PagP Crystallized from SDS/Cosolvent Reveals the Route for Phospholipid Access to the Hydrocarbon Ruler

SummaryEnzymatic reactions involving bilayer lipids occur in an environment with strict physical and topological constraints. The integral membrane enzyme PagP transfers a palmitoyl group from a phospholipid to lipid A in order to assist Escherichia coli in evading host immune defenses during infection. PagP measures the palmitoyl group with an internal hydrocarbon ruler that is formed in the interior of the eight-stranded antiparallel β barrel. The access and egress of the palmitoyl group is thought to take a lateral route from the bilayer phase to the barrel interior. Molecular dynamics, mutagenesis, and a 1.4 Å crystal structure of PagP in an SDS / 2-methyl-2,4-pentanediol (MPD) cosolvent system reveal that phospholipid access occurs at the crenel present between strands F and G of PagP. In this way, the phospholipid head group can remain exposed to the cell exterior while the lipid acyl chain remains in a predominantly hydrophobic environment as it translocates to the protein interior.

Graphical AbstractFigure optionsDownload high-quality image (274 K)Download as PowerPoint slideHighlights
► Crystallization of an integral membrane protein directly from SDS with MPD cosolvent
► Externally bound SDS and cosolvent molecules identified at the protein surface
► The PagP hydrocarbon ruler pocket contains a single internally bound SDS molecule
► Identification of the lipid acyl chain entry route to the protein interior