Structural highlights
FunctionPublication Abstract from PubMedRhamnose methylation of spinosyn critical for insecticidal activity is orchestrated by substrate specificity of three S-adenosyl-L-methionine (SAM) dependent methyltransferases (MTs). Previous in vitro enzymatic assays indicate that 3'-O-MT SpnK accepts the rhamnosylated aglycone (RAGL) and 2'-O-methylated RAGL as substrates, but does not tolerate the presence of a methoxy moiety at the O-4' position of the rhamnose unit. Here we solved the crystal structures of apo and ligand-bound SpnK, and used molecular dynamic (MD) simulations to decipher the molecular basis of substrate specificity. SpnK assembles into a tetramer, with each set of three monomers forming an integrated substrate binding pocket. The MD simulations of SpnK complexed with RAGL or 2'-O-methylated RAGL revealed that the 4'-hydroxyl of the rhamnose unit formed a hydrogen bond with a conserved Asp299 of the catalytic center, which is disrupted in structures of SpnK complexed with 4'-O-methylated RAGL or 2',4'-di-O-methylated RAGL. Comparison with SpnI methylating the C2'-hydroxyl of RAGL reveals a correlation between a DLQT/DLWT motif and the selectivity of rhamnose O-MTs. Together, our structural and computational results revealed the structural basis of substrate specificity of rhamnose O-MTs and would potentially help the engineering of spinosyn derivatives. Structural and computational insights into the regioselectivity of SpnK involved in rhamnose methylation of spinosyn.,Huang S, Ji H, Zheng J Int J Biol Macromol. 2023 Sep 11;253(Pt 3):126763. doi: , 10.1016/j.ijbiomac.2023.126763. PMID:37703985[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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