Model of the Brain Tumor-Pumilio translation repressor complex

The Brain Tumor (Brat) protein is recruited to the 3' untranslated region (UTR) of hunchback mRNA to regulate its translation. Recruitment is mediated by interactions between the Pumilio RNA-binding Puf repeats and the NHL domain of Brat, a conserved structural motif present in a large family of growth regulators. In this report, we describe the crystal structure of the Brat NHL domain and present a model of the Pumilio-Brat complex derived from in silico docking experiments and supported by mutational analysis of the protein-protein interface. A key feature of the model is recognition of the outer, convex surface of the Pumilio Puf domain by the top, electropositive face of the six-bladed Brat beta-propeller. In particular, an extended loop in Puf repeat 8 fits in the entrance to the central channel of the Brat beta-propeller. Together, these interactions are likely to be prototypic of the recruitment strategies of other NHL-containing proteins in development.