agonist: a molecuse or entity that enhances or causes the stimulation of
antagonist: a molecule or entity that blocks or interferes with a process
ATD: The authors' wholly gratuitous shortening of 'amino terminal domain', simply referring to the folded portion of the protoin made up from a string of amino acids starting at the beginning (-NH2 group of the first amino acid)
chimera: something made of components drawn from several original. In the paper, the authors mix-and-match pieces of mouse and human sweet receptors to make a 'chimeric protein'. The original comes from Greek mythology, referring to a beastie with lion foreparts, spare goat head, and a tail that ends as a serpent.
competitive: in biochemical discussions, this refers to ONE WAY of being an antagonist. In this case, it refers to acting by directly blocking the binding of a competing molecule. A competitive inhibitor of BPG action would be a molecule that binds in DPG's site, but did not favor hemoglobin's oxygen-releasing conformation.
CRD: cysteine rich domain, as you might guess, a region of the protein rich in the amino acid cysteine. As you may recall from lab, cysteine has the unique property of readily forming covalent bonds between two cysteines. As you might guess, such linkages are much tougher than mere hydrogen bonds, greasy/hydrophobic interactions, etc. so serve to make a more stable, tougher protein.
domain: In protein folding discussions, this refers to a semi-autonomous folded unit, or something that looks and acts somewhat independently. Looking at your body, you might refer to your head domain, etc.--it's attached and part of the whole, but somewhat self-contained.
glycosylated: having attached sugar molecules (you'll see this root again when you study glycolysis--sugar splitting). Many proteins on self surfaces or in the environment are glycosylated as a form of protection/stabilization.
GPCR: G-protein coupled receptor; a protein that spans the membrane and is used to transfer information about the presence of signaling molecules on the OUTside to the cell cytoplasm. The receptor acts by being 'tweaked' on the outside, which causes it to interact with a traveling protein on the inside that has a GDP molecule which it then replaces with GTP. This causes a shape change, and the GTP-bearing molecule diffuses through the cell, spreading the news.
homodimer: made up of two identical units. In this case, referring to the fact that miraculin functions as a 'team' of two miraculin proteins that rarely or never separate, though they are held together by NON-covalent bonds. Hemoglobin is a HETEROtetramer--2 alpha globin + 2 beta-globin units
hT1R2-hT1R3: The name of the human 'sweet' taste receptor, so named to confuse undergrads forced to read papers about it
ligand: a small molecule, often NOT a protein, that is bound by a protein, often in order for the program to 'operate on it' or in order to influence the protein's conformation and activity
MCL: abbreviation used by the authors for miraculin protein
NCL: neoculin; a molecule the authors have previously characterized, but which is different in that it is always somewhat sweet, though enhanced by acidic pH. Bears no notable similarity to MCL in terms of amino acid sequence.
non-competitive: Acting through a mechanism OTHER THAN direct blocking. Example: BPG is a non-competitive inhibitor of oxygen binding to hemoglobin. It decreases hemoglobin affinity for oxygen INdirectly, not by fighting for oxygen's spot on heme.
pKa: The pH at which 50% of a particular group is ionized and 50% is not. For histidine, this occurs at about pH 6.0. Under such a condition, of all the histidines in a solution, at any given instant, about half would be positive in charge because a proton was attached to the 'vulnerable' nitrogen in the ring, and about 50% would be neutral without it. At another instant, the overall rate would still be about 50%, but which ones did and did not have a proton would be random.
TMD: The author's love affair with acronyms continues: trans-membrane domain; the part of a protein that goes THROUGH a membrane