Atomic force microscopy reveals the mechanical design of a modular protein

Tandem modular proteins underlie the elasticity of natural adhesives, cell adhesion proteins, and muscle proteins. The fundamental unit of elastic pro teins is their individually folded modules. Here, we use protein engineerin g to construct multimodular proteins composed of Ig modules of different me chanical strength. We examine the mechanical properties of the resulting ta ndem modular proteins by using single protein atomic force microscopy. We s how that by combining modules of known mechanical strength, we can generate proteins with novel elastic properties. Our experiments reveal the simple mechanical design of modular proteins and open the way for the engineering of elastic proteins with defined mechanical properties, which can be used i n tissue and fiber engineering.