Synaptic Targeting and Function of SAPAPs Mediated by Phosphorylation-Dependent Binding to PSD-95 MAGUKs

The PSD-95/SAPAP/Shank complex functions as the major scaffold in orchestrating the formation and plasticity of the post-synaptic densities (PSDs). We previously demonstrated that the exquisitely specific SAPAP/Shank interaction is critical for Shank synaptic targeting and Shank-mediated synaptogenesis. Here, we show that the PSD-95/SAPAP interaction, SAPAP synaptic targeting, and SAPAP-mediated synaptogenesis require phosphorylation of the N-terminal repeat sequences of SAPAPs. The atomic structure of the PSD-95 guanylate kinase (GK) in complex with a phosphor-SAPAP repeat peptide, together with biochemical studies, reveals the molecular mechanism underlying the phosphorylation-dependent PSD-95/SAPAP interaction, and it also provides an explanation of a PSD-95 mutation found in patients with intellectual disabilities. Guided by the structural data, we developed potent non-phosphorylated GK inhibitory peptides capable of blocking the PSD-95/SAPAP interaction and interfering with PSD-95/SAPAP-mediated synaptic maturation and strength. These peptides are genetically encodable for investigating the functions of the PSD-95/SAPAP interaction in vivo. Using structural biology, cell biology, and electrophysiology approaches, Zhu et al. demonstrate that phosphorylation of the N-terminal repeating sequences of SAPAPs is required for the SAPAP/PSD-95 complex formation and SAPAP's synaptic targeting and maturation functions. They also developed a potent non-phosphorylated PSD-95 GK inhibitory peptide that can effectively disrupt the SAPAP/PSD-95 complex formation and thus inhibit excitatory synaptic activities. Keywords: GK domain; PSD-95; SAPAP; MAGUK; postsynaptic density; synaptic scaffold proteins; synaptogenesis; synaptic plasticit

Structural analyses of key features in the KANK1·KIF21A complex yield mechanistic insights into the cross-talk between microtubules and the cell cortex

The cross-talk between dynamic microtubules and the cell cortex plays important roles in cell division, polarity, and migration. A critical adaptor that links the plus ends of microtubules with the cell cortex is the KANK N-terminal motif and ankyrin repeat domains 1 (KANK1)/kinesin family member 21A (KIF21A) complex. Genetic defects in these two proteins are associated with various cancers and developmental diseases, such as congenital fibrosis of the extraocular muscles type 1. However, the molecular mechanism governing the KANK1/KIF21A interaction and the role of the conserved ankyrin (ANK) repeats in this interaction are still unclear. In this study, we present the crystal structure of the KANK1 center dot KIF21A complex at 2.1 angstrom resolution. The structure, together with biochemical studies, revealed that a five-helix-bundle-capping domain immediately preceding the ANK repeats of KANK1 forms a structural and functional supramodule with its ANK repeats in binding to an evolutionarily conserved peptide located in the middle of KIF21A. We also show that several missense mutations present in cancer patients are located at the interface of the KANK1 center dot KIF21A complex and destabilize its formation. In conclusion, our study elucidates the molecular basis underlying the KANK1/KIF21A interaction and also provides possible mechanistic explanations for the diseases caused by mutations in KANK1 and KIF21A.National Natural Science Foundation of China [31470733, U1532121]; Shanghai Municipal Science and Technology Commission, China ("Yang-Fan program") Grant [14YF1406700]; Strategic Priority Research Program of the Chinese Academy of Sciences [XDB08030104]12 month embargo; published online: 20 November 2017This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Structure of BAI1/ELMO2 complex reveals an action mechanism of adhesion GPCRs via ELMO family scaffolds

Brain-specific angiogenesis inhibitor (BAI) is an adhesion G protein-coupled receptor that acts through the ELMO/DOCK/Rac signaling pathway. Here the authors provide molecular insights into BAI/ELMO interactions by solving the crystal structure of the C-terminal cytoplasmic tail of BAI bound to the RAE tandem domains of ELMO2

Molecular insights into the MCM8/9 helicase complex in DNA unwinding and translocation

AbstractThe minichromosome maintenance protein 8 and 9 (MCM8 and MCM9) form a functional helicase complex (MCM8/9) that plays an essential role in DNAhomologous recombination (HR) repair for DNA double-strand break. However, the assembly mechanism and the structural characterization of MCM8/9 remain unclear. Here, we report structures of the MCM8/9 complex combining X-ray crystallography and cryo-electron microscopy reconstruction analysis. The structures reveal that MCM8/9 is arranged by a 3-fold symmetry axis to form a heterohexamer with a central channel to accommodate DNA. Multiple characteristic hairpins from the N-terminal oligosaccharide/oligonucleotide (OB) domains of MCM8/9 hexameric ring protrude to the central channel and serve to unwind the duplex DNA. Importantly, the MCM8/9 hexamer is consisted of an N-tier ring and a C-tier ring that are connected by the flexible linkers (N-C linkers) which are much longer than those of MCM2-7. Our structural dynamic analyses based on the cryo-EM data reveal that the flexible C-tier ring showed rotating motions relative to the N-tier ring, which maybe mediated by the N-C linkers as shorten the length of the N-C linkers will greatly decrease the helicase activity and chemoresistance of MCM8/9. Our structural and biochemical results implicate an unusual DNA unwinding and translocation mechanism of MCM8/9 helicase complex in HR.</jats:p