Mechanical design of proteins-studied by single-molecule force spectroscopy and protein engineering

Mechanical unfolding and refolding may regulate the molecular elasticity of modular proteins with mechanical functions. The development of the atomic force microscopy (AFM) has recently enabled the dynamic measurement of thes e processes at the single-molecule level. Protein engineering techniques al low the construction of homomeric polyproteins for the precise analysis of the mechanical unfolding of single domains. alpha -Helical domains are mech anically compliant, whereas beta -sandwich domains, particularly those that resist unfolding with backbone hydrogen bonds between strands perpendicula r to the applied force, are more stable and appear frequently in proteins s ubject to mechanical forces. The mechanical stability of a domain seems to be determined by its hydrogen bonding pattern and is correlated with its ki netic stability rather than its thermodynamic stability. Force spectroscopy using AFM promises to elucidate the dynamic mechanical properties of a wid e variety of proteins at the single molecule level and provide an important complement to other structural and dynamic techniques (e.g., X-ray crystal lography, NMR spectroscopy, patch-clamp). (C) 2000 Elsevier Science Ltd. Al l rights reserved.