Solution Nuclear Magnetic Resonance Studies of Sterol Carrier Protein 2 Like 2 (SCP2L2) Reveal the Insecticide Specific Structural Characteristics of SCP2 Proteins in <i>Aedes aegypti</i> Mosquitoes

Sterol carrier protein 2 like 2 from <i>Aedes aegypti</i> (<i>Ae</i>SCP2L2) plays an important role in lipid transport in mosquitoes for its routine metabolic processes. Repeated unsuccessful attempts to crystallize ligand free SCP2L2 prompted us to undertake nuclear magnetic resonance (NMR) spectroscopy to determine its three-dimensional structure. We report here the three-dimensional structures and dynamics of apo-<i>Ae</i>SCP2L2 and its complex with palmitate. The ¹⁵N heteronuclear single-quantum coherence spectrum of apo-<i>Ae</i>SCP2L2 displayed multiple peaks for some of the amide resonances, implying the presence of multiple conformations in solution, which are transformed to a single conformation upon formation of the complex with plamitate. The three-dimensional structures of apo-<i>Ae</i>SCP2L2 and palmitated <i>Ae</i>SCP2L2 reveal an α/β mixed fold, with five β-strands and four α-helices, very similar to the other SCP2 protein structures. Unlike the crystal structure of palmitated <i>Ae</i>SCP2L2, both solution structures are monomeric. It is further confirmed by the rotational correlation times determined by NMR relaxation times (<i>T</i>₁ and <i>T</i>₂) of the amide protons. In addition, the palmitated <i>Ae</i>SCP2L2 structure contains two palmitate ligands, bound in the binding pocket, unlike the three palmitates bound in the dimeric form of <i>Ae</i>SCP2L2 in the crystals. The relaxation experiments revealed that complex formation significantly reduces the dynamics of the protein in solution