Abstract
The cyanotoxin microcystin (MC) is a secondary metabolite, synthesized by nonribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) enzymes. It has many isoforms and the mechanism of its diversity is not well understood. One of the MC synthetase genes, mcyA, codes for the McyA module containing two adenylation (A) domains. The first domain, McyA-A1, generally binds to L-serine (L-ser). Then the N-methyl transferase (NMT) domain converts L-Ser into N-methyldehydroalanine (Mdha), which usually occupies position 7 on the MC molecule. However, various other amino acids (AAs) might also be present at this position. In this study, bioinformatic analyses of selected cyanobacteria were performed to understand whether genetic information in the first adenylation domain of mcyA could explain incorporation of different AAs at position 7 of the MC molecule. Binding pocket signatures of McyA-A1 and putative activated AAs were determined via various bioinformatics tools. Maximum likelihood phylogenetic trees of full length mcyA, mcyA-A1 and 16S rRNA genes were prepared in Mega 6. Phylogenetic analysis of mcyA-A1 nucleotide sequences was in agreement with the predictions of activated AAs by McyA-A1. In comparison with the 16S rRNA and full length mcyA gene trees, mcyA-A1 phylogenetic trees suggested horizontal transfer of the A domain in either Planktothrix agardhii (Gomont) Anagnostidis & Komárek or Planktothrix rubescens (De Candolle ex Gomont) Anagnostidis & Komárek strains. Predictions of activated AAs were generally in agreement with the chemically determined position 7 AAs. However, there were exceptions suggesting the multispecificity of the first A domain of McyA in some cyanobacteria.
Highlights
There are approximately 500 natural amino acids [1] and they can be classified based on their R groups, stereoisomer structures (D- and L-form), being proteinogenic or nonproteinogenic
Bioinformatic analyses of selected cyanobacteria were performed to understand whether genetic information in the first adenylation domain of mcyA could explain incorporation of different amino acids (AAs) at position 7 of the MC molecule
Binding pocket analyses for McyA-A1 sequences were performed to predict which AA was incorporated at position 7 of the MC molecule
Summary
There are approximately 500 natural amino acids [1] and they can be classified based on their R groups, stereoisomer structures (D- and L-form), being proteinogenic or nonproteinogenic. Proteinogenic amino acids are all 20 kinds of L-form amino acids, where mRNA, tRNA and ribosomes are involved in the protein synthesis pathway. Nonproteinogenic amino acids are D-form or β-amino acids and synthesized by either non-ribosomal peptide. Engineering and Natural Sciences, Bursa Technical University, Bursa, Turkey. Sec. Metabolite, Vol 7, No 4, (2020) pp. 275-285 synthetases (NRPSs), polyketide synthases (PKSs) or hybrid NRPS/PKS modular enzyme systems Metabolite, Vol 7, No 4, (2020) pp. 275-285 synthetases (NRPSs), polyketide synthases (PKSs) or hybrid NRPS/PKS modular enzyme systems
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