Characterization of the Thermodynamic Stability of Neocarzinostatin

K.Jayachithra1, T.K.S.Kumar2, Ta-Jung Lu3, Chin Yu2*, and Der-Hang Chin1*

1.    Department of Chemistry, National Changhua University of Education, Changhua, Taiwan.

2.    Department of Chemistry, National Tsing Hua University, Hinschu, Taiwan.

3.    Department of Chemistry, National Chung-Hsing University, Taichung, Taiwan.


Neocarzinostatin (NCS) is a ~11.0KDa, DNA-nicking protein antibiotic isolated from Streptomyces carzinostaticus . The NCS holoprotein (holo-NCS) consists of a fluorescent chromophore which is tightly but noncovalently bound to the protein. Although NCS is a complex of the chromophore and the protein, the biologically active component of NCS is the chromophore. In pursuit of understanding the stability conferred on the protein by the chromophore, in the present study we investigate the thermodynamic stability of NCS under variety of conditions. Conformational stability of apoNCS at various pH conditions monitored using fluorescence spectroscopy revealed that the protein is stable in the pH range 3.0 to 5.0. The stability of the protein is found to decrease progressively with the increase in pH (Ph>5.0). Further, results of the urea denaturation experiments show that the free energy of the unfolding of the protein decreases significantly under alkaline conditions. These results would be elaborately discussed.