Placement of 19F into the center of GB1: effects on structure and stability.

A structural and thermodynamic characterization of 5F-Trp-substituted immunoglobulin binding domain B1 of streptococcal protein G (GB1) was carried out by nuclear magnetic resonance and circular dichroism spectroscopy. A single fluorine reporter atom was positioned at the center of the three-dimensional structure, uniquely poised to be exploited for studying interior properties of this protein. We demonstrate that the introduction of 5F-Trp does not affect the global and local architecture of GB1 and has no influence on the thermodynamic stability. The favorable properties of the fluorinated GB1 render this molecule a desirable model system for the development of spectroscopic methodology and theoretical calculations.