Allows intracellular utilization of 4-hydroxyproline, one of the major constituents of host collagen, by converting 4-hydroxy-L-proline to 4-hydroxy-D-proline, 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. 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.