Structural and catalytic insights into the algal prostaglandin H synthase reveal atypical features of the first non-animal cyclooxygenase

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• 作者：Kü ; lliki Varvas ; Sergo Kasvandik ; Kristella Hansen ; Ivar Jä ; rving ; Indrek Morell ; Nigulas Samel ; ^{nigulas.samel@ttu.ee}
• 关键词：PGHS ; prostaglandin H synthase ; GvPGHS ; Gracilaria vermiculophylla PGHS ; CtPGHS ; Coccotylus truncatus PGHS ; huPGHS ; human PGHS ; AA ; arachidonic acid ; PG ; prostaglandin ; AEA ; arachidonoyl ethanolamide ; AG ; arachidonoylglycerol ; HPETE ; hydroperoxyeicosatetr
• 刊名：Biochimica et Biophysica Acta (BBA)/Molecular and Cell Biology of Lipids
• 出版年：2013
• 出版时间：April, 2013
• 年：2013
• 卷：1831
• 期：4
• 页码：863-871
• 全文大小：1135 K

文摘

Prostaglandin H synthases (PGHSs) have been identified in the majority of vertebrate and invertebrate animals, and most recently in the red alga Gracilaria vermiculophylla. Here we report on the cloning, expression and characterization of the algal PGHS, which shares only about 20 % of the amino acid sequence identity with its animal counterparts, yet catalyzes the conversion of arachidonic acid into prostaglandin-endoperoxides, PGG₂ and PGH₂. The algal PGHS lacks structural elements identified in all known animal PGHSs, such as epidermal growth factor-like domain and helix B in the membrane binding domain. The key residues of animal PGHS, like catalytic Tyr-385 and heme liganding His-388 are conserved in the algal enzyme. However, the amino acid residues shown to be important for substrate binding and coordination, and the target residues for nonsteroidal anti-inflammatory drugs (Arg-120, Tyr-355, and Ser-530) are not found at the appropriate positions in the algal sequences. Differently from animal PGHSs the G. vermiculophylla PGHS easily expresses in Escherichia coli as a fully functional enzyme. The recombinant protein was identified as an oligomeric (evidently tetrameric) ferric heme protein. The preferred substrate for the algal PGHS is arachidonic acid with cyclooxygenase reaction rate remarkably higher than values reported for mammalian PGHS isoforms. Similarly to animal PGHS-2, the algal enzyme is capable of metabolizing ester and amide derivatives of arachidonic acid to corresponding prostaglandin products. Algal PGHS is not inhibited by non-steroidal anti-inflammatory drugs. A single copy of intron-free gene encoding for PGHS was identified in the red algae G. vermiculophylla and Coccotylus truncatus genomes.