Structural Insight into the Tetramerization of an Iterative Ketoreductase SiaM through Aromatic Residues in the Interfaces

Abstract

In the biosynthesis of polyketides, ketoreductases (KRs) are an important group of enzymes that determine the chiralities of the carbon backbones. SiaM is a special member of this group that can recognize substrates with different lengths and can be used iteratively. Here we report the crystal structure of SiaM. Structural analysis indicates that the overall structure resembles those of other KRs. However, significant disparity can be found in the conserved LDD motif that is replaced with IRD motif in SiaM. The isoleucine and aspartic acid residues take similar orientations as leucine and aspartic acid in the conserved LDD motif, while the arginine residue points out towards the solvent. PISA analysis shows that SiaM forms a tetramer. Several aromatic residues are found in the interfaces, which have aromatic stacking interactions with the aromatic residues in the neighboring protomers. Mutagenesis studies performed on the aromatic residues show that these sites are important for maintaining the structural integrity of SiaM. However, the aromatic residues contribute differently to the enzymatic activity. In the N-terminal interface, the aromatic residues can be replaced with leucine without affecting the enzymatic activity while, in the other interface, such mutations abolish the enzymatic activity.

The Uncommon Enzymology of Cis-Acyltransferase Assembly Lines

“…215 AntM is highly homologous to SiaM, the trans-KR that reduces β -keto groups of acyl chains bound to the SIA7248 trans-AT assembly line and whose structure is known (PDB 3WOH). 216,217…”

“…215 AntM is highly homologous to SiaM, the trans-KR that reduces β-keto groups of acyl chains bound to the SIA7248 trans-AT assembly line and whose structure is known (PDB 3WOH). 216,217 A trans-KR may also be operating in thuggacin (Chondromyces crocatus) module 2. 130 Thuggacin (C. crocatus) module 2 is thought to generate an α/β-trans double bond, like thuggacin (S. cellulosum) module 2.…”

Crystal structures of FolM alternative dihydrofolate reductase 1 from Brucella suis and Brucella canis

“…of $1.5 A ˚. These protozoan pteridine reductases are more similar to BsFolM and BcFolM than to the structures from Bacillus anthracis (Zaccai et al, 2008), Streptomyces (Wang et al, 2014), Serratia marcescens (Liu et al, 2018), Thermus thermophilus (Asada et al, 2009) or other bacteria.…”

Ketide Synthase (KS) Domain Prediction and Analysis of Iterative Type II PKS Gene in Marine Sponge-Associated Actinobacteria Producing Biosurfactants and Antimicrobial Agents

“…The mixed clustering of different sponge associated KS domains already been documented here for the first time we are reporting the evolutionary relatedness of KS domains of type II PKS and ketosynthase from D. nigra and F. cavernosa isolates. According to recent literatures, the PKS genes and their products exhibit novel insights in antimicrobial drug discovery ( Selvin, 2009 ; Sasso et al, 2014 ; Wang et al, 2014 ). KS domain of type II PKS phylogeny is also highly need to know their relationship and structural diversity.…”