homologs. Finally, phylogenetic analysis reinforces the unusual
evolutionary history of these enzymes first suggested by amino
acid sequence alignments. Instead of being related to plant or
red algal enzymes, they form their own distinct branch. This
affiliation is despite the distant relationship between red algae
and diatoms. Examination of hypothetical homologs from the
acromelic acid producing mushroom may enable better insight
into how these enzymes evolved (46). In addition, the detailed
understanding of DabA described here may help inform the
creation of PCR based assays that can detect DabA expression in
the environment to serve as early warning systems before domoic
acid accumulates to toxic levels. This approach is analogous to
the successful methods used in freshwater neurotoxin monitoring
The SI Appendix includes methods for expression, purification, and muta-
genesis of DabA and KabA. Methodologies for crystallization, activity assays,
and small molecule characterization are available in the SI Appendix. Crys-
tallographic data are available in the Protein Data Bank (see Data De-
position), while the remaining data and methods are present in the SI
ACKNOWLEDGMENTS. We thank G. Louie (Salk Institute) and the staff of
the Advanced Light Source (ALS) at beamlines 8.2.1 and 8.2.2 (Berkeley, CA)
for assistance with data collection, G. Rouse (Scripps Institution of Ocean-
ography) for helpful discussions, and D. Nguyen for assistance with synthesis.
This research was supported by the National Oceanic and Atmospheric
Administration under Award NA19NOS4780181 to B.S.M. and the Life
Science Research Foundation through a Simons Foundation Fellowship to J.R.C.
(
47). Finally, our results reinforce the observation that under-
studied organisms create opportunities to discover new types of
enzyme biocatalysts (48).
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