Dynamic regulation of the INAD signaling scaffold becomes crystal clear.

PDZ domains are common building blocks of scaffold proteins that enhance specificity and speed in signal transduction cascades. Although PDZ modules are often viewed as passive participants, Mishra et al. (2007) now show that a PDZ domain in INAD, a scaffold protein in photoreceptor cells of the fruit fly, undergoes a light-dependent conformational change, which has important consequences for signaling and animal behavior.