Function analysis of cystathionine gamma-lyase mutants

Jindřich Hašek

Institute of Macromolecular Chemistry, Academy of Sciences of the Czech Republic,

Heyrovského nám. 2, Praha 6, <cny>Czech Republic

Cystathionine gamma-lyase (EC 4.4.1.1) abbreviated as CTH is a regulatory and metabolic enzyme with pyridoxal phosphate (PLP, vitamin B6) as a co-factor. It cleaves cystathionine (2-amino-4-(2-amino-2-carboxy-ethyl) thio-butanoic acid) into cysteine, ammonia and α-ketobutyrate. It produces also hydrogen sulfide (H₂S) putatively active in cell proliferation and neurotransmission. Deficiency in CTH function is associated with cystathioninuria often considered as a cause of severe psychomotorical or mental retardation, strabism or epilepsy. CTH deficiency is considered to be a common biochemical phenotype in the population of Central European ancestry (estimated frequency 1:3000).

Crystallographic analysis of human hCTH (4x403 residue complexes of apo-hCTH, hCTH-PLP and hCTH-PLP-PAG [1]) explains why its correct function is restricted to its tetrameric complexes only and why four catalytic sites of the tetramer are not equivalent. It also shows a way of substrate path through a deep catalytic cavity and large conformational changes (flaps opening) during PLP binding.

The analysis of structure effects of 8 genetically related mutations for which the physiological and clinical data are available on a sample of homozygote and heterozygote patients (Arg62His, Thr67Ile, Thr311Ile, Arg197Cys, Gln240Glu, Thr311Ile, Ser403Ile, deletion Gly57–Gln196) showed clear correlation between the mutations and the observed plasma concentrations of metabolites [2]. A positive effect of the vitamin B6 administration for some mutations and zero responsiveness for other mutations is also evident from the molecular structure. However, frequent barriers or by-passes of processes in human body explain why the genotype-phenotype correlation, i.e. the expression of genotype into the actual patients health and mental state is not deterministic and has many exceptions.

1. Sun Q, Collins R, Huang S, Holmberg-Schiavone L, Anand GS, Tan C-H, van-den-Berg S, Deng L-W, Moore PK, Karlberg T, and Sivaraman J, Structural basis for the inhibition mechanism of human cystathionine-γ-lyase: an enzyme responsible for the production of H2S. J.Biol.Chem. (2009); doi:10.1074/jbc.M805459200

2. Mudd S.H., Kraus J.P., Hašek J., Kožich V., Collard R., Vanezia S., Janošíková B., Wang J., Stabler S.P., Allen R.H., Cornelis J., Finn C.T., Chien Y-H., Hwu W-L. and Hegele R.A. Cystathionine γ-lyase: clinical, metabolic, genetic, and structural studies. Molecular Genetics and Metabolism (2009) (in press).

The work was supported by the Czech Science Foundation (project 305/07/1073)