TY - JOUR

T1 - Sea Urchin Polyketide Synthase SpPks1 Produces the Naphthalene Precursor to Echinoderm Pigments

AU - Li, Feng

AU - Lin, Zhenjian

AU - Torres, Joshua P.

AU - Hill, Eric A.

AU - Li, Dehai

AU - Townsend, Craig A.

AU - Schmidt, Eric W.

PY - 2022

Y1 - 2022

N2 - Nearly every animal species on Earth contains a unique polyketide synthase (PKS) encoded in its genome, yet no animal-Glade PKS has been biochemically characterized, and even the chemical products of these ubiquitous enzymes are known in only a few cases. The earliest animal genome-encoded PKS gene to be identified was SpPks1 from sea urchins. Previous genetic knockdown experiments implicated SpPks1 in synthesis of the sea urchin pigment echinochrome. Here, we express and purify SpPks1, performing biochemical experiments to demonstrate that the sea urchin protein is responsible for the synthesis of 2-acetyl-1,3,6,8- tetrahydroxynaphthalene (ATHN). Since ATHN is a plausible precursor of echinochromes, this result defines a biosynthetic pathway to the ubiquitous echinoderm pigments and rewrites the previous hypothesis for echinochrome biosynthesis. Truncation experiments showed that, unlike other type I iterative PKSs so far characterized, SpPks1 produces the naphthalene core using solely ketoacylsynthase (KS), acyltransferase, and acyl carrier protein domains, delineating a unique class of animal nonreducing aromatic PKSs (aPKSs). A series of amino acids in the KS domain define the family and are likely crucial in cyclization activity. Phylogenetic analyses indicate that SpPks1 and its homologs are widespread in echinoderms and their closest relatives, the acorn worms, reinforcing their fundamental importance to echinoderm biology. While the animal microbiome is known to produce aromatic polyketides, this work provides biochemical evidence that animals themselves also harbor ancient, convergent, dedicated pathways to carbocyclic aromatic polyketides. More fundamentally, biochemical analysis of SpPks1 begins to define the vast and unexplored biosynthetic space of the ubiquitous animal PKS family.

AB - Nearly every animal species on Earth contains a unique polyketide synthase (PKS) encoded in its genome, yet no animal-Glade PKS has been biochemically characterized, and even the chemical products of these ubiquitous enzymes are known in only a few cases. The earliest animal genome-encoded PKS gene to be identified was SpPks1 from sea urchins. Previous genetic knockdown experiments implicated SpPks1 in synthesis of the sea urchin pigment echinochrome. Here, we express and purify SpPks1, performing biochemical experiments to demonstrate that the sea urchin protein is responsible for the synthesis of 2-acetyl-1,3,6,8- tetrahydroxynaphthalene (ATHN). Since ATHN is a plausible precursor of echinochromes, this result defines a biosynthetic pathway to the ubiquitous echinoderm pigments and rewrites the previous hypothesis for echinochrome biosynthesis. Truncation experiments showed that, unlike other type I iterative PKSs so far characterized, SpPks1 produces the naphthalene core using solely ketoacylsynthase (KS), acyltransferase, and acyl carrier protein domains, delineating a unique class of animal nonreducing aromatic PKSs (aPKSs). A series of amino acids in the KS domain define the family and are likely crucial in cyclization activity. Phylogenetic analyses indicate that SpPks1 and its homologs are widespread in echinoderms and their closest relatives, the acorn worms, reinforcing their fundamental importance to echinoderm biology. While the animal microbiome is known to produce aromatic polyketides, this work provides biochemical evidence that animals themselves also harbor ancient, convergent, dedicated pathways to carbocyclic aromatic polyketides. More fundamentally, biochemical analysis of SpPks1 begins to define the vast and unexplored biosynthetic space of the ubiquitous animal PKS family.

KW - BIOSYNTHETIC GENE-CLUSTER

KW - ENGINEERED BIOSYNTHESIS

KW - KETOREDUCTASE DOMAINS

KW - AROMATIC POLYKETIDE

KW - QUINONE PIGMENTS

KW - CLAISEN CYCLASE

KW - IDENTIFICATION

KW - SPECIFICITY

KW - EXPRESSION

KW - PROVIDE

U2 - 10.1021/jacs.2c01416

DO - 10.1021/jacs.2c01416

M3 - Journal article

C2 - 35588530

VL - 144

SP - 9363−9371

JO - Journal of the American Chemical Society

JF - Journal of the American Chemical Society

SN - 0002-7863

ER -