Cytochrome P450-dependent fatty acid hydroxylases in plants

Abstract

In plants, hydroxy-fatty acid production is mainly the result of enzymatic reactions catalyzed by cytochrome P450 dependent fatty acid hydroxylases. One can distinguish x-hydroxylases that catalyze the hydroxylation of the terminal methyl of aliphatics acids (x position) and sub-terminal or in-chain hydroxylases that oxidize carbons in the chain (x-n position). Since both types of enzymes were discovered about three decades ago, the majority of investigations have focused on the CYP94 and CYP86 families, which mediate x-hydroxylations. The activities of x-hydroxylases in cutin synthesis have been clearly established, but the studies of LCR (LACERATA) and att1 (aberrant induction of type three genes), which are the first Arabidopsis thaliana mutants with alterations in coding sequences of CYP86A8 and CYP86A2, show that these types of x-hydroxylases can be involved in many aspects of plant development. The existence of different x-hydroxylases in plants with distinct regulation patterns suggests that these enzymes mediate diverse biological processes. Much less information concerning in-chain hydroxylases is available despite the fact that they were initially reported along with x-hydroxylases. This lack of information might be explained by the very few examples of sub-terminal hydroxyfatty acids described in plants. We present here the best characterized fatty acid hydroxylases and we discuss their possible roles in plant defense and development, fatty acid catabolism, plant reproduction and detoxification.

Regioselective Biocatalytic Hydroxylation of Fatty Acids by Cytochrome P450s

“…Nevertheless, a range of catalysts with promising regioselectivities originates from other sources [32]. The eukaryotic classes CYP1 and CYP2 demonstrate in-chain hydroxylation with sometimes outstanding selectivity, such as the strict ω-6 hydroxylation of C12:0 by Cyp2M1 from Oncorhynchus mykiss (Rainbow trout; Table 5, entry 24) [83].…”

“…The eukaryotic classes CYP1 and CYP2 demonstrate in-chain hydroxylation with sometimes outstanding selectivity, such as the strict ω-6 hydroxylation of C12:0 by Cyp2M1 from Oncorhynchus mykiss (Rainbow trout; Table 5, entry 24) [83]. CYP classes from plants, that perform in-chain hydroxylation of fatty acids include CYP77, CYP81, CYP96, CYP703, and CYP709 [32,33]. Two selective orthologues that were heterologously expressed in yeast are CYP703 from Arabidopsis thaliana (mainly active on carbon number 7 of C10:0, C12:0, and C14:0) [98] and CYP81B1 from Helianthus tuberosus (carbon number 7 and 8 in C10:0, C12:0, and C14:0) [99].…”

“…A range of CYP classes have evolved to perform this challenging reaction, including orthologues from eukaryotic sources such as enzymes from vertebrates (CYP4), plants (CYP76, CYP78, CYP86, CYP94, CYP96) [32], and fungi (CYP52), as well as prokaryotic sources (CYP153) [36]. In addition to these P450s that are naturally active towards the terminus, other enzymes were converted into ω-hydroxylases by site-directed mutagenesis and directed evolution.…”

“…Substrate concentrations, stereo-, and the regio-selectivity achieved by wildtype enzymes and variants are summarized and only variants with described sequences and reasonable overexpression level are considered. Other systems were described elsewhere [19,20,[31][32][33][34][35]. Active site geometries and the amino acids that are responsible for the enzymes regio-selectivity are discussed in the individual chapters.…”

The Cytochrome P450 Enzyme CYP96A15 Is the Midchain Alkane Hydroxylase Responsible for Formation of Secondary Alcohols and Ketones in Stem Cuticular Wax of Arabidopsis

“…Examples include hydroxylation steps in the biosynthesis of terpenoids (Kim et al, 2005;Morikawa et al, 2006;Mau and Croteau, 2006), alkaloids (Collu et al, 2001(Collu et al, , 2002, and phenolics (Whitbred and Schuler, 2000;Ehlting et al, 2006). Most notably, cytochrome P450 enzymes have recently also been shown to be involved in the synthesis of cutin monomers by hydroxylating methyl groups at the v-chain terminus of fatty acids (for review, see Kandel et al, 2006). It stands to reason, then, that a cytochrome P450 enzyme could also be involved in the hydroxylation of alkanes during wax biosynthesis.…”