Regional assignment and tissue expression of twenty-three expressed sequence tags (ESTs) from human chromosome 5

Mitochondrial NAD(P)+ Transhydrogenase: From Molecular Features to Physiology and Disease

Significance: Proton-translocating NAD(P)⁺ transhydrogenase, also known as nicotinamide nucleotide transhydrogenase (NNT), catalyzes a reversible reaction coupling the protonmotive force across the inner mitochondrial membrane and hydride (H^-, a proton plus two electrons) transfer between the mitochondrial pools of NAD(H) and NADP(H). The forward NNT reaction is a source of NADPH in the mitochondrial matrix, fueling antioxidant and biosynthetic pathways with reductive potential. Despite the greater emphasis given to the net forward reaction, the reverse NNT reaction that oxidizes NADPH also occurs in physiological and pathological conditions. Recent Advances: NNT (dys)function has been linked to various metabolic pathways and disease phenotypes. Most of these findings have been based on spontaneous loss-of-function Nnt mutations found in the C57BL/6J mouse strain (Nnt^C57BL/6J mutation) and disease-causing Nnt mutations in humans. The present review focuses on recent advances based on the mouse Nnt^C57BL/6J mutation. Critical Issues: Most studies associating NNT function with disease phenotypes have been based on comparisons between different strains of inbred mice (with or without the Nnt^C57BL/6J mutation), which creates uncertainties over the actual contribution of NNT in the context of other potential genetic modifiers. Future Directions: Future research might contribute to understanding the role of NNT in pathological conditions and elucidate how NNT regulates physiological signaling through its forward and reverse reactions. The importance of NNT in redox balance and tumor cell proliferation makes it a potential target of new therapeutic strategies for oxidative-stress-mediated diseases and cancer. Antioxid. Redox Signal. 36, 864-884.

Expression of proton-pumping nicotinamide nucleotide transhydrogenase in mouse, human brain and C elegans

Proton-translocating nicotinamide nucleotide transhydrogenase is located in the mitochondrial inner membrane and catalyzes the reduction of NADP(+) by NADH to NADPH and NAD(+). The present investigation describes the expression of the transhydrogenase gene in various mouse organs, subsections of the human brain and Caenorhabditis elegans. In the mouse, the expression was highest in heart tissue (100%) followed by kidney (64%), testis (52%), adrenal gland (41%), liver (35%), pancreas (34%), bladder (26%), lung (25%), ovary (21%) and brain (14%). The expression in brain tissue was further investigated in the human brain which showed a distribution that apparently varied as a function of neuronal density, a result that was supported by estimations of expression in C. elegans using Green Fluorescent Protein (GFP) controlled by the transhydrogenase promoter. GFP-expressing C. elegans lines showed a clear concentration of fluorescence to the gut, the pharyngeal-intestinal valve and certain neurons. It is concluded that the transhydrogenase gene is expressed to various extents in all cell types in mouse, human and C. elegans.

Characterization of a nicotinamide nucleotide transhydrogenase gene from the green alga Acetabularia acetabulum and comparison of its structure with those of the corresponding genes in mouse and Caenorhabditis elegans

Proton-pumping nicotinamide nucleotide transhydrogenase (Nnt) is a membrane-bound enzyme that catalyzes the reversible reduction of NADP(+) by NADH. This reaction is linked to proton translocation across the membrane. Depending on metabolic conditions, the enzyme may be involved in NADPH generation, e.g., for detoxification of peroxides and/or free radicals and protection from ischemic damage. Nnt exists in most prokaryotes and in animal mitochondria. It is composed of 2-3 subunits in bacteria and of a single polypeptide in mitochondria. An open question is whether Nnt exists in any photosynthetic eukaryotes and if so, to which class it belongs. In the present study it is demonstrated that, by cloning and sequencing cDNA and genomic copies of its NNT gene, an ancient alga, Acetabularia acetabulum (Chlorophyta, Dasycladales), contains a nuclear-encoded Nnt. In contrast to photosynthetic bacteria, this algal Nnt is composed of a single polypeptide of the class found in animal mitochondria. Excluding a poly(A) tail, NNT cDNA from A. acetabulum is 3688 bp long, consists of eight exons and spans 17 kb. The NNT gene from mouse was also characterized. Subsequently, the gene organization of the A. acetabulum NNT was compared to those of the homologous mouse (100 kb and 21 exons) and Caenorhabditis elegans (5.1 kb and 18 exons) genes.

RNAs that interact with the fragile X syndrome RNA binding protein FMRP

The Fragile X protein FMRP is an RNA binding protein whose targets are not well known; yet, these RNAs may play an integral role in the disease's etiology. Using a biotinylated-FMRP affinity resin, we isolated RNAs from the parietal cortex of a normal adult that bound FMRP. These RNAs were amplified by differential display (DDRT-PCR) and cloned and their identities determined. Nine candidate RNAs were isolated; five RNAs, including FMR1 mRNA, encoded known proteins. Four others were novel. The specificity of binding was demonstrated for each candidate RNA. The domains required for binding a subset of the RNAs were delineated using FMRP truncation mutant proteins and it was shown that only the KH2 domain was required for binding. Binding occurred independently of homoribopolymer binding to the C-terminal arginine-glycine-rich region (RGG box), suggesting that FMRP may bind multiple RNAs simultaneously.