Lipid modification gives rise to two distinct Haloferax volcanii S-layer glycoprotein populations

• Published in: Biochimica et biophysica acta Vol. 1828; no. 3; pp. 938 - 943
• Main Authors: Kandiba, Lina, Guan, Ziqiang, Eichler, Jerry
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-03-2013
• Subjects: Archaea; Archaeal Proteins - metabolism; Biophysics - methods; Chromatography, Liquid - methods; Edetic Acid - chemistry; Glycoproteins - chemistry; Glycosylation; Haloferax volcanii; Haloferax volcanii - metabolism; Hydrolysis; Lipid modification; Lipids - chemistry; Mass Spectrometry - methods; Membrane Glycoproteins - chemistry; Membrane protein; Protein Sorting Signals; Protein Structure, Tertiary; S-layer glycoprotein; Spectrometry, Mass, Electrospray Ionization - methods; Membrane protein; liquid chromatography-electrospray ionization mass spectrometry; Haloferax volcanii; Archaea; surface layer; methanol; S-layer glycoprotein; Lipid modification; trichloroacetic acid
• ISSN: 0005-2736; 0006-3002; 1879-2642
• DOI: 10.1016/j.bbamem.2012.11.023

The S-layer glycoprotein is the sole component of the protein shell surrounding Haloferax volcanii cells. The deduced amino acid sequence of the S-layer glycoprotein predicts the presence of a C-terminal membrane-spanning domain. However, several earlier observations, including the ability of EDTA to selectively solubilize the protein, are inconsistent with the presence of a trans-membrane sequence. In the present report, sequential solubilization of the S-layer glycoprotein by EDTA and then with detergent revealed the existence of two distinct populations of the S-layer glycoprotein. Whereas both S-layer glycoprotein populations underwent signal peptide cleavage and N-glycosylation, base hydrolysis followed by mass spectrometry revealed that a lipid, likely archaetidic acid, modified only the EDTA-solubilized version of the protein. These observations are consistent with the S-layer glycoprotein being initially synthesized as an integral membrane protein and subsequently undergoing a processing event in which the extracellular portion of the protein is separated from the membrane-spanning domain and transferred to a waiting lipid moiety.
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► The S-layer glycoprotein solely comprises the Haloferax volcanii surface layer ► Sequential EDTA and Triton X-100 treatment expose two distinct forms of the protein ► Both S-layer glycoprotein forms undergo signal peptide cleavage and N-glycosylation ► Only EDTA-solubilized S-layer glycoprotein is lipid-modified.