Crystal structures of open and closed forms of d‐serine deaminase from Salmonella typhimurium – implications on substrate specificity and catalysis

摘要: Metabolism of D-amino acids is considerable interest due to their key importance in cell structure and function. Salmonella typhimurium D-serine deaminase (StDSD) a pyridoxal 5' phosphate (PLP) dependent enzyme that catalyses degradation D-Ser pyruvate ammonia. The first crystal described here reveals typical Foldtype II or tryptophan synthase beta subunit fold PLP-dependent enzymes. Although holoenzyme was used for crystallization both wild-type StDSD (WtDSD) selenomethionine labelled (SeMetDSD), significant electron density not observed the cofactor, indicating has low affinity cofactor under conditions. Interestingly, unexpected conformational differences were between two structures. WtDSD an open conformation while SeMetDSD, crystallized presence isoserine, closed suggesting likely undergo changes upon binding substrate as other Electron corresponding plausible sodium ion found near active site but state enzyme. Examination modelling suggests Thr166 may be involved abstraction proton from C alpha atom substrate. Apart physiological reaction, a, b elimination D-Thr, D-Allothr L-Ser alpha-keto provides molecular framework necessary understanding rate reaction with these substrates.