Gauging a Hydrocarbon Ruler by an Intrinsic Exciton Probe
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- 作者：M. Adil Khan ; Chris Neale ; Catherine Michaux ; Ré ; gis Pomè ; s ; Gilbert G. Privé ; Robert W. Woody ; Russell E. Bishop
- 刊名：Biochemistry
- 出版年：2007
- 出版时间：April 17, 2007
- 年：2007
- 卷：46
- 期：15
- 页码：4565 - 4579
- 全文大小：720K
- 年卷期：v.46,no.15(April 17, 2007)
- ISSN：1520-4995
文摘
The structural basis of lipid acyl-chain selection by membrane-intrinsic enzymes is poorlyunderstood because most integral membrane enzymes of lipid metabolism have proven refractory to structuredetermination; however, robust enzymes from the outer membranes of Gram-negative bacteria are nowproviding a first glimpse at the underlying mechanisms. The methylene unit resolution of the phospholipid:lipid A palmitoyltransferase PagP is determined by the hydrocarbon ruler, a 16-carbon saturated acyl-chain-binding pocket buried within the transmembrane 
-barrel structure. Substitution of Gly88 liningthe floor of the hydrocarbon ruler with Ala or Met makes the enzyme select specifically 15- or 12-carbonsaturated acyl chains, respectively, indicating that hydrocarbon ruler depth determines acyl-chain selection.However, the Gly88Cys PagP resolution does not diminish linearly because it selects both 14- and 15-carbon saturated acyl chains. We discovered that an exciton, emanating from a buried Tyr26-Trp66phenol-indole interaction, is extinguished by a local structural perturbation arising from the proximalGly88Cys PagP sulfhydryl group. Site-specific S-methylation of the single Cys afforded Gly88Cys-S-methyl PagP, which reasserted both the exciton and methylene unit resolution by specifically selecting13-carbon saturated acyl chains for transfer to lipid A. Unlike the other Gly88 substitutions, the Cyssulfhydryl group recedes from the hydrocarbon ruler floor and locally perturbs the subjacent Tyr26 andTrp66 aromatic rings. The resulting hydrocarbon ruler expansion thus occurs at the exciton's expense andaccommodates an extra methylene unit in the selected acyl chain. The hydrocarbon ruler-excitonjuxtaposition endows PagP with a molecular gauge for probing the structural basis of lipid acyl-chainselection in a membrane-intrinsic environment.
-barrel structure. Substitution of Gly88 liningthe floor of the hydrocarbon ruler with Ala or Met makes the enzyme select specifically 15- or 12-carbonsaturated acyl chains, respectively, indicating that hydrocarbon ruler depth determines acyl-chain selection.However, the Gly88Cys PagP resolution does not diminish linearly because it selects both 14- and 15-carbon saturated acyl chains. We discovered that an exciton, emanating from a buried Tyr26-Trp66phenol-indole interaction, is extinguished by a local structural perturbation arising from the proximalGly88Cys PagP sulfhydryl group. Site-specific S-methylation of the single Cys afforded Gly88Cys-S-methyl PagP, which reasserted both the exciton and methylene unit resolution by specifically selecting13-carbon saturated acyl chains for transfer to lipid A. Unlike the other Gly88 substitutions, the Cyssulfhydryl group recedes from the hydrocarbon ruler floor and locally perturbs the subjacent Tyr26 andTrp66 aromatic rings. The resulting hydrocarbon ruler expansion thus occurs at the exciton's expense andaccommodates an extra methylene unit in the selected acyl chain. The hydrocarbon ruler-excitonjuxtaposition endows PagP with a molecular gauge for probing the structural basis of lipid acyl-chainselection in a membrane-intrinsic environment.