Leptospira Homoserine O-acetyltransferase Structural Analysis And Catalytic Mechanism, People Coactosin-like Protein Structure Analysis

LiHTA-Homoserine O-acetyltransferase (HTA, EC 2.3.1.31) initiates the methionine biosynthesis pathway by catalyzing the transfer of acetyl group from acetyl-CoA to homoserine. This paper reports the crystal structure of HTA from Leptospira interrogans determined at 2.2 A resolution using the selenomethionyl singlewavelength anomalous diffraction method. HTA is modular and consists of two structurally distinct domains - a core a/β domain containing the catalytic site and a helical bundle called the lid domain. Overall, the structure fold belongs to the a/β hydrolase superfamily with the characteristic 'catalytic triad' residues in the active site. Detailed structure analysis showed the catalytic histidine and serine to be present both in two conformations, which provides a deep insight into the catalytic mechanism for acetyl transfer.hCLP-Human coactosin-like protein is an actin filament binding protein but does not bind to globular actin. It associates with 5-Lipoxygenase both in vivo and in vitro, playing important roles in modulating the activities of actin and 5-Lipoxygenase. Coactosin counteracts the capping activity of capping protein which inhibits the actin polymerization. We determined the crystal structures of human coactosin-like protein by multi-wavelength anomalous dispersion method. The structure showed a high level of similarity to ADF-H domain, although their amino acid sequences share low degree of homology. A few conserved hydrophobic residues that may contribute to the folding were identified. This structure suggests coactosin-like protein bind to F-actin in a different way from ADF/Cofilin family. Combined with the information from previous mutagenesis studies, the binding sites for F-actin and 5-Lipoxygenase were analyzed, respectively. These two sites are quite close, which might prevent F-actin and 5-Lipoxygenase from binding to coactosin simultaneously.