A 3-hydroxy-3-methylglutaryl-CoA synthase-based probe for the discovery of the acyltransferase-less type I polyketide synthases

Acyltransferase (AT)-less type I polyketide synthases (PKSs) produce complex natural products due to the presence of many unique tailoring enzymes. The 3-hydroxy-3-methylglutaryl coenzyme A synthases (HCSs) are responsible for β-alkylation of the growing polyketide intermediates in AT-less type I PKSs. In this study, we discovered a large group of HCSs, closely associated with the characterized and orphan AT-less type I PKSs through in silico genome mining, sequence and genome neighbourhood network analyses. Using HCS-based probes, the survey of 1207 in-house strains and 18 soil samples from different geographic locations revealed the vast diversity of HCS-containing AT-less type I PKSs. The presence of HCSs in many AT-less type I PKSs suggests their co-evolutionary relationship. This study provides a new probe to study the abundance and diversity of AT-less type I PKSs in the environment and microbial strain collections. Our study should inspire future efforts to discover new polyketide natural products from AT-less type I PKSs.     

XX/XY System of Sex Determination in the Geophilomorph Centipede Strigamia maritima

We show that the geophilomorph centipede Strigamia maritima possesses an XX/XY system of sex chromosomes, with males being the heterogametic sex. This is, to our knowledge, the first report of sex chromosomes in any geophilomorph centipede. Using the recently assembled Strigamia genome sequence, we identified a set of scaffolds differentially represented in male and female DNA sequence. Using quantitative real-time PCR, we confirmed that three candidate X chromosome-derived scaffolds are present at approximately twice the copy number in females as in males. Furthermore, we confirmed that six candidate Y chromosome-derived scaffolds contain male-specific sequences. Finally, using this molecular information, we designed an X chromosome-specific DNA probe and performed fluorescent in situ hybridization against mitotic and meiotic chromosome spreads to identify the Strigamia XY sex-chromosome pair cytologically. We found that the X and Y chromosomes are recognizably different in size during the early pachytene stage of meiosis, and exhibit incomplete and delayed pairing.     

Synthese d'Oligodesoxyribonucleotides sur Support de Gel de Silice par la Methode au Phosphotriester

Abstract

A method of oligonucleotide synthesis was developped on a silica gel support by the phosphotriester approach. Using this method, the nonanucleoside octaphosphate dT(pT)₈ was synthetized in 28% yield.     

EpCAM: Structure and function in health and disease

Injection of tumor cells in mice more than 30 years ago resulted in the discovery of an epithelial antigen, later defined as a cell adhesion molecule (EpCAM). Although EpCAM has since evoked significant interest as a target in cancer therapy, mechanistic insights on the functions of this glycoprotein have been emerging only very recently. This may have been caused by the multitude of functions attributed to the glycoprotein, its localization at different subcellular sites and complex posttranslational modifications. Here, we review how EpCAM modifies cell–cell contact adhesion strength and tissue plasticity, and how it regulates cell proliferation and differentiation. Major knowledge derived from human diseases will be highlighted: Mutant EpCAM that is absent from the cell surface leads to fatal intestinal abnormalities (congenital tufting enteropathy). EpCAM-mediated cell proliferation in cancer may result from signaling (i) via regulated intramembrane proteolysis and/or (ii) the localization and association with binding partners in specialized membrane microdomains. New insight in EpCAM signaling will help to develop optimized cancer therapies and open new avenues in the field of regenerative medicine.     

Studies on the effect of reagent and protein charges on reactivity of the β93 sulfhydryl group of human hemoglobin using selected mutations

The reactivity of the β93 sulfhydryl (SH) group of human oxyhemoglobins with the negatively charged 5,5′-dithiobis(2,2′-nitrobenzoate) and the uncharged 2,2′-dithiodipyridine was determined as a function of pH. Selected mutant hemoglobins having increased oxygen affinity and having residue substitutions altering charge near the SH group (Wood, Malmö, Yakima, Kempsey, Andrew-Minneapolis, Osler, and Chesapeake) were compared to hemoglobin (Hb) A. Although both reagents reacted with GSH at the same rate and with the same enthalpies of activation, the rates with Hb were different and the difference showed a pronounced pH dependence. The charged reagent was sensitive to charges near the SH group; a positive charge increased the rate and a negative one decreased the rate. The uncharged reagent which reacted with Hb A with activation enthalpies similar to those for GSH was insensitive to neighboring charges, but was sensitive to tertiary and quaternary structural changes. The rates obtained with the latter reagent did not correlate with oxygen affinity. The evolutionary aspects of the β93 cysteine in relation to structure and function are reviewed.