Journal of Biochemistry Advance Access published online on May 15, 2008
Journal of Biochemistry, doi:10.1093/jb/mvn067
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© 2008 The Japanese Biochemical Society
Characterization of Pyridoxal 5'-Phosphate Binding Domain and Folding Intermediate of Bacillus subtilis Serine Hydroxymethyltransferase: An Autonomous Folding Domain
1Division of Biocybernetics, Institute of Nuclear Medicine and Allied Sciences, Delhi 110 054, India
2Division of Molecular and Structural Biology, Central Drug Research Institute, Lucknow 226 001, India.
*To whom correspondence should be addressed: Dr. Anant Narayan Bhatt: Division of Biocybernetics, Institute of Nuclear Medicine and Allied Sciences, Delhi 110 054, India. Tel: 00-91-011-2390 5130, FAX : 00-91-011-2391 9509, E-mail : anant.bhatt{at}indiatimes.com
Received March 5, 2008; Accepted April 27, 2008
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Summary
The pyridoxal-5'-phosphate-binding domain (PLPbd) of bsSHMT (Bacillus subtilis serine hydroxymethyltransferase) was cloned and overexpressed in Escherichia coli. The recombinant protein was solublized, refolded and purified from inclusion bodies by rapid mixing followed by ion exchange chromatography. Structural and functional studies suggested the native form of the domain which obtained as a monomer and had similar secondary and tertiary structural properties as when present in the bsSHMT. The domain also binds to the PLP however with slight lesser affinity than the native enzyme. GdmCl (guanidium chloride)-induced equilibrium unfolding of the recombinant PLP binding domain showed a single monophasic transition which corresponds with the second phase transition of the GdmCl-induced unfolding of bsSHMT. The results indicate that PLPbd of bsSHMT is an independent domain, which attains its tertiary structure before the dimerization of partially folded monomer and behaves as a single cooperative unfolding unit under equilibrium conditions.
Key Words: Autonomous folding domain, Conserved domain, PLP-binding domain, Refolding and Serine hydroxymethyltransferase