title: Evaluation of gidB alterations responsible for streptomycin resistance in Mycobacterium tuberculosis.
abstract: OBJECTIVE
  To evaluate gidB alterations for possible impact on the cumulative mechanism underlying the acquisition of high-level streptomycin resistance in Mycobacterium tuberculosis.
  
  
  METHODS
  Fifty-two isolates with high streptomycin resistance and 23 isolates with low streptomycin resistance were sequenced for mutational analysis in the rpsL, rrs and gidB region. As the gidB protein has a complex substrate and no activity assay has yet been formulated, mutants of interest were subjected to in silico modelling and were structurally mapped together with active-site amino acid residues for assessment of the relevance to activity of the mutations found.
  
  
  RESULTS
  Eight novel sense mutations and four novel mis-sense mutations in gidB were identified. Findings showed that active-site morphology is not only greatly affected by mutants lying in close proximity to the active-site pocket, but also by other mutations altering secondary-structure motifs and having an overall effect on protein structure.
  
  
  CONCLUSIONS
  We conclude that gidB mutations address many unanswered questions and explain the whole story behind phenotypic streptomycin-resistant strains exhibiting no mutation in rpsL or rrs. They also validate the hypothesis of sequential progression of resistance from low to high due to the existence of gidB alterations in the genetic background.
authors: Department of Orthopaedics, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi 110029, India jitu_jitender1@rediffmail.com.
authors: Jitender S
authors: JS
authors: Verma
authors: National JALMA Institute for Leprosy and Other Mycobacterial Diseases (ICMR), Tajganj, Agra 282001, India.
authors: Yash
authors: Y
authors: Gupta
authors: Department of Microbiology, Vardhman Mahavir Medical College and Safdarjung Hospital, New Delhi 110029, India.
authors: Deepthi
authors: D
authors: Nair
authors: Department of Bio-Sciences, Jamia Millia Islamia, New Delhi 110025, India.
authors: Nikhat
authors: N
authors: Manzoor
authors: National Centre for Disease Control, Sham Nath Marg, New Delhi 110054, India.
authors: Rajinder S
authors: RS
authors: Rautela
authors: National Centre for Disease Control, Sham Nath Marg, New Delhi 110054, India.
authors: Arvind
authors: A
authors: Rai
authors: Director General, Indian Council of Medical Research and Secretary, Department of Health Research, Ministry of Health and Family Welfare, India.
authors: Vishwa M
authors: VM
authors: Katoch
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics*; D024881:Drug Resistance, Bacterial / Q000187:drug effects / Q000235:genetics*; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D009154:Mutation / Q000235:genetics; D009169:Mycobacterium tuberculosis / Q000187:drug effects / Q000235:genetics*; D017433:Protein Structure, Secondary; D013307:Streptomycin / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D013307:Streptomycin
keywords: DNA sequencing; drug resistance; in silico modelling; novel mutations