Department of Microbiology, Immunology, and Molecular Genetics, University of Kentucky, 760 Press Avenue, Lexington, KY 40536, USA.
Department of Host Microbe Interactions, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, TN 38105, USA.
J Struct Biol. 2024 Mar;216(1):108065. doi: 10.1016/j.jsb.2024.108065. Epub 2024 Feb 3.
Bacteria use the fatty acid composition of membrane lipids to maintain homeostasis of the bilayer. β-Ketoacyl-ACP synthase III (FabH) initiates fatty acid biosynthesis and is the primary determinant of the fatty acid composition. FabH condenses malonyl-acyl carrier protein with an acyl-Coenzyme A primer to form β -ketoacyl-acyl carrier protein which is used to make substrates for lipid synthesis. The acyl-Coenzyme A primer determines whether an acyl chain in the membrane has iso, anteiso, or no branching (straight chain) and biophysical properties of the membrane. The soil bacterium Bacillus subtilis encodes two copies of FabH (BsFabHA and BsFabHB), and here we solve their crystal structures. The substrate-free 1.85 Å and 2.40 Å structures of BsFabHA and BsFabHB show both enzymes have similar residues that line the active site but differ in the architecture surrounding the catalytic residues and oxyanion hole. Branching in the BsFabHB active site may better accommodate the structure of an iso-branched acyl-Coenzyme A molecule and thus confer superior utilization to BsFabHA for this primer type. The 2.02 Å structure of BsFabHA•Coenzyme A shows how the active site architecture changes after binding the first substrate. The other notable difference is an amino acid insertion in BsFabHB that extends a cap that covers the dimer interface. The cap topology is diverse across FabH structures and appears to be a distinguishing feature. FabH enzymes have variable sensitivity to natural product inhibitors and the availability of crystal structures help clarify how nature designs antimicrobials that differentially target FabH homologs.
细菌利用膜脂的脂肪酸组成来维持双层的内稳态。β-酮酰-ACP 合酶 III（FabH）起始脂肪酸的生物合成，是脂肪酸组成的主要决定因素。FabH 将丙二酰酰基载体蛋白与酰基辅酶 A 引物缩合形成β-酮酰-酰基载体蛋白，用于合成脂质合成的底物。酰基辅酶 A 引物决定膜中酰基链是否具有异、前异或无支链（直链）以及膜的生物物理性质。土壤细菌枯草芽孢杆菌编码两个 FabH 拷贝（BsFabHA 和 BsFabHB），我们在此解决了它们的晶体结构。无底物的 1.85Å 和 2.40Å 的 BsFabHA 和 BsFabHB 结构表明两种酶都具有相似的残基排列在活性位点，但催化残基和氧阴离子孔周围的结构不同。BsFabHB 活性位点中的支链可能更好地适应异支链酰基辅酶 A 分子的结构，从而使 BsFabHB 对这种引物类型具有更好的利用。BsFabHA•辅酶 A 的 2.02Å 结构显示了在结合第一个底物后活性位点结构如何发生变化。另一个显著的区别是 BsFabHB 中的一个氨基酸插入延伸了覆盖二聚体界面的盖子。盖子拓扑结构在 FabH 结构中多种多样，似乎是一个区别特征。FabH 酶对天然产物抑制剂的敏感性不同，晶体结构的可用性有助于阐明大自然如何设计出针对 FabH 同源物的不同的抗菌药物。
