Cyclic Tau-derived peptides for stabilization of microtubules

Microtubule stabilising peptides: new paradigm towards management of neuronal disorders

Neuronal cells made of soma, axon, and dendrites are highly compartmentalized and possess a specialized transport system that can convey long-distance electrical signals for the cross-talk. The transport system is made up of microtubule (MT) polymers and MT-binding proteins. MTs play vital and diverse roles in various cellular processes. Therefore, defects and dysregulation of MTs and their binding proteins lead to many neurological disorders as exemplified by Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, Huntington's disease, and many others. MT-stabilising agents (MSAs) altering the MT-associated protein connections have shown great potential for several neurodegenerative disorders. Peptides are an important class of molecules with high specificity, biocompatibility and are devoid of side effects. In the past, peptides have been explored in various neuronal disorders as therapeutics. Davunetide, a MT-stabilising octapeptide, has entered into phase II clinical trials for schizophrenia. Numerous examples of peptides emerging as MSAs reflect the emergence of a new paradigm for peptides which can be explored further as drug candidates for neuronal disorders. Although small molecule-based MSAs have been reviewed in the past, there is no systematic review in recent years focusing on peptides as MSAs apart from davunetide in 2013. Therefore, a systematic updated review on MT stabilising peptides may shed light on many hidden aspects and enable researchers to develop new therapies for diseases related to the CNS. In this review we have summarised the recent examples of peptides as MSAs.

Rational Discovery of Microtubule-Stabilizing Peptides

Microtubule (MT) stabilization is an attractive pharmacological strategy to hamper the progress of neurodegenerative diseases. In this regard, seeking peptides with MT-stabilizing properties has awoken great interest. This work reports the rational discovery of two structurally related MT-stabilizing octapeptides using a combination of protein-peptide docking, conventional molecular dynamics, Gaussian accelerated molecular dynamics (GaMD), and tubulin polymerization assays. FASTA sequences for ∼1000 peptides were crafted from single and double mutants of davunetide (NAP) and docked against the Taxol (TX) site on an octameric MT model representing a portion of the MT wall. Docked peptides were rescored after MM minimization and binding free energy refinement through single-point MM/GBSA calculations. The 60 best-ranked peptides were subjected to 50 ns MD simulations on peptide-MT complexes at the terminal TX site in the octameric Tau-MT model resulting in 11 complexes with occupancies greater than 99% and peptide-protein binding free energies less than -40 kcal/mol. Selected peptides were then examined through 300 ns GaMD simulations in complexes containing two identical ligands at the terminal and intermediate TX sites in the Tau-MT model to account for the differential association of MT-binding peptides to different regions of the MT structure. Six candidates showed a favorable MT-binding potential based on the analysis of interaction frequencies and relative mobilities of the complex components, suggesting a pivotal role of Arg278, Gln281, and Arg369 residues for peptides recognition. Four candidates were predicted to preserve an adequate balance of longitudinal and lateral interactions between tubulin dimers in peptide-MT complexes such that MT-stabilizing effects could be expected. MT polymerization experiments confirmed that four peptides (HAPVSIHQ, NYPVSIHQ, NWPVSIWQ, HAPVSIIQ) exhibit MT-stabilizing activity in vitro with NWPVSIWQ (P43) and HAPVSIIQ (P52) being the most active. Tryptophan quenching assays verified that P43 and P52 bind to nonpolymeric tubulin, whereas viability experiments on HEK cells confirmed their safety to pursue future pharmacological studies. The results herein presented are valuable to making progress in the rational design of MT-stabilizing peptides.

Generation of stable microtubule superstructures by binding of peptide-fused tetrameric proteins to inside and outside

Microtubules play important roles in biological functions by forming superstructures, such as doublets and branched structures, in vivo. Despite the importance, it is challenging to construct these superstructures in vitro. Here, we designed a tetrameric fluorescent protein Azami-Green (AG) fused with His-tag and Tau-derived peptide (TP), TP-AG, to generate the superstructures. Main binding sites of TP-AG can be controlled to the inside and outside of microtubules by changing the polymerization conditions. The binding of TP-AG to the inside promoted microtubule formation and generated rigid and stable microtubules. The binding of TP-AG to the outside induced various microtubule superstructures, including doublets, multiplets, branched structures, and extremely long microtubules by recruiting tubulins to microtubules. Motile microtubule aster structures were also constructed by TP-AG. The generation of various microtubule superstructures by a single type of exogenous protein is a new concept for understanding the functions of microtubules and constructing microtubule-based nanomaterials.

Light-induced stabilization of microtubules by photo-crosslinking of a Tau-derived peptide

For light-induced stabilization of microtubules (MTs) to manipulate cells, a photo-reactive diazirine group was conjugated to a Tau-derived peptide, a motif binding on the inside of MTs. Ultraviolet (UV) light irradiation induced significant stabilization of MTs via the formation of a covalent bond of the peptide and showed toxicity.

Encapsulation of Nanomaterials Inside Microtubules by Using a Tau-Derived Peptide

Microtubules (MTs) are tubular cytoskeletons, which are used for the various applications such as active matters and therapeutic targets. Although modification of the exterior surface of MTs is frequently used for functionalization of MTs, there was no approach to introduce molecules inside MTs. We previously developed a unique peptide binding to the inner surface of MT, which is derived from a MT-associated protein, Tau. The Tau-derived peptide (TP) can be used to introduce various nanomaterials inside MTs. Here we describe the TP-based encapsulation of fluorescent dye, gold nanoparticle, green fluorescent protein, and magnetic CoPt nanoparticles inside MTs.

On the Microtubule-Stabilizing Properties of a Tau Oligopeptide

Preserving the integrity of neuronal microtubules (MTs) has emerged as a promising strategy to inhibit the progression of neurodegenerative disorders such as Alzheimer's disease. Such a goal could be achieved by peptides that mimic the functional role of Tau, an MT-associated protein that stabilizes MTs by dynamically binding to their outer surface. This work examines the binding properties and MT-stabilizing potential of a 27-amino acid Tau oligopeptide from 300 ns Gaussian-accelerated molecular dynamics simulations and Molecular Mechanics/Generalized Born Surface Area (MM/GBSA) calculations on octameric MT models bound to two equivalent and independent Tau peptides. Bound peptides adopted extended conformations that are highly consistent with cryo-electron microscopy reports for full-length Tau bound to MTs. Anchoring points in three consecutive tubulin subunits were identified, with a relevant contribution of the Ser419-Val435 region to α-tubulin. Tau peptides strengthen the longitudinal protein-protein contacts within the MT lattice and exert a cooperative MT-stabilizing effect in MT complexes simultaneously bonded to taxol or peloruside A. Ser phosphorylation results in a larger peptide mobility, altered interaction profiles, and MT destabilization, which are in line with the loss of MT integrity resulting from the post-translational hyperphosphorylation of Tau. Our results shed light on the MT-stabilizing potential of Tau-mimetic peptides to act as novel neuroprotective agents targeting MTs.

Live-Cell Fluorescence Imaging of Microtubules by Using a Tau-Derived Peptide

Microtubules (MTs) are important targets for imaging in living cells because of their vital roles in cellular processes. The dynamics (polymerization/depolymerization) of MTs has been imaged in living cells by utilizing MT-targeted drugs as scaffolds. We previously developed a unique MT-binding motif derived from a MT-associated protein, Tau. The Tau-derived peptide (TP) binds to the inner surface of MTs without inhibiting the dynamics of MTs. We introduce a new protocol for live-cell imaging of MTs by using fluorescently labeled TP. We exemplify that tetramethylrhodamine (TMR)-labeled TP (TP-TMR) is spontaneously internalized into HepG2 cells and binds to intracellular MTs, enabling visualization of MTs in living cells. TP-TMR shows no apparent effects on polymerization/depolymerization of MTs and no cytotoxicity. Thus, the peptide-based approach is useful for long-term imaging of MTs.