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Title: Open-cap Conformation of Intramembrane Protease GlpG

Abstract

The active sites of intramembrane proteases are positioned in the lipid bilayer to facilitate peptide bond hydrolysis in the membrane. Previous crystallographic analysis of Escherichia coli GlpG, an intramembrane protease of the rhomboid family, has revealed an internal and hydrophilic active site in an apparently closed conformation. Here we describe the crystal structure of GlpG in a more open conformation, where the capping loop L5 has been lifted, exposing the previously buried and catalytically essential Ser-201 to outside aqueous solution. A water molecule now moves into the putative oxyanion hole that is constituted of a main-chain amide (Ser-201) and two conserved side chains (His-150 and Asn-154). The loop movement also destabilizes a hydrophobic side chain (Phe-245) previously buried between transmembrane helices S2 and S5 and creates a side portal from the lipid to protease active site. These results provide insights into the conformational plasticity of GlpG to accommodate substrate binding and catalysis and into the chirality of the reaction intermediate.

Authors:
;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930296
Report Number(s):
BNL-81001-2008-JA
TRN: US200822%%1453
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Proceedings of the National Academy of Sciences of the USA; Journal Volume: 104; Journal Issue: 7
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; AMIDES; AQUEOUS SOLUTIONS; CATALYSIS; CHIRALITY; CRYSTAL STRUCTURE; ESCHERICHIA COLI; HOLES; HYDROLYSIS; LIPIDS; MOLECULES; PEPTIDES; PLASTICITY; REACTION INTERMEDIATES; SUBSTRATES; WATER; national synchrotron light source

Citation Formats

Wang,Y., and Ha, Y. Open-cap Conformation of Intramembrane Protease GlpG. United States: N. p., 2007. Web. doi:10.1073/pnas.0611080104.
Wang,Y., & Ha, Y. Open-cap Conformation of Intramembrane Protease GlpG. United States. doi:10.1073/pnas.0611080104.
Wang,Y., and Ha, Y. Mon . "Open-cap Conformation of Intramembrane Protease GlpG". United States. doi:10.1073/pnas.0611080104.
@article{osti_930296,
title = {Open-cap Conformation of Intramembrane Protease GlpG},
author = {Wang,Y. and Ha, Y.},
abstractNote = {The active sites of intramembrane proteases are positioned in the lipid bilayer to facilitate peptide bond hydrolysis in the membrane. Previous crystallographic analysis of Escherichia coli GlpG, an intramembrane protease of the rhomboid family, has revealed an internal and hydrophilic active site in an apparently closed conformation. Here we describe the crystal structure of GlpG in a more open conformation, where the capping loop L5 has been lifted, exposing the previously buried and catalytically essential Ser-201 to outside aqueous solution. A water molecule now moves into the putative oxyanion hole that is constituted of a main-chain amide (Ser-201) and two conserved side chains (His-150 and Asn-154). The loop movement also destabilizes a hydrophobic side chain (Phe-245) previously buried between transmembrane helices S2 and S5 and creates a side portal from the lipid to protease active site. These results provide insights into the conformational plasticity of GlpG to accommodate substrate binding and catalysis and into the chirality of the reaction intermediate.},
doi = {10.1073/pnas.0611080104},
journal = {Proceedings of the National Academy of Sciences of the USA},
number = 7,
volume = 104,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • Escherichia coli GlpG is an integral membrane protein that belongs to the widespread rhomboid protease family. Rhomboid proteases, like site-2 protease (S2P) and {gamma}-secretase, are unique in that they cleave the transmembrane domain of other membrane proteins. Here we describe the 2.1 {angstrom} resolution crystal structure of the GlpG core domain. This structure contains six transmembrane segments. Residues previously shown to be involved in catalysis, including a Ser-His dyad, and several water molecules are found at the protein interior at a depth below the membrane surface. This putative active site is accessible by substrate through a large 'V-shaped' opening thatmore » faces laterally towards the lipid, but is blocked by a half-submerged loop structure. These observations indicate that, in intramembrane proteolysis, the scission of peptide bonds takes place within the hydrophobic environment of the membrane bilayer. The crystal structure also suggests a gating mechanism for GlpG that controls substrate access to its hydrophilic active site.« less
  • Intramembrane proteolysis regulates diverse biological processes. Cleavage of substrate peptide bonds within the membrane bilayer is catalyzed by integral membrane proteases. Here we report the crystal structure of the transmembrane core domain of GlpG, a rhomboid-family intramembrane serine protease from Escherichia coli. The protein contains six transmembrane helices, with the catalytic Ser201 located at the N terminus of helix {alpha}4 approximately 10 Angstroms below the membrane surface. Access to water molecules is provided by a central cavity that opens to the extracellular region and converges on Ser201. One of the two GlpG molecules in the asymmetric unit has an openmore » conformation at the active site, with the transmembrane helix {alpha}5 bent away from the rest of the molecule. Structural analysis suggests that substrate entry to the active site is probably gated by the movement of helix {alpha}5.« less
  • Intramembrane proteases are important enzymes in biology. The recently solved crystal structures of rhomboid protease GlpG have provided useful insights into the mechanism of these membrane proteins. Besides revealing an internal water-filled cavity that harbored the Ser-His catalytic dyad, the crystal structure identified a novel structural domain (L1 loop) that lies on the side of the transmembrane helices. Here, using site-directed mutagenesis, we confirmed that the L1 loop is partially embedded in the membrane, and showed that alanine substitution of a highly preferred tryptophan (Trp136) at the distal tip of the L1 loop near the lipid:water interface reduced GlpG proteolyticmore » activity. Crystallographic analysis showed that W136A mutation did not modify the structure of the protease. Instead, the polarity for a small and lipid-exposed protein surface at the site of the mutation has changed. The crystal structure, now refined at 1.7 Angstroms resolution, also clearly defined a 20-Angstroms-wide hydrophobic belt around the protease, which likely corresponded to the thickness of the compressed membrane bilayer around the protein. This improved structural model predicts that all critical elements of the catalysis, including the catalytic serine and the L5 cap, need to be positioned within a few angstroms of the membrane surface, and may explain why the protease activity is sensitive to changes in the protein:lipid interaction. Based on these findings, we propose a model where the end of the substrate transmembrane helix first partitions out of the hydrophobic core region of the membrane before it bends into the protease active site for cleavage.« less
  • Regulated intramembrane proteolysis by members of the site-2 protease (S2P) family is an important signaling mechanism conserved from bacteria to humans. Here we report the crystal structure of the transmembrane core domain of an S2P metalloprotease from Methanocaldococcus jannaschii. The protease consists of six transmembrane segments, with the catalytic zinc atom coordinated by two histidine residues and one aspartate residue {approx}14 angstroms into the lipid membrane surface. The protease exhibits two distinct conformations in the crystals. In the closed conformation, the active site is surrounded by transmembrane helices and is impermeable to substrate peptide; water molecules gain access to zincmore » through a polar, central channel that opens to the cytosolic side. In the open conformation, transmembrane helices {alpha}1 and {alpha}6 separate from each other by 10 to 12 angstroms, exposing the active site to substrate entry. The structure reveals how zinc embedded in an integral membrane protein can catalyze peptide cleavage.« less
  • Intramembrane aspartyl proteases (IAPs) comprise one of four families of integral membrane proteases that hydrolyze substrates within the hydrophobic lipid bilayer. IAPs include signal peptide peptidase, which processes remnant signal peptides from nascent polypeptides in the endoplasmic reticulum, and presenilin, the catalytic component of the γ-secretase complex that processes Notch and amyloid precursor protein. Despite their broad biomedical reach, basic structure-function relationships of IAPs remain active areas of research. Characterization of membrane-bound proteins is notoriously challenging due to their inherently hydrophobic character. For IAPs, oligomerization state in solution is one outstanding question, with previous proposals for monomer, dimer, tetramer, andmore » octamer. Here we used small angle neutron scattering (SANS) to characterize n-dodecyl-β-D-maltopyranoside (DDM) detergent solutions containing and absent a microbial IAP ortholog. A unique feature of SANS is the ability to modulate the solvent composition to mask all but the enzyme of interest. The signal from the IAP was enhanced by deuteration and, uniquely, scattering from DDM and buffers were matched by the use of both tail-deuterated DDM and D 2O. The radius of gyration calculated for IAP and the corresponding ab initio consensus model are consistent with a monomer. The model is slightly smaller than the crystallographic IAP monomer, suggesting a more compact protein in solution compared with the crystal lattice. In conclusion, our study provides direct insight into the oligomeric state of purified IAP in surfactant solution, and demonstrates the utility of fully contrast-matching the detergent in SANS to characterize other intramembrane proteases and their membrane-bound substrates.« less