Abstract
The breakdown of fatty acids, performed by the beta-oxidation cycle, is crucial for plant germination and sustainability. beta-Oxidation involves four enzymatic reactions. The final step, in which a two-carbon unit is cleaved from the fatty acid, is performed by a 3-ketoacyl-CoA thiolase (KAT). The shortened fatty acid may then pass through the cycle again (until reaching acetoacetyl-CoA) or be directed to a different cellular function. Crystal structures of KAT from Arabidopsis thaliana and Helianthus annuus have been solved to 1.5 and 1.8 A resolution, respectively. Their dimeric structures are very similar and exhibit a typical thiolase-like fold; dimer formation and active site conformation appear in an open, active, reduced state. Using an interdisciplinary approach, we confirmed the potential of plant KATs to be regulated by the redox environment in the peroxisome within a physiological range. In addition, co-immunoprecipitation studies suggest an interaction between KAT and the multifunctional protein that is responsible for the preceding two steps in beta-oxidation, which would allow a route for substrate channeling. We suggest a model for this complex based on the bacterial system.
Highlights
Bidopsis thaliana seeds deficient in -oxidation enzymes are unable to germinate without an external sugar source; they have large and unusual peroxisomes and accumulate C16 –C20 fatty acids [5, 6]. -Oxidation is responsible for the synthesis of jasmonic acid [7] and indole-3-acetic acid via conversion from indole-3-butyric acid [8], which serve as crucial plant hormones regulating plant development and responses to biotic and abiotic stress
AtKAT2 consists of residues 46 – 448 (A) and 47– 448 (B), and HaKAT consists of residues 47– 438 (A) and 45– 438 (B)
To facilitate an easy reference system for the secondary structure elements, the sequences of AtKAT2 and HaKAT were aligned with sequences of other known KAT2 structures, namely from A. thaliana in the inactive form (AtKAT2inactive; PDB code 2C7Y [21]), Homo sapiens (HsKAT; 2IIK), S. cerevisiae (ScKAT; 1AFW [19]), and P. fragi (PfKAT; 1WDK, chains C and D [16]). -Strands and helices (␣ and 310) were defined using PDBsum [50], incorporated, and numbered according to domains
Summary
Type I is 3-ketoacyl-CoA thiolase (EC 2.3.1.16), a catabolic enzyme performing the reverse Claisen condensation reaction involved in, for example, the -oxidation cycle. The first structure of KAT was solved from Saccharomyces cerevisiae (ScKAT) [19, 20] This structure has a typical thiolase-like fold, is a homodimer, and presumably is in an active state. A regulation of -oxidation by redox potential was suggested; they did not produce either a structure of AtKAT2 in an active, reduced state or any results that suggested oxidation taking place within a biologically relevant redox range. We present results demonstrating that the redox state and activity of AtKAT2 are affected under biologically relevant conditions as well as the crystal structures of two plant thiolases, AtKAT2 and sunflower HaKAT (Helianthus annuus (HaKAT)), in a reduced, open, active conformation to high resolution. For completeness we have included in the supplemental material a comparison of the KAT structures presented here with other available peroxisomal type I KAT structures at a structural and substrate binding level
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
