Aequorin

Aequorin is a

Apoaequorin, the protein portion of aequorin, is an ingredient in the dietary supplement Prevagen. The US Federal Trade Commission (FTC) has charged the maker with false advertising for its memory improvement claims.

Discovery

Work on aequorin began with

The crystal structure revealed that aequorin binds coelenterazine and oxygen in the form of a peroxide, coelenterazine-2-hydroperoxide.^[9] The binding site for the first two calcium atoms show a 20 times greater affinity for calcium than the third site.^[10] However, earlier claims that only two EF-hands bind calcium^[11] were questioned when later structures indicated that all three sites can indeed bind calcium.^[12] Thus, titration studies show that all three calcium-binding sites are active but only two ions are needed to trigger the enzymatic reaction.^[13]

Other studies have shown the presence of an internal

Chemical characterization of aequorin indicates the protein is somewhat resilient to harsh treatments. Aequorin is heat resistant.[15] Held at 95 °C for 2 minutes the protein lost only 25% activity. Denaturants such as 6-M urea or 4-M guanidine hydrochloride did not destroy the protein.

Genetics

Aequorin is presumably encoded in the genome of Aequorea. At least four copies of the gene were recovered as cDNA from the animal.^[16][17] Because the genome has not been sequenced, it is unclear if the cDNA variants can account for all of the isoforms of the protein.^[18]

Mechanism of action

Early studies of the bioluminescence of Aequorea by E. Newton Harvey had noted that the bioluminescence appears as a ring around the bell, and occurs even in the absence of air.^[19] This was remarkable because most bioluminescence reactions require oxygen, and led to the idea that the animals somehow store oxygen.^[20] It was later discovered that the apoprotein can stably bind coelenterazine-2-hydroperoxide, and oxygen is required for the regeneration to this active form of aequorin.^[21] However, in the presence of calcium ions, the protein undergoes a conformational change and converts its prosthetic group, coelenterazine-2-hydroperoxide, into excited coelenteramide and CO₂.^[22] As the excited coelenteramide relaxes to the ground state, blue light (wavelength of 465 nm) is emitted. Before coelenteramide is exchanged out, the entire protein is still fluorescent blue.^[23][24] because of the connection between bioluminescence and fluorescence, this property was ultimately important in the discovery of the luciferin coelenterazine.^[25]

Applications

Since the emitted light can be easily detected with a

Apoaequorin is an ingredient in "Prevagen", which is marketed by Quincy Bioscience as a memory supplement. In 2017, the US Federal Trade Commission (FTC) charged the maker with falsely advertising that the product improves memory, provides cognitive benefits, and is "clinically shown" to work.^[38] According to the FTC, "the marketers of Prevagen preyed on the fears of older consumers experiencing age-related memory loss". Quincy said that it would fight the charges.^[39][40][41]

Prior to the suit, a clinical trial run by researchers employed by Quincy Bioscience "found no overall benefit compared to a placebo for its primary endpoints involving memory and cognition", while the company's advertising misleadingly cited a few contested subgroup analyses that showed slight improvements.^[42][43]

The suit (Spath, et al. v. Quincy Bioscience Holding Company, Inc., et al., Case No. 18-cv-12416, D. NJ.) was dismissed in the District court, but an appeal seeking to overturn the dismissal was filed. The suit was consolidated with another against Quincy Pharmaceuticals, Vanderwerff v. Quincy Bioscience (Case No. 17-cv-784, D. NJ), which was the lead case.^[44]

On February 21, 2019, the United States Court of Appeals for the Second Circuit ruled that the FTC and the state of New York could proceed with their lawsuit against Quincy Bioscience for its claims that Prevagen can improve memory. The order came less than two weeks after the parties argued the case before a three-judge panel of the circuit, where company lawyers admitted they did not "dispute that if you look across the entire 211 people who completed the study there was no statistically significant difference". The court vigorously dismissed allegations by the company lawyers that the FTC pursued its action for political reasons.^[45][46]

On March 23, 2020, a federal magistrate judge in the United States District Court for the Southern District of Florida entered a report and recommendations certifying a nationwide class action for the class of consumers who purchased Prevagen over the previous four years.^[47] The trial in the case was set for October 2020.^[47][48]

As of September 21, 2020^[update] Quincy Bioscience agreed to settle the claims that it misrepresented its Prevagen products as supporting brain health and helping with memory loss. Under the terms of the settlement, eligible purchasers applying by October 26, 2020 for purchases made from 2007 through July 31, 2020 could recover refunds of up to $70. ^[49]

Dr.