Structural basis of the specificity of amidinohydrolases involved in the final steps of the biosyntheses of large linear and cyclic polyketides Marcio DIAS 1,2 , Hui Hong 3,4 , Jademilson Celestino dos Santos 1 , Tabata Peres Cardoso 1,5 , Gabriel S. de Oliveira 1 , Peter Leadlay 3 1 Institute of Biomedical Science/University of Sao Paulo, Brazil, 2 University of Warwick, UK, 3 University of Cambridge, UK, 4 Isomerase Therapeutics Ltd, Cambridge, UK, 5 University of State of Sao Paulo, Brazil During the biosynthesis of a number of marginolactones such as desertomycin A or giant polyenes such as clethramycin and mediomycins, an amidinohydrolase plays an important role in deprotecting a 4-guanidinobutyrate from the starter unit of the polyketide synthase and consequently remove the amidino group. This strategy seems to be adopted to avoid the cyclization or its early event in the biosynthesis of these natural products. Since desertomycin and mediomycin are cyclic and linear polyketides, respectively, the amidinohydrolases involved in these final maturation steps should have specialties do recognize quite different substrates. In vitro studies, also confirms that these enzymes can not be swapped in their biosynthesis. In order to understand how the amidinohydrolases involved in the biosynthesis of desertomycin A and mediomycin maturation can specifically catalyze their reactions in a cyclic and a linear polyketide, respectively, we solved the structure of these enzymes using protein crystallography. As expected the crystal structures for these enzymes indicate that they conserve the fold, which is similar to other amidinohydrolases, which is constituted of a homohexameric quaternary structure and the coordination of key magnesium or manganese in the active site, which is essential for the catalysis. Interestingly, in the analysis of the sequence alignment, we can observe that these two amidinohydrolases herein studied has a more distinct difference in the N-terminal region. The amidinohydrolase involved in the biosynthesis of linear polyketide has a longer N-terminal sequence in contrast to the cyclic one. By the analysis of the structure of these two enzymes, we can observe that the N-terminal region protrudes into the adjacent protomer of the hexamer decreasing the volume of the regions near the active site and consequently it should play a role in the specificity of its substrate. Structurally this N-terminal loop limits the size of the active site, which is in agreement with the necessity of a narrow cavity for linear polyketides in contrast to a larger active site for cyclic ones. In this study, we showed so far, the different strategies that nature uses to discriminate different substrates involved in the deprotecting group involved in the last steps of giant polyketides. Funding: FAPESP
P14
© The Author(s), 2022
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