LSD has a crystal structure, which means that scientists can track the way that x-ray beams reflect off of that structure to get a better sense of its shape. For instance, Roth's previous research demonstrated that LSD has a "lid," which makes it particularly sticky when it binds to a serotonin receptor. That's perhaps one reason, he suggested in 2017, that a trip can last hours.
In this study, Roth and colleagues used a technique called X-ray crystallography to examine how LSD binds to a protein on those serotonin receptors called Gαq, and even more specifically to one amino acid (a building block of that protein).
"This is the first time we see LSD bound to the protein in the brain which mediates the psychedelic actions of LSD," he says. "We actually found a single amino acid was essential for the actions of LSD and is found in only this particular receptor."
Ultimately, LSD settles into a "pocket" on the receptor and the looping helix shape of the protein begins to shift outwards (see the red arrows below).