Abstract
In plant cells, heme is synthesized in chloroplasts and transported to various organelles. Furthermore, tetrapyrrole intermediates is presumed as plastid-derived signals that regulate the expression of nuclear photosynthetic genes. Previously, we showed the existence of p22HBP/SOUL gene family in Arabidopsis thaliana that is involved in tetrapyrroles transport in animal cells, and actually one of recombinant proteins could bind heme. Here, we analyzed cytosolic tetrapyrrole binding protein (TBP) of Arabidopsis. Among 4 putative cytosolic TBP genes in database, ORF of 1 gene (At1g78450) contained deletion suggesting this is pseudogene. Using purified recombinant proteins of At1g17100 (TBP17100) and At3g37970 (TBP37970), we performed binding analysis to metal porphyrins. Both proteins showed specific binding to heme, while they non-specifically bound to other metal porphyrins. TBP17100 showed specific binding to protoporphyrin IX, whereas TBP37970 possessed only nonspecific binding. These results suggest that TBP17100 and TBP37970 have distinct functions for cytosolic tetrapyrrole transport in plant cells.
