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12 December 1998. Maas et al. (Abstract 2285) studied how phosphorylation of two different regions in tau proteins affects binding of tau protein to the plasma-membrane (PM). The two major phosphorylation sites studied were those located just upstream of the MT-binding repeats (whose phosphorylation can be monitored using the phosphorylation-dependent tau-1 antibody) and those downstream of the MT repeats (phosphorylation of which can be detected using the PHF-1 antibody). Their results indicate that the tau that binds to the PM is mainly tau-1 immunoreactive, and not PHF-1 immunoreactive. They then simulated phosphorylation in the two regions by substituting charged residues (glutamate in place of serine), and remarkably these two sets of mutants displayed selectivity of PM binding, with substitution of Glu residues in the C-terminal region inhibiting PM binding.
Ko et al. (Abstract 2286) investigated the role of tau glycation by raising an antibody specific for carboxymethyl-lysine (CML), the latter being a major glycoxidation product of advance glycation. The anti-CML antibody reacted with three major polypeptides of soluble PHF-tau preparations, but did not react with similar bands of PHF insoluble tau. Interestingly, PHF aggregates stained positively by immunogold labelling with the anti-CML antibody leading the investigators to conclude that tau-glycation probably occurs late in PHF formation.
Liao et al. (Abstract 2293) reported that protein phosphatase 1 (PP1) binds to the N-terminal 50-173 amino acid region of tau protein. They showed that PP1 colocalizes with both tau and MT in transfected cells. They also demonstrated that PP1 could dephosphorylate MAP2. They suggest that tau acts to target PP1 to microtubules where it may function in regulation of protein dephosphorylation.-June Kinoshita.
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