Protein stretching III: Force-extension curves of tethered bovine carbonicanhydrase B to the silicon substrate under native, intermediate and denaturing conditions

Atomic force microscope (AFM) was used to measure the force-extension relat ionship of the globular protein, carbonic anhydrase B, having 259 amino aci d residues; under native, denaturing and intermediate solution conditions. For this purpose, the protein was genetically engineered in order to endow it with -SH groups at its N- and C- termini and was fixed to the silanized surface of a silicon wafer using a covalent cross-linker with the reactive end to ISH and with a long spacer of polyethylene glycol. The silicon nitri de tip of the AFM was covered with a cross-linker with the reactive end to -SH and was brought into contact with the protein on the silicon surface. S ubsequent force curve measurements showed occasional stable bond formation, and the force extension relationship obtained from such curves showed dist inct characteristics of the native, denatured and intermediate forms of car bonic anhydrase B.