Polymers exhibiting lower critical solution behavior in water have found broad use as thermoresponsive moieties in soft materials, particularly in biomedical applications for triggered actuation, gelation, accumulation, or release. In this work, changing the thermoresponsive block in a self-assembling hydrogel is shown to be a useful approach to control the viscoelastic behavior and mechanical reinforcement of the gel above its transition temperature. Triblock copolymers were prepared with artificial associative protein midblocks from either site-specific bioconjugation of narrowly disperse poly(N-isopropylacrylamide) (PNIPAM) or as biosynthetic genetic fusions to monodisperse elastin-like polypeptide (ELP) sequences. Both synthetic approaches yield responsively reinforceable hydrogels that can be stiffened by up to an order of magnitude to approximately 10(5) Pa at 30% (w/w). However, end block chemical composition and linear block copolymer architecture could be manipulated to yield high-temperature plateau moduli ranging from 64 to 260 kPa. In particular, a glycine to alanine mutation in the pentapeptide repeat of the ELP end blocks that is known to influence the secondary structure of the collapsed polypeptide is responsible for over a 3-fold increase in gel stiffness in the reinforced state. Mechanical spectroscopy reveals that end block chemical composition and linear block architecture lead to a nearly 50-fold difference in elastic energy storage at long time scales and at elevated temperatures. Nanostructure characterization and modeling suggest that end block design can affect gel mechanics by influencing micelle size, nanoscale morphology, and internal micellar structure. Thus, the selection of different thermoresponsive end block chemistries is a useful tool in programming the assembly and reinforcement of nanostructured hydrogels.