Molecular cloning, overexpression, and characterization of autophosphorylation in calcium-dependent protein kinase 1 (CDPK1) from Cicer arietinum

In plants, calcium-dependent protein kinases (CDPKs) are key intermediates in calcium-mediated signaling that couple changes in Ca2+ levels to a specific response. In the present study, we report the high-level soluble expression of calcium-dependent protein kinase1 from Cicer arietinum (CaCDPK1) in Escherichia coli. The expression of soluble CaCDPK1 was temperature dependent with a yield of 3-4 mg/l of bacterial culture. CaCDPK1 expressed as histidine-tag fusion protein was purified using Ni-NTA affinity chromatography till homogeneity. The recombinant CaCDPK1 protein exhibited both calcium-dependent autophosphorylation and substrate phosphorylation activities with a V (max) and K (m) value of 13.2 nmol/min/mg and 34.3 mu M, respectively, for histone III-S as substrate. Maximum autophosphorylation was seen only in the presence of calcium. Optimum temperature for autophosphorylation was found to be 37 A degrees C. The recombinant protein showed optimum pH range of 6-9. The role of autophosphorylation in substrate phosphorylation was investigated using histone III-S as exogenous substrate. Our results show that autophosphorylation happens before substrate phosphorylation and it happens via intra-molecular mechanism as the activity linearly depends on enzyme concentrations. Autophosphorylation enhances the kinase activity and reduces the lag phase of activation, and CaCDPK1 can utilize both ATP and GTP as phosphodonor but ATP is preferred than GTP.

Cloning, expression, purification, crystallization and preliminary X-ray studies of argininosuccinate lyase (Rv1659) from Mycobacterium tuberculosis

The last enzyme in the arginine-biosynthesis pathway, argininosuccinate lyase, from Mycobacterium tuberculosis has been cloned, expressed, purified and crystallized, and preliminary X-ray studies have been carried out on the crystals. The His-tagged tetrameric enzyme with a subunit molecular weight of 50.9 kDa crystallized with two tetramers in the asymmetric unit of the orthorhombic unit cell, space group P2(1)2(1)2(1). Molecular-replacement calculations and self-rotation calculations confirmed the space group and the tetrameric nature of the molecule.