Document Type
Dissertation
Degree
Doctor of Philosophy
Department
Chemistry
Advisor's Name
Kathleen S. Rein
Advisor's Title
Committee Chair
Advisor's Name
José Almirall
Advisor's Name
Watson Lees
Advisor's Name
Fenfei Leng
Advisor's Name
David W. Lee
Keywords
Lyngbya, Peptide, Pahayokolide A, Absolute configuration, Biosynthesis, NRPS, Stable isotope incprporation
Date of Defense
11-2009
Abstract
Pahayokolides A-D are cytotoxic cyclic polypeptides produced by the freshwater cyanobacterium Lyngbya sp. strain 15-2 that possess an unusual β-amino acid, 3-amino-2,5,7,8-tetrahydroxy-10-methylundecanoic acid (Athmu). The absolute configuration of pahayokolides A-D was determined using advanced Marfey’s method. It was also confirmed that a pendant N-acetyl-N-methyl leucine moiety in pahayokolide A was absent in pahayokolides B and pahayokolides C-D were conformers of pahayokolide A. Feeding experiments indicated that the biosynthesis of the Athmu sidechain arises from leucine or α-ketoisovalerate, however could not be further extended by three rounds of condensation with malonate units. Putative four peptide and one unique polyketide synthetases in Lyngbya sp. strain 15-2 were identified by using a PCR method and degenerate primers derived from conserved core sequences of known NRPSs and PKSs. Identification of one unique KS domain conflicted with the logic rule that the long side chain of Athmu was assembled by three rounds of ketide extensions if PKSs were involved. A gene cluster (pah) encoding a peptide synthetase putatively producing pahayokolide was cloned, partially sequenced and characterized. Seven modules of the non-ribosomal peptide synthetase (NRPS) were identified. Ten additional opening reading frames (ORFs) were found, responsible for peptide resistance, transport and degradation. Although the predicted substrate specificities of NRPS agreed with the structure of pahayokolide A partially, the disagreement could be explained. However, no PKS gene was found in the pah gene cluster.
Recommended Citation
Liu, Li, "Absolute Configuration and Biosynthesis of Pahayokolide A from Lyngbya sp. Strain 15-2 of the Florida Everglades" (2009). FIU Electronic Theses and Dissertations. Paper 134.
http://digitalcommons.fiu.edu/etd/134