Proly] 4-hydroxylase (P4H) catalyzes the post-translational hydroxylation of proline residues in collagen strands. The enzyme is an alpha(2)beta(2) tetramer in which the alpha subunits contain the catalytic active sites and the beta subunits (protein disulfide isomerase) maintain the a subunits in a soluble and active conformation. Heterologous production of the native alpha(2)beta(2) tetramer is challenging and had not been reported previously in a prokaryotic system. Here, we describe the production of active human P4H tetramer in Eseherichia coli from a single bicistronic vector. P4H production requires the relatively oxidizing cytosol of Origami B(DE3) cells. Induction of the wild-type alpha(l) cDNA in these cells leads to the production of a truncated alpha subunit (residues 235-534), which assembles with the beta subunit. This truncated P4H is an active enzyme, but has a high K-m, value for long substrates. Replacing the Met235 codon with one for leucine removes an alternative start codon and enables production of full-length alpha subunit and assembly of the native alpha(2)beta(2), tetramer in E. coli cells to yield 2 mg of purified P4H per liter of culture (0.2 mg/g of cell paste). We also report a direct, automated assay of proline hydroxylation using high-performance liquid chromatography. We anticipate that these advances will facilitate structure-function analyses of P4H. (C) 2004 Elsevier Inc. All rights reserved.