Sterol Carrier Protein X (SCP-x) Regulates Cholesterol Transport in the Migratory Locust Locusta migratoria

Sterol Carrier Protein X (SCP-x) is an evolutionarily conserved lipid transport protein that plays important roles in sterol metabolism. In insects, cholesterol is an essential component of cellular membranes and the precursor of ecdysteroids, yet insects cannot synthesize cholesterol de novo and must obtain it from dietary sources. However, the functional role of SCP-x in cholesterol absorption and transport in insects remains poorly understood. In this study, the SCP-x gene from the migratory locust Locusta migratoria was identified and characterized using transcriptomic data from the midgut and fat body. The full-length LmSCP-x encodes a 404-amino-acid protein containing both the 3-oxoacyl-CoA thiolase domain and the sterol carrier protein-2 domain. Expression analysis revealed that LmSCP-x is predominantly expressed in the midgut and fat body, and subcellular localization experiments showed that the protein is mainly distributed in the cytoplasm. RNA interference-mediated knockdown of LmSCP-x significantly reduced cholesterol levels in the fat body and delayed nymphal development. Structural prediction using AlphaFold 3 further revealed a conserved three-dimensional structure of the SCP-2 domain, and molecular docking identified key amino acid residues involved in cholesterol binding, which were subsequently validated by bio-layer interferometry assays. Together, these results demonstrate that LmSCP-x plays a crucial role in cholesterol transport in L. migratoria and provide new insights into sterol metabolism in insects, offering potential targets for the development of novel pest management strategies.