Biotin histones

Figure 26.6. Effect of fucoxanthin on DNA fragmentation in HL-60 cells. HL-60 cells (1 - 105 cells/ml) were incubated with different concentration of fucoxanthin for 24h (A) and different incubation time with 11.3mM fucoxanthin (B). DNA fragmentation was analyzed by sandwich ELISA with biotin labeled anti-histone antibody and peroxidase conjugated anti-DNA antibody.The level of DNA fragmentation was expressed as an enrichment factor defined as absorbance (405 nm) of cells treated with fucoxanthin relative to that of untreated cells. Source Hosokawa et al., 1999.

MetabolicaUy, biotin is of central importance in lipogenesis, gluconeogen-esis, and the catabolism of branched-chain (and other) amino acids. There are two well-characterized biotin-responsive inborn errors of metabolism, which are fatal if untreated holocarboxylase synthetase deficiency and biotinidase deficiency. In addition, biotin induces a number of enzymes, including glu-cokinase and other key enzymes of glycolysis. Biotinylation of histones may be important in regulation of the cell cycle. 

Biotin is the coenzyme in a small number of carboxylation reactions in mammalian metabolism and some decarboxylation and transcarboxylation reactions in bacteria. Although the biotin-dependent enzymes are cytosolic and mitochondrial, about 25% of tissue biotin is found in the nucleus, much of it bound as thioesters to histones. Biotin has two noncoenzyme functions induction of enzyme synthesis and regulation of the cell cycle. 

All four carboxylases use bicarbonate as their one-carbon substrate and, in all, the biotin is covalently linked by an amide bond between the carboxyl of biotin and an epsilon amino group of a lysyl residue in the holocarboxylase synthase (= biotin ligase) that catalyzes the formation of the covalent bond. Biotinylation of histones is involved in regulation of gene transcription and may also play a role in packaging of deoxyribonucleic acid (DNA). Biotin has also been found to inhibit the generation of reactive oxygen species (ROS) by neutrophils in vitro. 

Predominant protein blockers include bovine serum albumin (BSA), nonfat dry milk (NFDM), casein, and fish gelatin. NFDM, used at 0.1 0.5%, is inexpensive but preparations vary in quality. Some NFDM preparations contain histones that interfere with anti-DNA determinations or inhibitors of the biotin (strept)avidin interaction such as biotin itself. Casein is a chief component of NFDM and is often used alone as a blocking agent. 

Figure 10.3 Histones H2A, H3 and H4 are posttranslationally modified. Abbreviations Ac, acetate B, biotin M, methyl P, phosphate U, ubiquitin (data from Kouzarides and Berger 2007 Zempleni et al. 2009). Posttransla-tional modifications in histone H2B are not depicted.

Breakdown of carboxylases leads to the release of biotinylated polypeptides. Biotinidase releases free biotin from these peptides for recycling in the synthesis of new holocarboxylases (cf. biotinidase deficiency by Wolf and Heard 1991). In the 1990s, biotinidase was considered the enzyme that might be responsible for mediating the binding of biotin to histones (Hymes et al. 1995). Clearly, biotinidase has catalytic activity to mediate biotinylation of histones in vitro (Camporeale et al. 2004). However, evidence suggests that HLCS is the enzyme that mediates biotinylation of histones in vivo (Camporeale et al. 2006) and that biotinidase might play a role in the enzymatic removal of biotin from histones (Ballard et al. 2002), which is consistent with their roles in carboxylase metabolism. 

Biotin is also covalently attached to histones, but the abundance of biotinylated histones is low. It is unclear whether the eifects of histone biotinylation in gene repression and genome stability are mediated by histone biotinylation or by interactions of holocarboxylase synthetase with other chromatin proteins. 

Biotin and folic acid (FA) (Figure 23.1) are two members of the water-soluble B complex vitamins. Biotin plays an important role in gene expression, cell signalling and histone biotinylation, and functions as a coenzyme in the tricarboxylic acid (TCA) cycle. It also functions in the metabolism of fatty... 

CRISP, S. E. R. H., CAMPGREALE, G., WHITE, B. R., TGGMBS, C. F., GRIFEIN, J. B., SAID, H. M., ZEMPLENI, J. (2004) Biotin supply affects rates of cell proliferation, biotinylation of carboxylases and histones, and expression of the gene encoding the sodium-dependent multivitamin transporter in JAr choriocarcinoma cells. Eur. J. Nutr., 43, 23-31. 

In 1995, Hymes and Wolf discovered that biotini-dase can act as a biotinyl-transferase biocytin serves as the source of biotin, and histones are specifically biotinylated. Approximately 25% of total cellular biotinidase activity occurs in the nucleus. Zempleni and coworkers demonstrated that the abundance of biotinylated histones varies with the cell cycle, that biotinylated histones are increased approximately twofold compared to quiescent lymphocytes, and that histones are debiotinylated enzymatically in a process that is at least partially catalyzed by biotinidase. These observations suggest that biotin plays a role in regulating DNA transcription and regulation. 

Biotin is also used in the modulation of histone activity. Histones are a family of protdns responsible for packaging DNA in order to form chromosomes. It is believed that attachment of biotin (biotinylation) helps reduce the binding of histones to DNA, thereby allowing DNA replication to occur. 

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