RRC ID 6300
Author Takahashi S, Ogawa T, Inoue K, Masuda T.
Title Characterization of cytosolic tetrapyrrole-binding proteins in Arabidopsis thaliana.
Journal Photochem Photobiol Sci
Abstract In plant cells, tetrapyrroles are synthesized in plastids and distributed to numerous organelles to function in various vital activities. However, molecular mechanisms of tetrapyrroles trafficking in plant cells are poorly understood. In animal cells, experimental evidence suggests that the p22HBP/SOUL family are cytosolic heme carrier proteins functioning in heme trafficking. In this study, we characterized Arabidopsis cytosolic heme-binding proteins (cHBPs) homologous to the p22HBP/SOUL family. Six homologous genes were identified in the complete genome of Arabidopsis. Deduced amino acid sequences of two genes contained N-terminal amino acid extensions, presumably functioning as signal peptides to organelles. No such extension was observed in the other four genes, but one gene contained a ten-base deletion in its open reading frame, suggesting it maybe a pseudogene. The remaining three genes encoding putative cHBPs, designated cHBP1, cHBP2 and cHBP3, were further analyzed. Semiquantitative RT-PCR analysis showed that cHBP1 was preferentially expressed in leaves, while cHBP2 was predominantly expressed in roots. A tetrapyrrole binding assay using recombinant proteins of cHBP1 and cHBP2 revealed that both cHBPs bind to heme, protoporphyrin IX, and Mg-protoporphyrin IX dimethyl ester with distinct dissociation constants (Kd) of approximately submicro molar concentrations. Low temperature electron spin resonance (ESR) spectra showed that both cHBP1 and cHBP2 bind high-spin type heme. When mixed with apo-horse radish peroxidase (HRP), heme-bound cHBP1 and cHBP2 showed comparable abilities for reconstitution of HRP activity, showing that both cHBPs bind heme reversibly. These results suggest that both cHBP1 and cHBP2 have properties suitable for tetrapyrrole carrier proteins and function in distinct organs in plant cells.
Volume 7(10)
Pages 1216-24
Published 2008-10-1
DOI 10.1039/b802588f
PMID 18846286
MeSH Amino Acid Sequence Arabidopsis / chemistry* Arabidopsis / genetics* Binding Sites Carrier Proteins / chemistry* Carrier Proteins / genetics* Cytosol / chemistry* Electron Spin Resonance Spectroscopy Genes, Plant / genetics Heme-Binding Proteins Hemeproteins / chemistry* Hemeproteins / genetics* Peroxidases / metabolism Recombinant Proteins / chemistry Recombinant Proteins / genetics Reverse Transcriptase Polymerase Chain Reaction Sequence Alignment Temperature Tetrapyrroles / chemistry*
IF 2.831
Times Cited 31
Arabidopsis / Cultured plant cells, genes pdx03746 pda08804 pdx58434 pdx80640 pda13754 pda15291 pda06278 pda02562 pda02954