title: Thermal, chemical and pH induced denaturation of a multimeric β-galactosidase reveals multiple unfolding pathways.
abstract: BACKGROUND
  In this case study, we analysed the properties of unfolded states and pathways leading to complete denaturation of a multimeric chick pea β-galactosidase (CpGAL), as obtained from treatment with guanidium hydrochloride, urea, elevated temperature and extreme pH.
  
  
  RESULTS
  CpGAL, a heterodimeric protein with native molecular mass of 85 kDa, belongs to α+β class of protein. The conformational stability and thermodynamic parameters of CpGAL unfolding in different states were estimated and interpreted using circular dichroism and fluorescence spectroscopic measurements. The enzyme was found to be structurally and functionally stable in the entire pH range and upto 50 °C temperature. Further increase in temperature induces unfolding followed by aggregation. Chemical induced denaturation was found to be cooperative and transitions were irreversible, non-coincidental and sigmoidal. Free energy of protein unfolding (ΔG(0)) and unfolding constant (K(obs)) were also calculated for chemically denatured CpGAL.
  
  
  CONCLUSIONS
  The protein seems to use different pathways for unfolding in different environments and is a classical example of how the environment dictates the path a protein might take to fold while its amino acid sequence only defines its final three-dimensional conformation. The knowledge accumulated could be of immense biotechnological significance as well.
authors.affiliation: School of Biotechnology, Faculty of Science, Banaras Hindu University, Varanasi, India.
authors.forename: Devesh
authors.initials: D
authors.lastname: Kishore
authors.forename: Suman
authors.initials: S
authors.lastname: Kundu
authors.forename: Arvind M
authors.initials: AM
authors.lastname: Kayastha
mesh_terms: D029863:Cicer / Q000737:chemistry* / Q000201:enzymology; D002942:Circular Dichroism; D019791:Guanidine / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D010940:Plant Proteins / Q000737:chemistry* / Q000302:isolation & purification; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D055503:Protein Multimerization; D055550:Protein Stability; D058767:Protein Unfolding; D013050:Spectrometry, Fluorescence; D013696:Temperature; D013816:Thermodynamics; D014508:Urea / Q000737:chemistry; D001616:beta-Galactosidase / Q000737:chemistry* / Q000302:isolation & purification
chemical_list: D010940:Plant Proteins; D014508:Urea; D001616:beta-Galactosidase; D019791:Guanidine