DIRECT MEASUREMENT OF FORCES BETWEEN SELF-ASSEMBLED PROTEINS - TEMPERATURE-DEPENDENT EXPONENTIAL FORCES BETWEEN COLLAGEN TRIPLE HELICES

We report direct measurements of force vs. separation between self-ass embled proteins. These forces are observed between collagen triple hel ices in native and reconstituted fibers. They are a combination of a s hort-range repulsion, which varies exponentially over at least five de cay lengths, and an inferred, longer-ranged attraction responsible for spontaneous assembly. From 5-degrees-C to 35-degrees-C the relative c ontribution of the attraction to the net force increases with temperat ure. These forces are strikingly similar to the ''hydration'' forces m easured between several other linear macromolecules (DNA, polysacchari des) and between lipid bilayer membranes. The decay length of the repu lsive force agrees well with a theoretical estimate based on axial per iodicity of the triple helix, suggesting another connection between mo lecular architecture and protein-protein interaction.