study was an increased incidence of respiratory illnesses in the children in the amniocentesis group (57.6%) compared with the control group (30.1%). This needs further evaluation with a properly designed study.

[Reorganization of growth-plate-like tissue by isolated chondrocytes in culture]

Growth-plate cartilage is organized into four cellular zones containing resting, proliferating, maturing, and hypertrophic cells. Rabbit chondrocytes were isolated from growth-plate costal cartilage of 4-week-old New Zealand rabbits, the cells (15 x 10(4)) were suspended in 1 ml of Iscove's modified Dulbecco's medium (IMDM) with 10% fetal bovine serum, 50 micrograms ascorbic acid, and 60 micrograms kanamycin (medium A), then transferred to a 15 ml of plastic centrifuge tube, and centrifuged at 1500 rpm for 5 min. The cell pellet was incubated at 37 degrees C under 5% CO2 in air. The cultures reorganized into growth plate-like tissue which could be seen 7-14 days after cell seeding. This growth-plate, histologically, was organized longitudinally into cellular columns and horizontally into four cellular zones containing resting, proliferating, maturing and hypertrophic cells. The hypertrophic cells in the upper were large in size and round or oval in shape, the proliferating and the mature chondrocytes in the lower were small in size and spherical or elongated in shape. These chondrocytes were surrounded by an extensive matrix. Biochemically, DNA content of cultures began to rise on the 2nd day after cell seeding and reached a plateau after 10 days later. The uronic acid content increased from day 4 and reached the maximum on day 15. In contrast in the early culture, alkaline phosphatase activity was extremely low, it began to rise on day 9 and was the highest on day 20. The sequential increase of DNA, uronic acid and alkaline phosphatase contents was analogous to the in vivo changes of growth-plate chondrocytes.