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Phosphorylation-mimicking glutamate clusters in the proline-rich region are sufficient to simulate the functional deficiencies of hyperphosphorylated tau protein.

ABSTRACT: The microtubule-associated tau proteins represent a family of closely related phosphoproteins that become enriched in the axons during brain development. In Alzheimer's disease (AD), tau aggregates somatodendritically in paired helical filaments in a hyperphosphorylated form. Most of the sites that are phosphorylated to a high extent in paired helical filament tau are clustered in the proline-rich region (P-region; residues 172--251) and the C-terminal tail region (C-region; residues 368--441) that flank tau's microtubule-binding repeats. This might point to a role of a region-specific phosphorylation cluster for the pathogenesis of AD. To determine the functional consequences of such modifications, mutated tau proteins were produced in which a P- or C-region-specific phosphorylation cluster was simulated by replacement of serine/threonine residues with glutamate. We show that a phosphorylation-mimicking glutamate cluster in the P-region is sufficient to block microtubule assembly and to inhibit tau's interaction with the dominant brain phosphatase protein phosphatase 2A isoform AB alpha C. P-region-specific mutations also decrease tau aggregation into filaments and decrease tau's process-inducing activity in a cellular transfection model. In contrast, a phosphorylation-mimicking glutamate cluster in the C-region is neutral with regard to these activities. A glutamate cluster in both the P- and C-regions induces the formation of SDS-resistant conformational domains in tau and suppresses tau's interaction with the neural membrane cortex. The results indicate that modifications in the proline-rich region are sufficient to induce the functional deficiencies of tau that have been observed in AD. They suggest that phosphorylation of the proline-rich region has a crucial role in mediating tau-related changes during disease.

SUBMITTER: Eidenmuller J

PROVIDER: S-EPMC1222005 | biostudies-other | 2001 Aug

REPOSITORIES: biostudies-other

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Project description:The fungus Aspergillus fumigatus is a leading infectious killer in immunocompromised patients. Calcineurin, a calmodulin (CaM)-dependent protein phosphatase comprised of calcineurin A (CnaA) and calcineurin B (CnaB) subunits, localizes at the hyphal tips and septa to direct A. fumigatus invasion and virulence. Here we identified a novel serine-proline rich region (SPRR) located between two conserved CnaA domains, the CnaB-binding helix and the CaM-binding domain, that is evolutionarily conserved and unique to filamentous fungi and also completely absent in human calcineurin. Phosphopeptide enrichment and tandem mass spectrometry revealed the phosphorylation of A. fumigatus CnaA in vivo at four clustered serine residues (S406, S408, S410 and S413) in the SPRR. Mutation of the SPRR serine residues to block phosphorylation led to significant hyphal growth and virulence defects, indicating the requirement of calcineurin phosphorylation at the SPRR for its activity and function. Complementation analyses of the A. fumigatus ?cnaA strain with cnaA homologs from the pathogenic basidiomycete Cryptococcus neoformans, the pathogenic zygomycete Mucor circinelloides, the closely related filamentous fungi Neurospora crassa, and the plant pathogen Magnaporthe grisea, revealed filamentous fungal-specific phosphorylation of CnaA in the SPRR and SPRR homology-dependent restoration of hyphal growth. Surprisingly, circular dichroism studies revealed that, despite proximity to the CaM-binding domain of CnaA, phosphorylation of the SPRR does not alter protein folding following CaM binding. Furthermore, mutational analyses in the catalytic domain, CnaB-binding helix, and the CaM-binding domains revealed that while the conserved PxIxIT substrate binding motif in CnaA is indispensable for septal localization, CaM is required for its function at the hyphal septum but not for septal localization. We defined an evolutionarily conserved novel mode of calcineurin regulation by phosphorylation in filamentous fungi in a region absent in humans. These findings suggest the possibility of harnessing this unique SPRR for innovative antifungal drug design to combat invasive aspergillosis.

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Phosphorylation-mimicking glutamate clusters in the proline-rich region are sufficient to simulate the functional deficiencies of hyperphosphorylated tau protein.

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