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1.  Evolved Diversification of a Modular Natural Product Pathway: Apratoxins F and G, Two Cytotoxic Cyclic Depsipeptides from a Palmyra Collection of Lyngbya bouillonii 
A collection of Lyngbya bouillonii from Palmyra Atoll in the Central Pacific, a site several thousand kilometers distant from all previous collections of this chemically prolific species of cyanobacterium, was found to contain two new cancer cell cytotoxins of the apratoxin family. The structures of the new compounds, apratoxins F and G, were determined by 1-D and 2-D NMR techniques in combination with mass spectrometric methods. Stereochemistry was explored using chromatographic analyses of the hydrolytically released fragments in combination with NMR and optical rotation comparisons with known members of the apratoxin family. Apratoxins F and G add fresh insights into the SAR of this family because they incorporate an N-methyl alanine residue at a position where all prior apratoxins have possessed a proline unit, yet they retain high potency as cytotoxins to H-460 cancer cells with IC50 values of 2 and 14 nM, respectively. Additional assays using zone inhibition of cancer cells and clonogenic cells give a comparison of the activities of apratoxin F to apratoxin A. Additionally, the clonogenic studies in combination with MTD studies provided insights as to dosing schedules that should be used for in vivo studies, and preliminary in vivo evaluation validated the predicted in vivo efficacy for apratoxin A. These new apratoxins are illustrative of a mechanism, the modification of an NRPS adenylation domain specificity pocket, for evolving a biosynthetic pathway so as to diversify the suite of expressed secondary metabolites.
PMCID: PMC3521036  PMID: 20512792
Natural Products; Structure Elucidation; Anti-Cancer; Structure-Activity Relationships; Cyanobacteria
2.  Comprehensive predictions of target proteins based on protein-chemical interaction using virtual screening and experimental verifications 
BMC Chemical Biology  2012;12:2.
Identification of the target proteins of bioactive compounds is critical for elucidating the mode of action; however, target identification has been difficult in general, mostly due to the low sensitivity of detection using affinity chromatography followed by CBB staining and MS/MS analysis.
We applied our protocol of predicting target proteins combining in silico screening and experimental verification for incednine, which inhibits the anti-apoptotic function of Bcl-xL by an unknown mechanism. One hundred eighty-two target protein candidates were computationally predicted to bind to incednine by the statistical prediction method, and the predictions were verified by in vitro binding of incednine to seven proteins, whose expression can be confirmed in our cell system.
As a result, 40% accuracy of the computational predictions was achieved successfully, and we newly found 3 incednine-binding proteins.
This study revealed that our proposed protocol of predicting target protein combining in silico screening and experimental verification is useful, and provides new insight into a strategy for identifying target proteins of small molecules.
PMCID: PMC3471015  PMID: 22480302

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