Structural study of hNck2 SH3 domain protein in solution by circular dichroism and X-ray solution scattering

We have done conformational study of hNck2 SH3 domain by means of far-ultraviolet (far-UV) circular dichroism (CD) and X-ray solution scattering (XSS). The results indicated that the following: (1) hNck2 SH3 domain protein exhibited concentration dependent monomer-dimer transition at neutral pH, while the secondary structure of this protein was independent of the protein concentration. (2) The hNck2 SH3 domain also exhibited pH dependent monomer-dimer transition. This monomer-dimer transition was accompanied with helix-β transition of the secondary structural change. Moreover, the acid-induced conformation, which was previously studied by Liu and Song by CD and nuclear magnetic resonance (NMR), was found to be not compact, but the conformation of the protein at acidic pH was similar to the cold denatured state (C-state) reported by Yamada et al. for equine β-lactoglobulin. We calculated that a structure of the equilibrium helix-rich intermediate of the hNck2 SH3 domain by DAMMIF program.

Structural change of hNck2 SH3 domain in solution.The blue circle is β-sheeted monomer. The red ellipse is helix-rich monomer.Highlights► hNck2 SH3 domain at neutral pH forms monomer and dimer depending on concentrations. ► The secondary structure is independent of the concentrations. ► At acidic pH, the protein forms helix-rich monomer even at high concentration. ► The helix-rich monomer is changed to β-sheeted dimer by pH increase. ► The helix-rich monomer at acidic pH is not compact.