Membrane association and isolation of the S-layer protein of Methanoculleus marisnigri

Abstract

Methanoculleus marisnigri is an irregularly shaped coccoid member of the methanogenic archaeobacteria. The cells possessed a hexagonally arranged, glycosylated S-layer as the sole wall component. The lattice spacing was approximately 13.5 nm. Plasmolysis in anaerobic medium with 20% sucrose did not separate the plasma membrane from the S-layer. The S-layer–membrane complex formed a tight but noncovalent association, was deformable, and was not a rigid structure. The 138-kDa glycoprotein was not solubilized by guanidine hydrochloride or urea, but it was solubilized in the detergent Triton X-100 at temperatures above 60 °C, and purified by phase separation at 75 °C of the detergent-soluble extract. The amino acid composition of the glycoprotein was similar to that reported for other S-layer proteins.Key words: methanogen, archaeobacteria (archaea), S-layer, glycoprotein, Triton X-100.