The work we have undertaken is to investigate the adsorption of two different proteins (BSA and BLG) having near same IEP and differing in their conformational flexibility, onto the surface of ZnS nanopartides (ZnS NPs). BSA and BLG both have an IEP value around pH similar to 5. BSA is more prone to conformational deformation and considered "soft" while BLG holds the conformational rigidity and considered as "hard" protein. To ascertain the differences in surface coverage and conformation of the protein onto ZnS surface (PZC similar to 3.7), we have evaluated the adsorption profile at pH 7, where the entire surface behaves negatively. An integrated approach was taken by incorporating zeta (zeta) potential, fluorescence and CD for analyzing the adsorption process. In both systems, an increase in protein surface coverage was observed with the increase in free protein concentration in the solution and zeta values approaching that of native protein at high surface coverage. An alteration in the tertiary structure was observed for both BSA and BLG. The CD spectra analysis reveals that the secondary structure of the BSA was more deviated from the native protein structure, accommodating the increased adsorption value. For BLG no such prominent structural alteration was observed. These findings help us to understand better, how adjustment of the protein adsorption amount can be achieved onto the surface of nanoparticles having like charges. (C) 2013 Elsevier Inc. All rights reserved.