OXIDOREDUCTASE, PROLINE UTILIZATION A, PUTA, FLAVOENZYME, DNA-BINDING, FAD, FLAVOPROTEIN, MULTIFUNCTIONAL ENZYME, NAD, PROLINE METABOLISM, REPRESSOR, TRANSCRIPTION, TRANSCRIPTION REGULATION CRYSTAL STRUCTURE REDUCED PUTA86-630 MUTANT Y540S COMPLEXED WITH L-PROLINE 3E2S