%0 Journal Article
%T Holocarboxylase Synthetase 1 Physically Interacts with Histone H3 in Arabidopsis
%A Xi Chen
%A Hui-Hsien Chou
%A Eve Syrkin Wurtele
%J Scientifica
%D 2013
%I Hindawi Publishing Corporation
%R 10.1155/2013/983501
%X Biotin is a water-soluble vitamin required by all organisms, but only synthesized by plants and some bacterial and fungal species. As a cofactor, biotin is responsible for carbon dioxide transfer in all biotin-dependent carboxylases, including acetyl-CoA carboxylase, methylcrotonyl-CoA carboxylase, and pyruvate carboxylase. Adding biotin to carboxylases is catalyzed by the enzyme holocarboxylase synthetase (HCS). Biotin is also involved in gene regulation, and there is some indication that histones can be biotinylated in humans. Histone proteins and most histone modifications are highly conserved among eukaryotes. HCS1 is the only functional biotin ligase in Arabidopsis and has a high homology with human HCS. Therefore, we hypothesized that HCS1 also biotinylates histone proteins in Arabidopsis. A comparison of the catalytic domain of HCS proteins was performed among eukaryotes, prokaryotes, and archaea, and this domain is highly conserved across the selected organisms. Biotinylated histones could not be identified in vivo by using avidin precipitation or two-dimensional gel analysis. However, HCS1 physically interacts with Arabidopsis histone H3 in vitro, indicating the possibility of the role of this enzyme in the regulation of gene expression. 1. Introduction Biotin is a water-soluble, B-complex vitamin that is required by all organisms [1]. The main role of biotin is to serve as a cofactor for carboxylases [2, 3]. Addition of biotin to carboxylases is catalyzed by holocarboxylase synthetase (HCS) in a two-step ATP-dependent reaction [4]. Based on the crystal structure of BirA, the E. coli HCS [3], the first step produces an intermediate biotinyl-5¡ä-AMP (B-AMP). B-AMP is then transferred to a specific lysine residue of the carboxylase with the release of AMP [5]. Five biotin-dependent proteins have been characterized in plants [3]. One of them is a seed-specific protein SBP65 for biotin storage [6, 7]. The other four are all carboxylases: homomeric acetyl-CoA carboxylase, heteromeric acetyl-CoA carboxylase, geranoyl-CoA carboxylase, and methylcrotonyl-CoA carboxylase [8¨C11]. These enzymes are involved in many important metabolic pathways, such as gluconeogenesis, fatty acid synthesis, and amino acid catabolism [3] (Figure 1). Figure 1: Biotin network in plants. Schematic map of the metabolism associated with biotin. Metabolites¡¯ names are in black text. Red arrows represent the biotinylating actions of HCS on biotin-dependent proteins. Black arrows represent other metabolic reactions characterized in plants. Enzymes identified by direct biochemical
%U http://www.hindawi.com/journals/scientifica/2013/983501/