title: Insight into the structural flexibility and function of Mycobacterium tuberculosis isocitrate lyase.
abstract: Isocitrate lyase (ICL), is a key enzyme of the glyoxylate shunt crucial for the survival of Mycobacterium tuberculosis (Mtb) in macrophages during persistent infection. MtbICL catalyses the first step of this carbon anaplerosis cycle and is considered as a potential anti-tubercular drug target. The MtbICL is a tetramer with 222 symmetry, and each subunit of the enzymeis composed of 14 α-helices and 14 β-strands. We studied the conformational flexibility of the enzyme to get a deeper insight into its stability and function. Our studies show that the mutation of His180, close to the MtbICL signature sequence (K193KCGH197) completely abolishes the oligomeric conformation and function of the enzyme. Molecular dynamics studies suggest that the loss of interaction between His180 and Tyr89 most likely alters the orientation of Tyr89 side chain, thereby causing the movement of helices α6, α12, α13 and α14 in the vicinity and affecting the tetrameric assembly. We further show that the oligomerization of MtbICL is primarily mediated by the inter subunit interactions, and strengthened by the helix swapping of α12-α13 between adjacent subunits. Furthermore, the enzyme activity is influenced by the interactions between the residues of lid region (P411NSSTTALTGSTEEGQFH428) and the loop region (T391KHQREV397). Mutation of glutamates of the lid region to non homologous residues (E423A or E424A) or basic residues (E423K or E424K) inactivates the enzyme, whereas the activity is not much compromised in case of homologous mutations (E423D or E424D).
authors.affiliation: Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Sector 10, Jankipuram Extension, Lucknow, PIN 226 031, India.
authors.forename: Harish
authors.initials: H
authors.lastname: Shukla
authors.affiliation: Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Sector 10, Jankipuram Extension, Lucknow, PIN 226 031, India.
authors.forename: Vikash
authors.initials: V
authors.lastname: Kumar
authors.affiliation: Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Sector 10, Jankipuram Extension, Lucknow, PIN 226 031, India.
authors.forename: Amit Kumar
authors.initials: AK
authors.lastname: Singh
authors.affiliation: Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Sector 10, Jankipuram Extension, Lucknow, PIN 226 031, India.
authors.forename: Neha
authors.initials: N
authors.lastname: Singh
authors.affiliation: Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Sector 10, Jankipuram Extension, Lucknow, PIN 226 031, India.
authors.forename: Md
authors.initials: M
authors.lastname: Kashif
authors.affiliation: Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Sector 10, Jankipuram Extension, Lucknow, PIN 226 031, India; Academy of Scientific and Innovative Research, CSIR-Central Drug Research Institute, Sector 10, Jankipuram Extension, Lucknow, PIN 226 031, India.
authors.forename: Mohammad Imran
authors.initials: MI
authors.lastname: Siddiqi
authors.affiliation: Microbiology Division, CSIR-Central Drug Research Institute, Sector 10, Jankipuram Extension, Lucknow, PIN 226 031, India; Academy of Scientific and Innovative Research, CSIR-Central Drug Research Institute, Sector 10, Jankipuram Extension, Lucknow, PIN 226 031, India.
authors.forename: Manju
authors.initials: M
authors.lastname: Yasoda Krishnan
authors.affiliation: Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Sector 10, Jankipuram Extension, Lucknow, PIN 226 031, India; Academy of Scientific and Innovative Research, CSIR-Central Drug Research Institute, Sector 10, Jankipuram Extension, Lucknow, PIN 226 031, India. Electronic address: sohail@cdri.res.in.
authors.forename: Md
authors.initials: M
authors.lastname: Sohail Akhtar
mesh_terms: D000595:Amino Acid Sequence; D055162:Biocatalysis; D004795:Enzyme Stability; D007522:Isocitrate Lyase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D009169:Mycobacterium tuberculosis / Q000201:enzymology*; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D055672:Static Electricity
chemical_list: D007522:Isocitrate Lyase
keywords: Activity; Drug target; Isocitrate lyase; Kinetics; Structure