The perforate component of the regularly structured (RS) layer of Lampropedia hyalina

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Abstract
The regularly structured (RS) layer of Lampropedia hyalina was found to consist of two components; of these, the inner perforate layer was easily isolated from cell envelopes by dissolution of attached material by incubation in 2% sodium dodecyl sulfate at room temperature. The layer consisted of a 31.5-kilodalton polypeptide arranged in p6 symmetry so that, in negative stain, it appeared to be a sheet full of regularly arranged holes with a repeat frequency of 13 nm. The layer was stable in chelating and reducing agents, and in various detergents. Dissolution of the perforate layer occurred in boiling sodium dodecyl sulfate, 6 M guanidine–HCl, 8 M urea, 90% formic acid, and in buffers below pH 4 and above pH 11. In its dissociated state, the component polypeptide was sensitive to hydrolysis by endoproteinase glu-C, while the assembled polypeptide was not affected, suggesting that the acidic amino acid residues are hidden from the protease in the assembled state.