Design of inhibitors: PDZ domains are conserved modules regulating the localization and activity of effector proteins. An integrated approach has been developed that uses peptide‐array screening technologies and fluorescence polarization measurements to analyze five promiscuous PDZ domains. By combining both methods, a highly specific inhibitor (iCAL3610=ANSRWPTSII) for one of the five PDZ domains was designed.

It pays to recycle! The most common mutation in cystic fibrosis (CF) impedes maturation and accelerates breakdown of the ion channel CFTR. A “stabilizer” has been characterized that blocks a PDZ domain responsible for CFTR degradation. The inhibitor iCAL36 extends the chloride channel's half‐life in airway epithelial cells. It also complements the activity of a corrector of the maturation defect, thus suggesting the potential for combination CF therapies.

Protein-protein interaction domains (PPIDs) are key elements in assembling functional protein complexes and controlling cellular activities. A major class of PPIDs is mediated by PDZ (for PSD-95, Dlg, ZO-1) domains [1][2][3], widespread scaffolding modules essential for regulating the localization and activity of numerous cellular effector proteins. Among the diverse protein interaction domains, PDZ domains are highly conserved in organisms from bacteria to humans [4]. They usually bind the C-terminus of their ligands.Consistent with their structural homology, PDZ domains exhibit overlapping recognition sequences, meaning that a given partner typically can interact with multiple domains. Some years ago, we proposed a general and efficient procedure for profiling PDZ-peptide interactions that provides a picture of specificity and selectivity covering the complete PDZligand sequence space by combining SPOT synthesis and K d prediction [5]. As expected, among the three PDZ domains that were analyzed (AF6, ERBIN and SNA1), the overlap of ligand sequences recognized at K d values between 50-100 μM was substantial. Recent studies have suggested that there is more diversity among PDZ sequence preferences than originally thought [6,7]. Nevertheless, the set of PDZ domains interacting with a given protein necessarily share overlapping binding motifs, and it remains challenging to develop a canonical peptide that will inhibit only a single PDZ domain out of this set.To address this issue, we focused on a set of five PDZ domains known to interact with the Cystic Fibrosis (CF) Transmembrane conductance Regulator (CFTR). The PDZ-containing proteins CAL (CFTR-Associated Ligand) [8,9] and its antagonists NHERF1 and NHERF2 (Na+/H+ Exchanger Regulatory Factor 1/2) [8,10], compete for the binding to CFTR. CAL contains one (CALP) and each NHERF protein two PDZ domains (N1P1, N1P2, N2P1 and N2P2) which control both the activity and the cell surface abundance of CFTR. NHERF family members increase CFTR activity at the apical membrane, whereas CAL promotes its lysosomal degradation. Thus, to explore novel therapeutic strategies for increasing the cellsurface abundance of CFTR, our goal was to design a selective inhibitor of the

Recycling lohnt sich! Die am häufigsten auftretende Mutation bei Mukoviszidose verhindert die Reifung und beschleunigt den Abbau des Ionenkanals CFTR. Ein Stabilisator wird vorgestellt, der eine für den CFTR‐Abbau verantwortliche PDZ‐Domäne blockiert. Der Hemmstoff iCAL36 verlängert die Halbwertszeit des Chloridkanals in bronchialen Epithelzellen. Er ergänzt außerdem die Aktivität eines Faltungskorrektors und erfüllt damit eine Voraussetzung für kombinierte Mukoviszidosetherapien.

Several proteases like the high temperature requirement A (HtrA) protein family containing internal or C-terminal PDZ domains play key roles in protein quality control in the cell envelope of Gram-negative bacteria. While several HtrA proteases have been extensively characterized, many features of C-terminal processing proteases such as tail-specific protease (Tsp) are still unknown. To fully understand these cellular control systems, individual domains need to be targeted by specific peptides acting as activators or inhibitors. Here, we describe the identification and design of potent inhibitors and activators of Tsp. Suitable synthetic substrates of Tsp were identified and served as a basis for the generation of boronic acid-based peptide inhibitors. In addition, a proteomic screen of E. coli cell envelope proteins using a synthetic peptide library was performed to identify peptides capable of amplifying Tsp's proteolytic activity. The implications of these findings for the regulation of PDZ proteases and for future mechanistic studies are discussed.