Catalyzes the epimerization of trans-4-hydroxy-L-proline (t4LHyp) to cis-4-hydroxy-D-proline (c4DHyp). May be involved in a degradation pathway of t4LHyp, which would allow A.tumefaciens to grow on t4LHyp as a sole carbon source. Can also catalyze the epimerization of trans-3-hydroxy-L-proline (t3LHyp) to cis-3-hydroxy-D-proline (c3DHyp) in vitro. Displays no proline racemase activity. trans-4-hydroxy-L-proline = cis-4-hydroxy-D-proline kcat is 0.86 sec(-1) for t4LHyp epimerization. kcat is 4.0 sec(-1) for t3LHyp epimerization. Is up-regulated when the bacterium is grown on t4LHyp or t3LHyp as sole carbon source. Belongs to the proline racemase family.