Crystallization and preliminary crystallographic analysis of an acridone-producing novel multifunctional type III polyketide synthase from Huperzia serrata

Abstract

Polyketide synthase 1 (PKS1) from Huperzia serrata is a plant-specific type III polyketide synthase that shows an unusually versatile catalytic potential, producing various aromatic tetraketides, including chalcones, benzophenones, phlorogulucinols and acridones. Recombinant H. serrata PKS1 expressed in Escherichia coli was crystallized using the hanging-drop vapour-diffusion method. The crystals belonged to space group I222 or I2(1)2(1)2(1), with unit-cell parameters a = 73.3, b = 85.0, c = 137.7 A, alpha = beta = gamma = 90.0 degrees. Diffraction data were collected to 2.0 A resolution using synchrotron radiation at BL24XU of SPring-8.

Figure 1

Proposed mechanism for the formation of (a) naringenin chalcone from 4-coumaroyl-CoA catalyzed by regular CHS and H. serrata PKS1, (b) 4-methoxy-2′,4′,6′-trihydroxychalcone from 4-methoxycinnamoyl-CoA catalyzed by H. serrata PKS1 and (c) 1,3-dihydroxy-N-methylacridone from N-methylanthraniloyl-CoA catalyzed by R. graveolens ACS and H. serrata PKS1.

Figure 2

Crystals of H. serrata PKS1 grown by the hanging-drop method. The dimensions of the crystals were approximately 0.15 × 0.05 × 0.05 mm.