Structural basis for targeting human cancer antigen STEAP1 with antibodies

Wout Oosterheert, Piet Gros
2020 · doi:10.1101/2020.03.07.981829
preprint OA: closed CC-BY-NC-ND-4.0
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Abstract

Six-transmembrane epithelial antigen of the prostate (STEAP1) is an integral membrane protein that is highly upregulated on the cell surface of several human cancers, making it a promising therapeutic target. It shares sequence homology with three enzymes (STEAP2-4) that catalyze the NADPH-dependent reduction of iron(III). However, STEAP1 lacks an intracellular NADPH-binding domain and does not exhibit cellular ferric-reductase activity. Thus, both the molecular function of STEAP1 and its role in cancer progression remain elusive. Here, we present a ~3.0 Å cryo-electron microscopy structure of trimeric human STEAP1 bound to three Fab-fragments of the clinically employed antibody mAb120.545. STEAP1 adopts a reductase-like conformation and interacts with the Fabs through its extracellular helices. Enzymatic assays in human cells reveal that STEAP1 promotes iron(III) reduction when fused to the intracellular NADPH-binding domain of its family member STEAP4, implicating STEAP1 as a functional ferric reductase in STEAP hetero-trimers. Our work provides a foundation for deciphering the molecular mechanisms of STEAP1 and will be instrumental in the design of new therapeutic strategies to target STEAP1 in cancer.

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License: CC-BY-NC-ND-4.0