Three-dimensional structure/function analysis of SCP-2-like2 reveals differences among SCP-2 family members

David H Dyer,Vilena Wessely,Katrina T Forest,Que Lan

doi:10.1194/jlr.m700460-jlr200

David H Dyer, Vilena Wessely + Show 2 more

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https://doi.org/10.1194/jlr.m700460-jlr200

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Abstract

Mosquito sterol carrier protein-2 (AeSCP-2) and sterol carrier protein-2-like2 (AeSCP-2L2) are members of the SCP-2 protein family with similar expression profiles in the mosquito life cycle. In an effort to understand how lipids can be transported by different SCP-2 proteins, the three-dimensional crystal structure of AeSCP-2L2 was solved at 1.7 A resolution. AeSCP-2L2 forms a dimer and binds three fatty acids, one of which resides in a position within the internal cavity at a right angle to the others. This first report of ligand-bound dimerized protein in the SCP-2 protein family indicates that the family has a much more divergent mode of interaction with ligands than previously reported. The potential function of AeSCP-2L2 was investigated via in vivo incorporation of [(3)H]cholesterol and [3H]palmitic acid. Overexpression of AeSCP-2L2 in mosquito cells leads to an increased uptake of free fatty acid, whereas knockdown of AeSCP-2L2 in adult females decreases the accumulation of free fatty acid in the fat body from a blood meal. In contrast, overexpression or knockdown of AeSCP-2L2 has no effect on cholesterol uptake. Our results suggest that the main function of AeSCP-2L2 is as a general intracellular fatty acid carrier, as opposed to having a dedicated role in cholesterol transport.

Highlights

Mosquito sterol carrier protein-2 (AeSCP-2) and sterol carrier protein-2-like2 (AeSCP-2L2) are members of the SCP-2 protein family with similar expression profiles in the mosquito life cycle
Overexpression of AeSCP-2L2 did not cause a significant increase of cholesterol uptake (Fig. 4). These results suggest that AeSCP-2L2 is involved in fatty acid uptake in cultured cells
The reported three-dimensional structures of SCP-2 family members in the Protein Data Bank include human SCP-2 (1QND), rabbit SCP-2 (1C44), mosquito SCP-2 (1PZ4), the SCP-2 domain from the human multifunctional enzyme (Mfe) type 2 bound to Triton X-100 (1IKT), and a putative SCP-2 from the hyperthermophilic bacterium Thermus thermophilus [2CX7 (X-ray) and 1WFR (NMR)]

Summary

Introduction

Mosquito sterol carrier protein-2 (AeSCP-2) and sterol carrier protein-2-like (AeSCP-2L2) are members of the SCP-2 protein family with similar expression profiles in the mosquito life cycle. In an effort to understand how lipids can be transported by different SCP-2 proteins, the three-dimensional crystal structure of AeSCP-2L2 was solved at 1.7 Aresolution. Our results suggest that the main function of AeSCP-2L2 is as a general intracellular fatty acid carrier, as opposed to having a dedicated role in cholesterol transport.—Dyer, D. Lan. Three-dimensional structure/function analysis of SCP-2-like reveals differences among SCP-2 family members. Knockdown of SCP-2 in mice results in the disruption of both cholesterol and fatty acid metabolism [14, 15], implying that the vertebrate SCP-2 may be involved in general lipid metabolism. To further our understanding of the function of SCP-2L2, we solved its three-dimensional structure by X-ray crystallography and analyzed the effects of overexpression and underexpression of AeSCP-2 and AeSCP-2L2 on lipid uptake in vivo

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