title: Unusual arrangement of catalytic domains in head-to-tail associated homodimer of 6-hydroxymellein synthase, a multifunctional polyketide biosynthetic enzyme.
abstract: 6-Hydroxymellein synthase, a multifunctional polyketide synthetic enzyme in carrot, is organized as a homodimer, and the activity of the synthase was appreciably inhibited upon the specific alkylation of cysteine- and cysteamine-SHs at the reaction center with iodoacetoamide and chloroacetyl-CoA, respectively. Dissociation and stoichiometric recombination of the unmodified and the SH-modified enzyme subunits yielded a combination of unmodified-unmodified, unmodified-modified and modified-modified hybrid dimers that together exhibit 50% activity. In contrast, hybrid dimers obtained by reconstruction of the two modified enzymes showed essentially no catalytic activity. These results suggest that the two subunits of 6-hydroxymellein synthase are aligned in head-to-tail orientation to organize two reaction centers which are comprised of a cysteine and a complementary cysteamine SH group, belonging to and contributed from the same subunit in the homodimer structure.
authors.affiliation: Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Sugitani, 930-0194, Toyama, Japan
authors.initials: F
authors.lastname: Kurosaki
authors.initials: K
authors.lastname: Togashi
authors.initials: M
authors.lastname: Arisawa