Telomerase adds telomeric repeats at chromosome ends to compensate for telomere loss caused by incomplete genome end replication1. In humans, telomerase is upregulated during embryogenesis and in cancers, while mutations that compromise its function result in diseases2. Our previous 8 Å human telomerase structure revealed vertebrate-specific composition and architecture3, consisting of a catalytic core flexibly tethered to an H/ACA ribonucleoprotein (RNP) lobe by telomerase RNA. To effectively modulate telomerase activity as a therapeutic approach against cancers and diseases, high-resolution structural information is necessary. Here we present the structure of human telomerase holoenzyme bound to a telomeric DNA, determined by cryo-electron microscopy (cryo-EM) at 3.4 Å resolution for the H/ACA RNP and 3.8 Å resolution for the catalytic core. The structure reveals crucial DNA/RNA binding interfaces in telomerase active site

Wiskott–Aldrich syndrome protein (WASP) activates the actin-related protein 2/3 homolog (Arp2/3) complex and regulates actin polymerization in a physiological setting. Cell division cycle 42 (Cdc42) is a key activator of WASP, which binds Cdc42 through a Cdc42/Rac-interactive binding (CRIB)-containing region that defines a subset of Cdc42 effectors. Here, using site-directed mutagenesis and binding affinity determination and kinetic assays, we report the results of an investigation into the energetic contributions of individual WASP residues to both the Cdc42–WASP binding interface and the kinetics of complex formation. Our results support the previously proposed dock-and-coalesce binding mechanism, initiated by electrostatic steering driven by WASP's basic region and followed by a coalescence phase likely driven by the conserved CRIB motif. The WASP basic region, however, appears also to play a role in the final complex, as its mutation affected both on- and off-rates, suggesting a more comprehensive physiological role for this region centered on the C-terminal triad of positive residues. These results highlight the expanding roles of the basic region in WASP and other CRIB-containing effector proteins in regulating complex cellular processes and coordinating multiple input signals. The data presented improve our understanding of the Cdc42–WASP interface and also add to the body of information available for Cdc42–effector complex formation, therapeutic targeting of which has promise for Ras-driven cancers. Our findings suggest that combining high-affinity peptide-binding sequences with short electrostatic steering sequences could increase the efficacy of peptidomimetic candidates designed to interfere with Cdc42 signaling in cancer.

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