Structure of factor-inhibiting hypoxia-inducible factor 1: An asparaginyl hydroxylase involved in the hypoxic response pathway

Precise regulation of the evolutionarily conserved hypoxia-inducible transcription factor (HIF) ensures proper adaptation to variations in oxygen availability throughout development and into adulthood. Oxygen-dependent regulation of HIF stability and activity are mediated by hydroxylation of conserved proline and asparagine residues, respectively. Because the relevant prolyl and asparginyl hydroxylases use O₂ to effect these posttranslational modifications, these enzymes are implicated as direct oxygen sensors in the mammalian hypoxic response pathway. Here we present the structure of factor-inhibiting HIF-1 (FIH-1), the pertinent asparaginyl hydroxylase involved in hypoxic signaling. Hydroxylation of the C-terminal transactivation domain (CTAD) of HIF by FIH-1 prevents CTAD association with transcriptional coactivators under normoxic conditions. Consistent with other structurally known hydroxylases, FIH-1 is comprised of a β-strand jellyroll core with both Fe(II) and the cosubstrate 2-oxoglutarate bound in the active site. Details of the molecular contacts at the active site of FIH-1 have been elucidated and provide a platform for future drug design. Furthermore, the structure reveals the presence of a FIH-1 homodimer that forms in solution and is essential for FIH activity.