Prolyl 4-hydroxylases (P4Hs) are members of the Fe(2+ )and 2-oxoglutarate- dependent oxygenases family, which play central roles in the collagen stabilization, hypoxia sensing, and translational regulation in eukaryotes. Thus far, nothing is known about the role of P4Hs in development and pathogenesis in oomycetes. Here we show that the Phytophthora capsici genome contains five putative prolyl 4-hydroxylases. In mycelia, all P4Hs were downregulated in response to hypoxia, but the expression of PcP4H1 was most affected. Strikingly, Pc4H1 was upregulated more than 110 fold at the onset of infection, and Pc4H5 was upregulated seven fold, while the expression of other P4H's were unchanged. Similar to well-characterized P4H proteins, the crystallographic structure of PcP4H1 contains a highly conserved double-stranded beta-helix core fold and catalytic residues. However, the binding affinity of 2-oxoglutarate to PcP4H1 is very low. The extended C-terminal alpha-helix bundle and longer beta 2-beta 3 disordered substrate binding loop may help in confirming the peptide target of this enzyme. (C) 2018 Elsevier Inc. All rights reserved.