Studies on the cell wall of Spirillum serpens. II. Chemical characterization of the outer structured layer

Abstract

The outer cell-wall layer of Spirillum serpens VHA, composed of a hexagonal array of macromolecules, was dissociated from 'cleaned' cell-wall fragments with 1.5 M guanidine hydrochloride, pH 7.0. The soluble material contained 98% protein, 2% carbohydrate, and no ethanolamine, phosphate, RNA, or DNA. Evidence for the homogeneity of the isolated cell-wall protein was obtained by sedimentation velocity, polyacrylamide disc gel electrophoresis, molecular sieve chromatography on Sephadex G-200, and sucrose density gradients. The protein was acidic and had a minimum molecular weight of about 48 000 daltons calculated from the amino acid analysis. A molecular weight of between 125 000 and 150 000 daltons was obtained for the protein by polyacrylamide disc-gel electrophoresis, sucrose density gradients, and molecular sieve chromatography. The sedimentation rate of the protein was considerably less in 1.5 M guanidine hydrochloride, pH 7.0, than in its absence although the protein remained homogenous under both conditions. Self-assembly of the purified protein into its original hexagonal layer on a template of wall fragments from which the protein had been removed previously was obtained when the mixture was incubated in the presence, but not in the absence of Ca2+. It seems likely that the particles (hexagons) seen on the surface of the cell are an assembly of trimers.