Crystallization and preliminary X-ray crystallographic investigations of an unusual type III polyketide synthase PKS18 from Mycobacterium tuberculosis.

The biosynthetic machinery of polyketide synthases involves various sequential enzymatic reactions, such as initiation, elongation and cyclization, to produce polyketides. PKS18 protein from Mycobacterium tuberculosis belongs to the type III polyketide synthase family and displays an unusual starter-unit specificity to catalyze the formation of α-pyrones. This enzyme uses malonyl-CoA to iteratively extend long-chain aliphatic coenzyme A (C₁₂ to C₂₀) molecules, producing triketide and tetraketide pyrone products. In order to aid in understanding the structural basis of this long-chain specificity and to further characterize the enzymatic mechanism of PKS18, the protein has been crystallized. The crystal belongs to the triclinic space group P1, with unit-cell parameters a = 59.9, b = 80.7, c = 99.6 Å, α = 108.2, β = 93.0, γ = 103.7 °. [ABSTRACT FROM AUTHOR]