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 S.novella to grow on t4LHyp as a sole carbon source. trans-4-hydroxy-L-proline = cis-4-hydroxy-D-proline Belongs to the proline racemase family.