Unusual arrangement of catalytic domains in head-to-tail associated homodimer of 6-hydroxymellein synthase, a multifunctional polyketide biosyntheticenzyme
F. Kurosaki et al., Unusual arrangement of catalytic domains in head-to-tail associated homodimer of 6-hydroxymellein synthase, a multifunctional polyketide biosyntheticenzyme, PLANT SCI, 157(2), 2000, pp. 217-223
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 cysteam
ine-SHs at the reaction center with iodoacetoamide and chloroacetyl-CoA, re
spectively. Dissociation and stoichiometric recombination of the unmodified
and the SH-modified enzyme subunits yielded a combination of unmodified-un
modified, unmodified-modified and modified-modified hybrid dimers that toge
ther exhibit 50% activity. In contrast, hybrid dimers obtained by reconstru
ction of the two modified enzymes showed essentially no catalytic activity.
These results suggest that the two subunits of 6-hydroxymellein synthase a
re aligned in head-to-tail orientation to organize two reaction centers whi
ch are comprised of a cysteine and a complementary cysteamine SH group, bel
onging to and contributed from the same subunit in the homodimer structure.
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