Crystal structure of Escherichia coli-expressed Haloarcula marismortui bacteriorhodopsin I in the trimeric form

PLoS One. 2014 Dec 5;9(12):e112873. doi: 10.1371/journal.pone.0112873. eCollection 2014.


Bacteriorhodopsins are a large family of seven-helical transmembrane proteins that function as light-driven proton pumps. Here, we present the crystal structure of a new member of the family, Haloarcula marismortui bacteriorhodopsin I (HmBRI) D94N mutant, at the resolution of 2.5 Å. While the HmBRI retinal-binding pocket and proton donor site are similar to those of other archaeal proton pumps, its proton release region is extended and contains additional water molecules. The protein's fold is reinforced by three novel inter-helical hydrogen bonds, two of which result from double substitutions relative to Halobacterium salinarum bacteriorhodopsin and other similar proteins. Despite the expression in Escherichia coli and consequent absence of native lipids, the protein assembles as a trimer in crystals. The unique extended loop between the helices D and E of HmBRI makes contacts with the adjacent protomer and appears to stabilize the interface. Many lipidic hydrophobic tail groups are discernible in the membrane region, and their positions are similar to those of archaeal isoprenoid lipids in the crystals of other proton pumps, isolated from native or native-like sources. All these features might explain the HmBRI properties and establish the protein as a novel model for the microbial rhodopsin proton pumping studies.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacteriorhodopsins / chemistry*
  • Bacteriorhodopsins / genetics
  • Crystallography, X-Ray*
  • Escherichia coli / genetics
  • Haloarcula marismortui / chemistry*
  • Hydrogen Bonding
  • Hydrophobic and Hydrophilic Interactions
  • Protein Multimerization
  • Protein Structure, Secondary
  • Water / chemistry


  • Water
  • Bacteriorhodopsins

Associated data

  • PDB/4PXK

Grants and funding

The work was supported by the program "Chaires d'excellence" edition 2008 of ANR France and CEA(IBS) - HGF(FZJ) STC 5.1 specific agreement. Part of this work was supported by BMBF (PhoNa - Photonic Nanomaterials). The work was supported by RFBR (research projects 13-04-91320 and 12-04-31290) and the Russian state Program for enhancing the competitiveness of MIPT among the world's leading research and education centers of the Ministry of education and science. The work used the platforms of the Grenoble Instruct centre (ISBG; UMS 3518 CNRS-CEA-UJF-EMBL) with support from FRISBI (ANR-10-INSB-05-02) and GRAL (ANR-10-LABX-49-01) within the Grenoble Partnership for Structural Biology (PSB). VP is deeply thankful to Fondation Nanosciences for financial support. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.