Inhaled Anesthetics Promote Albumin Dimerization through Reciprocal Exchange of Subdomains

Abstract

Inhaled anesthetics affect protein-protein interaction, but the mechanisms underlying these effects are still poorly understood. We examined the impact of sevoflurane and isoflurane on the dimerization of human serum albumin (HSA), a protein with anesthetic binding sites that are well characterized. Intrinsic fluorescence emission was analyzed for spectral shifting and self-quenching, and control first derivatives (spectral responses to changes in HSA concentration) were compared against those obtained from samples treated with sevoflurane or isoflurane. Sevoflurane increased dimer-dependent self-quenching and both decreased oligomer-dependent spectral shifting, suggesting that inhaled anesthetics promoted HSA dimerization. Size exclusion chromatography and polarization data were consistent with these observations. The data support the proposed model of a reciprocal exchange of subdomains to form an HSA dimer. The open-ended exchange of subdomains, which we propose occuring in HSA oligomers, was inhibited by sevoflurane and isoflurane.

Protection Against Protein Aggregation by Alpha-Crystallin as a Mechanism of Preconditioning

“…We know that aB-crystallin protects against hypertonic stress [24]. Furthermore, a-crystallin has an additional moonlighting function as an antiglycation agent [25], which is consistent with the previously observed increase in aldehydic modification of proteins exposed to inhaled anesthetics [4,5,26], suggesting that anesthetic preconditioning may confer protection against future glycation stress. The mechanism of isoflurane-induced protein misfolding seen previously [3] may involve a localized dehydration of protein, which consequently may increase the susceptibility to aggregation.…”

“…Isoflurane upregulates many heat shock genes in SH-SY5Y cells, showing an early and delayed response [3]. We think that these responses to isoflurane are due to effects on protein conformation [4,5]. Several of the upregulated heat shock genes are considered late responders: DNAJC5G, CRYAA and HSPB2 [3].…”

“…The mechanism of isoflurane-induced protein misfolding seen previously [3] may involve a localized dehydration of protein, which consequently may increase the susceptibility to aggregation. Upon binding and release, there may be a desolvation or change in the hydration at the isoflurane binding site [27], resulting in altered protein conformation [3,5,26] and changes in protein-protein interaction [4]. Ethanol also displaces water from protein sites [28,29].…”

“…We previously showed that isoflurane exposure causes an upregulation of many heat shock genes in SH-SY5Y cells, demonstrating an early and delayed response [3]. The upregulation of molecular chaperone genes is presumably due to isoflurane's effect on protein conformation [4,5]. Several of the heat shock genes that are identified as late responders are of particular interest, such as those that are involved in promoting axonal and synaptic integrity [3].…”

Dynamic Oligomeric Properties

“…Interestingly, albumin forms dimers, trimers and higher order structures, and this process of oligomerization is concentration-dependent. The true nature of the arrangement of the monomer units within the larger oligomeric structures still remains a mystery, but it has been proposed that domain exchange occurs to stabilize competing oligomeric structures [142]. Dimerization involves a reciprocal Fig.…”