Inhaled Anesthetic Binding Sites in Human Serum Albumin

Abstract

Previous evidence suggests multiple anesthetic binding sites on human serum albumin, but to date, we have only identified Trp-214 in an interdomain cleft as contributing to a binding site. We used a combination of site-directed mutagenesis, photoaffinity labeling, amide hydrogen exchange, and tryptophan fluorescence spectroscopy to evaluate the importance to binding of a large domain III cavity and compare it to binding character of the 214 interdomain cleft. The data show anesthetic binding in this domain III cavity of similar character to the interdomain cleft, but selectivity for different classes of anesthetics exists. Occupancy of these sites stabilizes the native conformation of human serum albumin. The features necessary for binding in the cleft appear to be fairly degenerate, but in addition to hydrophobicity, there is evidence for the importance of polarity. Finally, myristate isosterically competes with anesthetic binding in the domain III cavity and allosterically enhances anesthetic binding in the interdomain cleft.

Geometric Isomers of a Photoactivable General Anesthetic Delineate a Binding Site on Adenylate Kinase

“…Our results are in partial agreement with a recent analysis that concluded that alcohol binding sites possess a hydrogen bond acceptor in a turn or loop often located near the Nterminal end of an ␣-helix (35). The location of anesthetic sites at the interface between two structural domains has been noted in some other cases (6,36) and may prove to be a common motif for general anesthetic binding sites.…”

Molecular Features of an Alcohol Binding Site in a Neuronal Potassium Channel

“…The physiological importance and molecular properties of such sites have been mainly inferred from the relationship between the narcotic effect and anesthetic solubility, studies with model soluble proteins, and theoretical arguments (5,9,(12)(13)(14)(15). Although it is clear that ion channels and other membrane proteins harbor relatively specific and relevant sites for general anesthetic agents (1-6), the physicochemical and molecular features of these sites are not wellunderstood.…”

“…The results of these studies are consistent with the presence of physically circumscribed hydrophobic protein cavities that constitute the alcohol and general anesthetic sites. Also, studies with soluble model proteins have examined the relationship between anesthetic solubility and anesthetic action along with structure-function analysis and thermodynamic arguments and suggest that polar interactions also contribute to the binding of alcohol and inhaled anesthetics (5,9,(12)(13)(14)(15). Polar interactions are also likely to contribute to the binding of general anesthetic agents to ion channels, which are critical physiological targets of these agents (including 1-alkanols).…”

Practical Aspects of the Ligand-Binding and Enzymatic Properties of Human Serum Albumin.

“…1D). Eckenhoff et al, 25) using solubilized HSA and rHSA mutants, observed that halothane, isoflurane, and 1-chloro-1,2,2-trifluorocyclobutane bind primarily in the interdomain cleft between IA and IIA ( Fig. 1A), which has 214 Trp as an important binding residue.…”