Human Fyn blocking peptide

Soluble oligomeric species of the amyloid-beta (A beta) peptide exhibit pronounced neurotoxic effects in Alzheimer's disease. Recent studies have indicated that the prion protein (PrP) is one of the cell-surface receptors, so-called a bad receptor, of A beta oligomers that mediates downstream cellular toxicity. A rational classification of A beta oligomers on the basis of conformation indicates that there are two distinct types of oligomers, namely, prefibrillar and fibrillar oligomers that are positive to A11 and OC conformation-dependent antibodies, respectively. The mechanism of heterotypic assembly of conformationally distinct oligomers and PrP is poorly understood. In this work, using an array of biophysical and biochemical tools, we dissect the molecular mechanism of the interaction of A11- and OC-positive A beta 42 oligomers with human PrP. Using site-specific binding titrations, we show that the recruitment of A beta oligomers primarily occurs via the electrostatic interaction between the N-terminal intrinsically disordered region of PrP and A beta oligomers. Our results demonstrate that OC-positive fibrillar oligomers possessing in-register parallel beta-sheet packing displayed similar to 30 times stronger binding with PrP compared to A11-positive oligomers. We also show that these OC-positive oligomers exacerbate their toxic effects on mammalian cells upon binding to PrP. On the contrary, the addition of PrP does not alter the toxicity exhibited by A11-positive oligomers. Our findings suggest that strategies targeting the interaction between PrP and OC-positive oligomers, which have been shown to be highly concentrated in the vicinity of amyloid plaques, may have therapeutic potential against Alzheimer's disease.

Kalirin7 (Kal7), a postsynaptic Rho GDP/GTP exchange factor (RhoGEF), plays a crucial role in long-term potentiation and in the effects of cocaine on behavior and spine morphology. The KALRN gene has been linked to schizophrenia and other disorders of synaptic function. Mass spectrometry was used to quantify phosphorylation at 26 sites in Kal7 from individual adult rat nucleus accumbens and prefrontal cortex before and after exposure to acute or chronic cocaine. Region- and isoform-specific phosphorylation was observed along with region-specific effects of cocaine on Kal7 phosphorylation. Evaluation of the functional significance of multisite phosphorylation in a complex protein like Kalirin is difficult. With the identification of five tyrosine phosphorylation (pY) sites, a panel of 71 SH2 domains was screened, identifying subsets that interacted with multiple pY sites in Kal7. In addition to this type of reversible interaction, endoproteolytic cleavage by calpain plays an essential role in long-term potentiation. Calpain cleaved Kal7 at two sites, separating the N-terminal domain, which affects spine length, and the PDZ binding motif from the GEF domain. Mutations preventing phosphorylation did not affect calpain sensitivity or GEF activity; phosphomimetic mutations at specific sites altered protein stability, increased calpain sensitivity, and reduced GEF activity.