Biomedical subjects

Douglas Van Hoewyk

Publications and source records attributed to Douglas Van Hoewyk.

3 recordsLinked to original sources

PubMed2006

Biogenesis of iron-sulfur cluster proteins in plastids.

Iron-sulfur (Fe-S) clusters are co-factors of proteins that perform a number of biological roles, including electron transfer, redox and non-redox catalysis, regulation of gene expression, and as sensors within all living organisms, prokaryotes and eukaryotes. These clusters are thought to be among the oldest structures found in biological cells. In chloroplasts, Fe-S clusters play a key role in photosynthetic electron transport as well as nitrogen and sulfur assimilation. The capacity of the Fe atom in Fe-S clusters to take up an electron reversibly provides the required electron carrier capacity in these pathways. Iron and sulfur limitation both affect plant primary production and growth. It has long been known that iron deficiency leads to defects in photosynthesis and bleaching in young leaves, phenomena that are closely linked to a defect in chloroplastic photosystem-I (PSI) accumulation, a major Fe-S containing protein complex in plants. Although the functional importance of Fe-S cluster proteins is evident and isolated chloroplasts have been shown to be able to synthesize their own Fe-S clusters, much is yet to be learned about the biosynthesis of Fe-S proteins in plastids. The recent discovery of a NifS-like protein in plastids has hinted to the existence of an assembly machinery related to bacterial Fe-S assembly systems. This chapter aims to summarize what we presently know about the assembly of Fe-S clusters in plants with an emphasis on green plastids.

Bacterial Proteins↗

PubMed2005

Overexpression of AtCpNifS enhances selenium tolerance and accumulation in Arabidopsis.

Selenium (Se) is an essential element for many organisms but is toxic at higher levels. CpNifS is a chloroplastic NifS-like protein in Arabidopsis (Arabidopsis thaliana) that can catalyze the conversion of cysteine into alanine and elemental sulfur (S0) and of selenocysteine into alanine and elemental Se (Se0). We overexpressed CpNifS to investigate the effects on Se metabolism in plants. CpNifS overexpression significantly enhanced selenate tolerance (1.9-fold) and Se accumulation (2.2-fold). CpNifS overexpressors showed significantly reduced Se incorporation into protein, which may explain their higher Se tolerance. Also, sulfur accumulation was enhanced by approximately 30% in CpNifS overexpressors, both on media with and without selenate. Root transcriptome changes in response to selenate mimicked the effects observed under sulfur starvation. There were only a few transcriptome differences between CpNifS-overexpressing plants and wild type, besides the 25- to 40-fold increase in CpNifS levels. Judged from x-ray analysis of near edge spectrum, both CpNifS overexpressors and wild type accumulated mostly selenate (Se(VI)). In conclusion, overexpression of this plant NifS-like protein had a pronounced effect on plant Se metabolism. The observed enhanced Se accumulation and tolerance of CpNifS overexpressors show promise for use in phytoremediation.

Arabidopsis↗

PubMed2003

The Drosophila cell cycle kinase PAN GU forms an active complex with PLUTONIUM and GNU to regulate embryonic divisions.

Early embryonic cell cycles in Drosophila consist of rapidly alternating S and M phases. Three genes, pan gu (png), plutonium (plu), and giant nuclei (gnu) coordinate these early S-M cycles by ensuring adequate Cyclin B protein levels. Mutations in any of these genes result in unregulated DNA replication and a lack of mitosis ("giant nuclei" phenotype). png encodes a serine/threonine protein kinase, and plu and gnu encode small, novel proteins. We show that PNG, PLU, and GNU constitute a novel protein kinase complex that specifically regulates S-M cell cycles. All three proteins are required for PNG kinase activity and are phosphorylated by PNG in vitro. Yeast two-hybrid screening revealed a direct interaction between PNG and PLU, and their co-expression is required for physical association and activation of PNG kinase. Artificial dimerization of PLU via fusion to either GST or FK506 binding protein (in the presence of dimerizing agent) abrogates the requirement for GNU to activate PNG kinase. We propose a model in which GNU normally regulates embryonic cell cycles by promoting transient dimerization of a core PNG/PLU complex, thereby stimulating PNG kinase activity.

Alleles↗