Totally synthetic microperoxidase-11

Electrochemical Biosensors Employing Natural and Artificial Heme Peroxidases on Semiconductors

Heme peroxidases are widely used as biological recognition elements in electrochemical biosensors for hydrogen peroxide and phenolic compounds. Various nature-derived and fully synthetic heme peroxidase mimics have been designed and their potential for replacing the natural enzymes in biosensors has been investigated. The use of semiconducting materials as transducers can thereby offer new opportunities with respect to catalyst immobilization, reaction stimulation, or read-out. This review focuses on approaches for the construction of electrochemical biosensors employing natural heme peroxidases as well as various mimics immobilized on semiconducting electrode surfaces. It will outline important advances made so far as well as the novel applications resulting thereof.

Folding and Assembly of Vanilloid Receptor Secondary-Structure Peptide with Hexahistidine Linker at Nickel-Nitrilotriacetic Acid Monolayer for Capsaicin Recognition

Herein, we report the self-assembly of a synthetic vanilloid receptor (VR) peptide that selectively binds capsaicin. We synthesized a 26-mer peptide-YSEILFFVQS-HHHHHH-LAMGWTNMLY (S3HS4)-comprising two chemoreceptor domains of transient receptor potential channel (TRPV1) linked by a hexahistidine sequence. High-speed atomic force microscopy (AFM) imaging in water revealed that the peptide structures alternated rapidly between wedge shape and linear forms. Circular dichroism spectroscopy showed that 65% of the amide units in the peptide chain adopted an α-helix structure, which was ascribed to the chemoreceptor domains. S3HS4 developed well-packed monolayers at the Ni-treated thiolated nitrilotriacetic acid self-assembled monolayers by chelation of the hexahistidine segment, as characterized by infrared spectroscopy and AFM, which exhibited statistically constant specific height. Therefore, S3HS4 was expected to fold spontaneously upon chelation, and the resulting helix-turn-helix conformers developed films while uniformly oriented: the tilt angle was 69° from the surface normal to the substrate. According to microgravimetric analysis using a quartz crystal microbalance (QCM), the adsorption was 84 ± 47 pmol cm^-2 ( n = 3), which was almost consistent with the saturation adsorption of an α-helix unit. We also used a QCM to investigate the host-guest reactions of S3HS4 and found that the S3HS4-attached QCM-chip-bound capsaicin with an apparent binding constant of (4.2 ± 3.6) × 10⁴ M^-1 ( n = 4), whereas there was no evidence of binding to vanillin or acetophenone. Two controls-a blank chip without S3HS4 and a chip modified with a single helical peptide (LAMGWTNMLY-HHHHHH)-produced no capsaicin response. To the best of our knowledge, S3HS4 is the first example of a synthetic VR mimic peptide. We believe that the present surface-directed structure-based design can be used to exploit the α-helix bundle in hexahistidine-linked bishelical peptides.

A Novel Peroxidase Mimics and Ameliorates Alzheimer's Disease-Related Pathology and Cognitive Decline in Mice

Alzheimer's disease (AD) is the most common neurodegenerative disorder in the elderly, which is characterized by the accumulation of amyloid β (Aβ) plaques, oxidative stress, and neuronal loss. Therefore, clearing Aβ aggregates and reducing oxidative stress could be an effective therapeutic strategy for AD. Deuterohemin-AlaHisThrValGluLys (DhHP-6), a novel deuterohemin-containing peptide mimetic of the natural microperoxidase-11 (MP-11), shows higher antioxidant activity and stability compared to the natural microperoxidases. DhHP-6 possesses the ability of extending lifespan and alleviating paralysis in the Aβ1-42 transgenic Caenorhabditis elegans CL4176 model of AD, as shown in our previous study. Therefore, this study was aimed at exploring the neuroprotective effect of DhHP-6 in the APPswe/PSEN1dE9 transgenic mouse model of AD. DhHP-6 reduced the diameter and fiber structure of Aβ1-42 aggregation in vitro, as shown by dynamic light scattering and transmission electron microscope. DhHP-6 exerted its neuroprotective effect by inhibiting Aβ aggregation and plaque formation, and by reducing Aβ1-42 oligomers-induced neurotoxicity on HT22 (mouse hippocampal neuronal) and SH-SY5Y (human neuroblastoma) cells. In the AD mouse model, DhHP-6 significantly ameliorated cognitive decline and improved spatial learning ability in behavioral tests including the Morris water maze, Y-maze, novel object recognition, open field, and nest-building test. Moreover, DhHP-6 reduced the deposition of Aβ plaques in the cerebral cortex and hippocampus. More importantly, DhHP-6 restored the morphology of astrocytes and microglia, and significantly reduced the levels of pro-inflammatory cytokines. Our findings provide a basis for considering the non-toxic, peroxidase mimetic DhHP-6 as a new candidate drug against AD.