Unraveling the principles of catalytic diversity in the carotenoid oxygenase superfamily

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With the support of the Chemistry of Life Processes Program in the Division of Chemistry, Dr. Philip Kiser from the University of California, Irvine is studying a family of enzymes known as carotenoid cleavage dioxygenases (CCDs). These enzymes have a highly conserved 4-His iron center and exhibit a remarkably diverse set of catalytic activities. They are well known to oxidatively split carotenoids, which are colored compounds found abundantly in nature including in many foods. Beyond this oxidation reaction, certain CCDs catalyze other reactions involving carotenoids and their derivatives and also non-carotenoid molecules. These reactions are involved in several important biological processes including the production of universal light-sensing molecules, breakdown of spent plant matter, and generation of signaling molecules critical for plant and animal physiology. As such, control of CCD function has long been of interest in a variety of applied research fields including agriculture, horticulture, medicine, and biofuel production. Despite their importance, many critical gaps in knowledge remain regarding how CCDs achieve such varied activities, which consequently has limited our ability to control or modify their function. This research project seeks to provide a molecular level understanding of how CCDs achieve their diverse activities. The new knowledge may open new avenues for controlling the CCD activity using small molecule modulators or by rational alteration of their molecular structure. The participation of graduate and undergraduate students from underrepresented minority groups and those with military service in this research will help achieve a broader educational goal of promoting the entry of such individuals into STEM-fields.The primary focus of this research project is to elucidate the determinants of the varied activities that are exhibited by CCDs. The first aim is to uncover the mechanism by which CCDs trigger dioxygen reactivity using a variety of sophisticated spectroscopic techniques. The second aim will employ high-resolution X-ray crystallography to uncover the active site properties that allow certain CCDs to carry out trans-cis isomerization of carotenoid substrates. The third aim focuses on probing the breadth and mechanism of CCD substrate specificity by rational mutagenesis and the CCD activities found in archaea that occupy diverse ecological niches. Overall, this research will advance the understanding of the catalytic diversity of CCDs and will provide novel insights into their evolution and biological functions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.