I'm reading Mechanics of Motor Proteins and the Cytoskeleton by Jonathon Howard. It's written from a physicist's perspective; and in my opinion, it's a very thought-provoking graduate-level biophysics textbook. I thought I'd share the introduction to the third chapter, as Howard does a great job of motivating the question: "what are the material properties of proteins?"

The purpose of this chapter is to get a feeling for what proteins are like as mechanical devices. How rigid are they? How quickly do they move and change shape? And what is the quality of their motion: When a protein is struck by a force, does it ring like a tuning fork (underdamped motion), or does it creep monotonically into a new shape (overdamped motion)? To answer these questions, I begin this chapter with a discussion of the material properties of proteins [...] Proteins have similar densities and rigidities to hard plastics and Plexiglas. [...] Thus a protein, as a mechanical device, is like a little plastic toy.

Amazing. Get the book if you want more.