The CAP-Gly of p150: one domain, two diseases, and a function at the end.

In this issue of Neuron, work from Moughamian and Holzbaur (2012) and Lloyd et al. (2012) reveals a role for p150 in initiation of retrograde transport at synaptic terminals. These studies also suggest how mutations of p150's CAP-Gly domain lead to both Perry syndrome and HMN7B disease.

Light-induced recruitment of INAD-signaling complexes to detergent-resistant lipid rafts in Drosophila photoreceptors.

Here, we reveal a novel feature of the dynamic organization of signaling components in Drosophila photoreceptors. We show that the multi-PDZ protein INAD and its target proteins undergo light-induced recruitment to detergent-resistant membrane (DRM) rafts. Reduction of ergosterol, considered to be a key component of lipid rafts in Drosophila, resulted in a loss of INAD-signaling complexes associated with DRM fractions. Genetic analysis demonstrated that translocation of INAD-signaling complexes to DRM rafts requires activation of the entire phototransduction cascade, while constitutive activation of the light-activated channels resulted in recruitment of complexes to DRM rafts in the dark. Mutations affecting INAD and TRP showed that PDZ4 and PDZ5 domains of INAD, as well as the INAD-TRP interaction, are required for translocation of components to DRM rafts. Finally, selective recruitment of phosphorylated, and therefore activatable, eye-PKC to DRM rafts suggests that DRM domains are likely to function in signaling, rather than trafficking.

Two stages of light-dependent TRPL-channel translocation in Drosophila photoreceptors.

Transient receptor potential (TRP) channels across species are expressed in sensory receptor cells, and often localized to specialized subcellular sites. In Drosophila photoreceptors, TRP-like (TRPL) channels are localized to the signaling compartment, the rhabdomere, in the dark, and undergo light-induced translocation into the cell body as a mechanism for long-term light-adaptation. We show that translocation of TRPL channels occurs in two distinct stages, first to the neighboring stalk membrane then to the basolateral membrane. In the first stage, light-induced translocation occurs within 5 minutes, whereas the second stage takes over 6 hours. The exclusive apical localization of TRPL channels in the first stage of translocation suggests that channels are released from the rhabdomere and diffuse laterally through the membrane into the adjoining stalk membrane. In the second stage, TRPL channels are localized in the basolateral membrane, implicating a different transport mechanism. Genetic analyses suggest that activation of the other light-activated TRP channel and eye-protein-kinase C (eye-PKC) are both required for the second stage of TRPL translocation in R1 to R6 photoreceptor cells, whereas only phospholipase C (PLC) is required for the first stage. Finally, we show that arrestin2 is required for the rhabdomeric localization and stability of TRPL channels.

Structure of human brain fructose 1,6-(bis)phosphate aldolase: linking isozyme structure with function.

Fructose-1,6-(bis)phosphate aldolase is a ubiquitous enzyme that catalyzes the reversible aldol cleavage of fructose-1,6-(bis)phosphate and fructose 1-phosphate to dihydroxyacetone phosphate and either glyceral-dehyde-3-phosphate or glyceraldehyde, respectively. Vertebrate aldolases exist as three isozymes with different tissue distributions and kinetics: aldolase A (muscle and red blood cell), aldolase B (liver, kidney, and small intestine), and aldolase C (brain and neuronal tissue). The structures of human aldolases A and B are known and herein we report the first structure of the human aldolase C, solved by X-ray crystallography at 3.0 A resolution. Structural differences between the isozymes were expected to account for isozyme-specific activity. However, the structures of isozymes A, B, and C are the same in their overall fold and active site structure. The subtle changes observed in active site residues Arg42, Lys146, and Arg303 are insufficient to completely account for the tissue-specific isozymic differences. Consequently, the structural analysis has been extended to the isozyme-specific residues (ISRs), those residues conserved among paralogs. A complete analysis of the ISRs in the context of this structure demonstrates that in several cases an amino acid residue that is conserved among aldolase C orthologs prevents an interaction that occurs in paralogs. In addition, the structure confirms the clustering of ISRs into discrete patches on the surface and reveals the existence in aldolase C of a patch of electronegative residues localized near the C terminus. Together, these structural changes highlight the differences required for the tissue and kinetic specificity among aldolase isozymes.

Light-dependent subcellular translocation of Gqalpha in Drosophila photoreceptors is facilitated by the photoreceptor-specific myosin III NINAC.

We examine the light-dependent subcellular translocation of the visual G(q)alpha protein between the signaling compartment, the rhabdomere and the cell body in Drosophila photoreceptors. We characterize the translocation of G(q)alpha and provide the first evidence implicating the involvement of the photoreceptor-specific myosin III NINAC in G(q)alpha transport. Translocation of G(q)alpha from the rhabdomere to the cell body is rapid, taking less than 5 minutes. Higher light intensities increased the quantity of G(q)alpha translocated out of the rhabdomeres from 20% to 75%, consistent with a mechanism for light adaptation. We demonstrate that translocation of G(q)alpha requires rhodopsin, but none of the known downstream phototransduction components, suggesting that the signaling pathway triggering translocation occurs upstream of G(q)alpha. Finally, we show that ninaC mutants display a significantly reduced rate of G(q)alpha transport from the cell body to the rhabdomere, suggesting that NINAC might function as a light-dependent plus-end motor involved in the transport of G(q)alpha.