Allows intracellular utilization of 4-hydroxyproline, one of the major constituents of host collagen, by converting trans-4-hydroxy-L-proline (t4LHyp) to cis-4-hydroxy-D-proline (c4DHyp), which can be further metabolized by intracellular 4-hydroxy-D-proline oxidases. Strong B-cell mitogen. Plays an important role in the regulation of intra- and extracellular amino acid pools, allowing the bacterium to profit from host precursors and enzymatic pathways. Displays no proline racemase activity. trans-4-hydroxy-L-proline = cis-4-hydroxy-D-proline Inhibited by iodoacetate, iodoacetamide and by high amounts (10 mM) of pyrrole-2-carboxylic acid (PYC). Not inhibited by PYC at 1 mM. Homodimer. This enzyme does not require pyridoxal phosphate (PLP) as a cofactor. Belongs to the proline racemase family.