In:
Proceedings of the National Academy of Sciences, Proceedings of the National Academy of Sciences, Vol. 113, No. 37 ( 2016-09-13), p. 10316-10321
Abstract:
Alkyl branching at the β position of a polyketide intermediate is an important variation on canonical polyketide natural product biosynthesis. The branching enzyme, 3-hydroxy-3-methylglutaryl synthase (HMGS), catalyzes the aldol addition of an acyl donor to a β-keto-polyketide intermediate acceptor. HMGS is highly selective for two specialized acyl carrier proteins (ACPs) that deliver the donor and acceptor substrates. The HMGS from the curacin A biosynthetic pathway (CurD) was examined to establish the basis for ACP selectivity. The donor ACP (CurB) had high affinity for the enzyme ( K d = 0.5 μM) and could not be substituted by the acceptor ACP. High-resolution crystal structures of HMGS alone and in complex with its donor ACP reveal a tight interaction that depends on exquisite surface shape and charge complementarity between the proteins. Selectivity is explained by HMGS binding to an unusual surface cleft on the donor ACP, in a manner that would exclude the acceptor ACP. Within the active site, HMGS discriminates between pre- and postreaction states of the donor ACP. The free phosphopantetheine (Ppant) cofactor of ACP occupies a conserved pocket that excludes the acetyl-Ppant substrate. In comparison with HMG-CoA (CoA) synthase, the homologous enzyme from primary metabolism, HMGS has several differences at the active site entrance, including a flexible-loop insertion, which may account for the specificity of one enzyme for substrates delivered by ACP and the other by CoA.
Type of Medium:
Online Resource
ISSN:
0027-8424
,
1091-6490
DOI:
10.1073/pnas.1607210113
Language:
English
Publisher:
Proceedings of the National Academy of Sciences
Publication Date:
2016
detail.hit.zdb_id:
209104-5
detail.hit.zdb_id:
1461794-8
SSG:
11
SSG:
12
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