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Crystal Structure of the Naturally Fused Coral Lipoxygenase and Allene Oxide Synthase
Author(s) -
Gilbert Nathaniel Carson,
Niebuhr Marc,
Tsuruta Hiro,
Bordelon Tee,
Dassey Adam,
Bartlett Sue,
Newcomer Marcia
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.1012.7
Subject(s) - chemistry , oxylipin , linker , membrane , stereochemistry , covalent bond , lipoxygenase , enzyme , biochemistry , organic chemistry , computer science , operating system
A naturally occurring bi‐functional protein from Plexaura homomalla links sequential catalytic activities in an oxylipin biosynthetic pathway. The C‐terminal 8 R ‐lipoxygenase (8‐LO) domain catalyzes the transformation of arachidonic acid (AA) to the corresponding 8 R ‐hydroperoxyeicosatertaenoic acid, and the N‐terminal allene oxide synthase (AOS) domain promotes the conversion of the hydroperoxide intermediate to the product allene oxide (AO). The structures of the independently expressed 8‐LO and AOS domains have been reported, and previous work has indicated that there are three calcium binding sites that upon coordination promote lipid binding. We report here the crystal structure of the full length bi‐functional enzyme in a calcium bound conformation. Small angle X‐ray scattering data indicate that the two catalytic domains that transform AA to AO associate to form a complex that recapitulates the structure of the bi‐functional protein in the absence of their covalent linkage. However, membrane binding experiments indicate that the covalent tether is required for Ca 2+ ‐dependent membrane targeting of the sequential activities. Furthermore, membrane targeting is accompanied by a conformational change as monitored by specific proteolysis of the linker that joins the AOS and 8‐LO domains. Our data support a model in which Ca 2+ ‐dependent membrane binding releases the non‐covalent interactions between the AOS and 8‐LO domains and suggest that the membrane and AOS binding sites on the 8‐LO domain overlap.