Investigation of The Dimer Interface and Active Site in Pyridoxal 5' Phosphate Enzymes Cystathionine B- Lyase and Cystathionine y- Lyase

Cystathionine β-lyase (CBL) catalyses the PLP-dependent β-elimination of cystathionine, yielding homocysteine, pyruvate and ammonia, while the γ-elimination of this pseudosymmetric substrate by cystathionine γ-lyase (CGL) produces cysteine, α-ketobutyrate and ammonia. The β versus γ-elimination reaction specificity of the structurally conserved eCBL and yCGL enzymes provides an ideal system to probe the factors that regulate activity and specificity. These studies will enable the continued development of our understanding of the mechanisms whereby PLP-dependent enzymes regulate substrate and reaction specificity, building a framework that will facilitate future studies aiming to engineer these enzymes for use in various industrial processes as well as for the development of novel antimicrobials and therapeutics. Comparison of the structures of Escherichia coli CBL (eCBL) and Saccharomyces cerevisiae CGL identified differences at the dimer interface and within the active site and their impact on enzyme activity is explored in chapters 2 and 3 of this thesis, respectively.