Glycine radical enzyme that catalyzes the dehydration of the non-proteinogenic amino acid trans-4-hydroxy-L-proline (Hyp) to produce delta(1)-pyrroline-5-carboxylate (P5C). Is involved in the anaerobic degradation of 4-hydroxyproline. trans-4-hydroxy-L-proline = (S)-1-pyrroline-5-carboxylate + H(+) + H2O kcat is 45 sec(-1) for trans-4-hydroxy-L-proline as substrate. Requires the activating protein PflE to generate the key active site glycyl radical on Gly-765 that is involved in catalysis. Belongs to the glycyl radical enzyme (GRE) family. HYPD subfamily.