Expression and characterization of alpha-(1,4)-glucan branching enzyme Rv1326c of Mycobacterium tuberculosis H37Rv.

Garg, Saurabh K and Alam, Md Suhail and Kishan, K V Radha and Agrawal, Pushpa (2007) Expression and characterization of alpha-(1,4)-glucan branching enzyme Rv1326c of Mycobacterium tuberculosis H37Rv. Protein expression and purification, 51 (2). pp. 198-208. ISSN 1046-5928

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Glycogen branching enzyme (GlgB, EC catalyzes the third step of glycogen biosynthesis by the cleavage of an alpha-(1,4)-glucosidic linkage and subsequent transfer of cleaved oligosaccharide to form a new alpha-(1,6)-branch. A single glgB gene Rv1326c is present in Mycobacterium tuberculosis. The predicted amino acid sequence of GlgB of M. tuberculosis has all the conserved regions of alpha-amylase family proteins. The overall amino acid identity to other GlgBs ranges from 48.5 to 99%. The glgB gene of M. tuberculosis was cloned and expressed in Escherichia coli. The recombinant protein was purified to homogeneity using metal affinity and ion exchange chromatography. The recombinant protein is a monomer as evidenced by gel filtration chromatography, is active as an enzyme, and uses amylose as the substrate. Enzyme activity was optimal at pH 7.0, 30 degrees C and divalent cations such as Zn2+ and Cu2+ inhibited activity. CD spectroscopy, proteolytic cleavage and mass spectroscopy analyses revealed that cysteine residues of GlgB form structural disulfide bond(s), which allow the protein to exist in two different redox-dependent conformational states. These conformations have different surface hydrophobicities as evidenced by ANS-fluorescence of oxidized and reduced GlgB. Although the conformational change did not affect the branching enzyme activity, the change in surface hydrophobicity could influence the interaction or dissociation of different cellular proteins with GlgB in response to different physiological states.

Item Type: Article
Additional Information: Copyright of this article belongs to Elsevier Science.
Uncontrolled Keywords: Mycobacterium tuberculosis; glgB; Glucan branching enzyme; Trypsin cleavage; ANS fluorescence; Redox-dependent protein conformation; Disulfide bond
Subjects: Q Science > QR Microbiology
Depositing User: Dr. K.P.S.Sengar
Date Deposited: 09 Jan 2012 04:21
Last Modified: 09 Jan 2012 04:21

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