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Archaea. 2012; 2012: 873589.
Published online May 15, 2012. doi:  10.1155/2012/873589
PMCID: PMC3361143
Identification of the Major Expressed S-Layer and Cell Surface-Layer-Related Proteins in the Model Methanogenic Archaea: Methanosarcina barkeri Fusaro and Methanosarcina acetivorans C2A
Lars Rohlin, 1 ,2 Deborah R. Leon, 3 ,4 Unmi Kim, 1 ,5 Joseph A. Loo, 2 ,3 ,6 Rachel R. Ogorzalek Loo, 2 ,6 * and Robert P. Gunsalus 1 ,2 *
1Department of Microbiology, Immunology, and Molecular Genetics, University of California, Los Angeles, CA 90095, USA
2UCLA-DOE Institute for Genomics and Proteomics, University of California, Los Angeles, CA 90095, USA
3Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, USA
4Mass Spectrometry Resource, Boston University School of Medicine, 670 Albany Street, Rm 511, Boston, MA 02118, USA
5OPX Biotechnologies, Inc. Research Division, 2425 55th Street, Boulder, CO 80301, USA
6Department of Biological Chemistry, University of California, Los Angeles, CA 90095, USA
*Rachel R. Ogorzalek Loo: rloo/at/mednet.ucla.edu and
*Robert P. Gunsalus: robg/at/microbio.ucla.edu
Academic Editor: Jerry Eichler
Received December 28, 2011; Accepted February 2, 2012.
Abstract
Many archaeal cell envelopes contain a protein coat or sheath composed of one or more surface exposed proteins. These surface layer (S-layer) proteins contribute structural integrity and protect the lipid membrane from environmental challenges. To explore the species diversity of these layers in the Methanosarcinaceae, the major S-layer protein in Methanosarcina barkeri strain Fusaro was identified using proteomics. The Mbar_A1758 gene product was present in multiple forms with apparent sizes of 130, 120, and 100 kDa, consistent with post-translational modifications including signal peptide excision and protein glycosylation. A protein with features related to the surface layer proteins found in Methanosarcina acetivorans C2A and Methanosarcina mazei Goel was identified in the M. barkeri genome. These data reveal a distinct conserved protein signature with features and implied cell surface architecture in the Methanosarcinaceae that is absent in other archaea. Paralogous gene expression patterns in two Methanosarcina species revealed abundant expression of a single S-layer paralog in each strain. Respective promoter elements were identified and shown to be conserved in mRNA coding and upstream untranslated regions. Prior M. acetivorans genome annotations assigned S-layer or surface layer associated roles of eighty genes: however, of 68 examined none was significantly expressed relative to the experimentally determined S-layer gene.
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