Abstract
The Lonely Guy (LOG) protein has been identified as a crucial enzyme involved in the production of cytokinins, which are important phytohormones, in plants and plant-interacting organisms. However, C. glutamicum has an isoform (Cg1261) of LOG that contains an extended N-terminal region compared to those of known LOGs, and this type of isoforms are also found in a variety of organisms. Nevertheless, these proteins are considered as lysine decarboxylases, without their functional characterization. To investigate the function of Cg1261, we determined its crystal structure at a resolution of 1.95 Å. Unlike known dimeric LOGs, Cg1261 was found to form a hexamer. The overall shape of the hexamer resembles a trillium flower, in which a twisted dimer constitutes each petal. The dimeric petal is well superposed with known LOG dimers, and its active site conformation is similar to those of LOG dimers, suggesting that the hexameric LOG-like protein also acts as a LOG. Biochemical and in vivo cytokinin production studies on Cg1261 confirms that Cg1261 functions as a cytokinin-activating protein. Phylogenetic tree analysis using 123 LOG-like proteins suggest that the LOG-like proteins can be categorized to the dimeric type-I LOG and the hexameric type-II LOG.
Highlights
The Lonely Guy (LOG) protein has been identified as a crucial enzyme involved in the production of cytokinins, which are important phytohormones, in plants and plant-interacting organisms
A protein from Thermus thermophilus HB8 (Tt1465), which is homologous to Cg1261, was once assigned as a possible lysine decarboxylases (LDCs) before the discovery of its LOG identity[8], and these proteins have been considered as LDCs, without their functional characterization[9,10,11]
Based on the biochemical and in vivo cytokinin production experiments, we propose that Cg1261 is a novel type of LOG and belongs to type II LOGs (CgLOGII)
Summary
The Lonely Guy (LOG) protein has been identified as a crucial enzyme involved in the production of cytokinins, which are important phytohormones, in plants and plant-interacting organisms. C. glutamicum has an isoform (Cg1261) of LOG that contains an extended N-terminal region compared to those of known LOGs, and this type of isoforms are found in a variety of organisms. These proteins are considered as lysine decarboxylases, without their functional characterization. Cg1261 contains an extended N-terminal region compared to those of known LOGs, including CgLOG, and this type of isoforms have been found in a variety of organisms. Comparative analysis of 123 LOG-like proteins suggested that LOG proteins could be divided into two different types, dimeric type I LOGs and hexameric type II LOGs
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