Download MendeleyStructural characterization and functional analysis of cystathionine beta-synthase: an enzyme involved in the reverse transsulfuration pathway of Bacillus anthracis.
Devi, S., Abdul Rehman, S.A., Tarique, K.F., Gourinath, S.(2017) FEBS J 284: 3862-3880
- PubMed: 28921884
- DOI: https://doi.org/10.1111/febs.14273
- Primary Citation of Related Structures:
5XW3 - PubMed Abstract:
The reverse transsulfuration pathway has been reported to produce cysteine from homocysteine in eukaryotes ranging from protozoans to mammals while bacteria and plants produce cysteine via a de novo pathway. Interestingly, the bacterium Bacillus anthracis includes enzymes of the reverse transsulfuration pathway viz. cystathionine β-synthase [BaCBS, previously annotated to be an O-acetylserine sulfhydrylase (OASS)] and cystathionine γ-lyase. Here, we report the structure of BaCBS at a resolution of 2.2 Å. The enzyme was found to show CBS activity only with activated serine (O-acetylserine) and not with serine, and was also observed to display OASS activity but not serine sulfhydrylase activity. BaCBS was also found to produce hydrogen sulfide (H 2 S) upon reaction of cysteine and homocysteine. A mutational study revealed Glu 220, conserved in CBS, to be necessary for generating H 2 S. Structurally, BaCBS display a considerably more open active site than has been found for any other CBS or OASS, which was attributed to the presence of a helix at the junction of the C- and N-terminal domains. The root-mean-square deviation (RMSD) between the backbone Cα carbon atoms of BaCBS and those of other CBSs and OASSs were calculated to be greater than 3.0 Å. The pyridoxal 5'-phosphate at the active site was not traced, and appeared to be highly flexible due to the active site being wide open. Phylogenetic analysis revealed the presence of an O-acetylserine-dependent CBS in the bacterial domain and making separate clade from CBS and OASS indicating its evolution for specific function.
Organizational Affiliation:
Structural Biology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi, India.
