NMR structure and function of Helicoverpa armigera sterol carrier protein-2, an important insecticidal target from the cotton bollworm

Abstract

The cotton bollworm, Helicoverpa armigera, has developed strong resistance to many insecticides. Sterol Carrier Protein-2 (SCP-2) is an important non-specific lipid transfer protein in insects and appears to be a potential new target. In order to elucidate the structure and function of Helicoverpa armigera SCP-2 (HaSCP-2), NMR spectroscopy, docking simulations, mutagenesis and bioassays were performed. HaSCP-2 composed of five α-helices and four stranded β-sheets. The folds of α-helices and β-sheets interacted together to form a hydrophobic cavity with putative entrance and exit openings, which served as a tunnel for accommodating and transporting of lipids. Several sterols and fatty acids could interact with HaSCP-2 via important hydrophobic sites, which could be potential targets for insecticides. Mutagenesis experiments indicated Y51, F53, F89, F110, I117 and Q131 may be the key functional sites. HaSCP-2 showed high cholesterol binding activity and SCP-2 inhibitors (SCPIs) could inhibit the biological activity of HaSCP-2. SCPI-treated larvae at young stage showed a significant decrease of cholesterol uptake in vivo. Our study describes for the first time a NMR structure of SCP-2 in lepidopteran H. armigera and reveals its important function in cholesterol uptake, which facilitates the screening of effective insecticides targeting the insect cholesterol metabolism.

NPC1b as a novel target in controlling the cotton bollworm, Helicoverpa armigera

“…However, unlike mammals, insects and other arthropods cannot synthesize sterols de novo , and thus typically obtain them from food. Previous studies have demonstrated that interfering with dietary cholesterol usage delays insect growth and increases insect mortality …”

“…This absorbing process includes two steps: (i) dietary cholesterol transportation through the apical membrane of enterocytes into cells, and (ii) intracellular cholesterol trafficking through the cytoplasm to the basal membrane where cholesterol is loaded into lipophorin . Sterol carrier protein‐2 (SCP‐2), a soluble protein abundant in enterocyte cytoplasm, has been shown to play an important role in the second step . Inhibitors targeting SCP‐2 significantly restricted dietary cholesterol trafficking, and showed high toxicity to insect pests and low toxicity to mammals that can synthesize their own cholesterol .…”

Biological evaluation of a series of benzothiazole derivatives as mosquitocidal agents

“…Moreover, single SCP-2 domain genes have also been proven to be expanded in mosquitoes [13]. Cholesterol is crucial for insects in order to grow, develop and reproduce, but they are not capable of synthesizing cholesterol de novo [14,15]. The mosquito SCP-2, Ae.…”

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

“…More recently, in vivo as well as in silico experiments have shown thiosemicarbazones as larvicides of A. aegypti . The structure and functional studies of other SCP2 proteins have also shown the insecticide specific affinity by several other small molecules. , …”

“…10 The structure and functional studies of other SCP2 proteins have also shown the insecticide specific affinity by several other small molecules. 16,17 A. aegypti sterol carrier protein 2 (AeSCP2) and its isoforms are ∼13 kDa proteins, which share <35% sequence similarity among them and <15% with those of vertebrates. 6,18−21 The structural differences between the vertebrate and mosquito SCP2 revealed the absence of a short helical fragment between α-helix 1 and β-strand 1, suggesting its role in the insecticide specificity in mosquitoes.…”