Phosphorylation of Human Tau Protein by Microtubule Affinity-Regulating Kinase 2

Abstract

Tau protein plays an important role in neuronal physiology and Alzheimer's neurodegeneration. Its abilities to aggregate abnormally, to bind to microtubules (MTs), and to promote MT assembly are all influenced by phosphorylation. Phosphorylation of serine residues in the KXGS motifs of Tau's repeat domain, crucial for MT interactions and aggregation, is facilitated most efficiently by microtubule-associated protein/microtubule affinity-regulating kinases (MARKs). Here we applied high-resolution nuclear magnetic resonance analysis to study the kinetics of phosphorylation of Tau by MARK2 and its impact on the structure and microtubule binding of Tau. We demonstrate that MARK2 binds to the N-terminal tail of Tau and selectively phosphorylates three major and five minor serine residues in the repeat domain and C-terminal tail. Structural changes induced by phosphorylation of Tau by MARK2 are highly localized in the proximity of the phosphorylation site and do not affect the global conformation, in contrast to phosphorylation in the proline-rich region. Furthermore, single-residue analysis of binding of Tau to MTs provides support for a model in which Tau's hot spots of MT interaction bind independently of each other and are differentially affected by phosphorylation.

Tau protein liquid–liquid phase separation can initiate tau aggregation

“…Moreover, by introducing minor levels of phosphorylation at specific sites in E. coli ‐derived recombinant tau441 by in vitro phosphorylation with kinase MARK2 (tau441 + MARK2) (Fig 3A and B), droplet formation could be rescued but at a much lower rate and with substantially smaller final droplet volumes of only ≈6 μm 3 (Fig 3D). In vitro tau phosphorylation by MARK2 specifically targets two major sites (S262 and S356) and two minor sites (S293 and S324) in the repeat domain and causes the physiological detachment of tau from microtubules (Timm et al , 2003; Schwalbe et al , 2013). For both tau441E17 and tau441 + MARK2, we observed droplet coagulation but not the formation of structured regions inside the droplets or on the droplet surface.…”

“…Phosphorylation of tau in or next to the MT binding region, for example, by MARK, reduces the affinity of tau to microtubules and causes its detachment. Small mostly local changes in the structure of the P2 domain and short peptide stretches in the repeat domain are thought to cause the loss of tau's binding capacity to assembled MTs (Schwalbe et al , 2013). This process is considered a normal physiological function of tau phosphorylation that is necessary to regulate MT stability.…”

Modulation of Intrinsically Disordered Protein Function by Post-translational Modifications

“…PTMs can regulate IDP function by (i) altering their steric, hydrophobic, or electrostatic properties due to primary structural effects (39); (ii) stabilizing, destabilizing, or even inducing secondary structural elements (24); and (iii) inhibiting/enhancing long-range tertiary contacts between distal motifs or PTM sites within the IDPs, or with interaction partners (40). PTMs can tune all aspects of IDPs, including the nature of the disordered ensemble (i.e.…”

The Ubiquitin-Proteasome System and Molecular Chaperone Deregulation in Alzheimer’s Disease

“…Numerous kinases are linked to Tau phosphorylation, both from proline-directed kinases and non-proline-directed kinases. The major known Tau kinases are GSK3, cyclindependent kinase 5 (CDK5), MAPKs, protein kinase A (PKA), protein kinase C (PKC), calcium/calmodulindependent protein kinase II (CaMKII), casein kinase II (CKII), MAP/microtubule-affinity-regulating kinases (MARKs), dual-specificity tyrosine-regulated kinase 1A (Dyrk1A), and the AMP-activated kinase (AMPK) [186,187,[217][218][219][220][221][222]. As a result of the diverse potential of phosphorylating enzymes, Tau phosphorylation can be a downstream of a myriad of events, including Ca 2+ -mediated toxicity [223,224], impaired insulin signaling [225,226], and brain metabolic deficiency [227].…”