Repetitive Sequences in the Murein-Lipoprotein of the Cell Wall of Escherichia coli

Abstract

The amino-acid sequence of the murein-lipoprotein of the Escherichia coli cell wall is presented. This protein is covalently bound to a lipid component as well as to the murein (peptidoglycan, mucopeptide). The sequence is also highly repetitive. At the N-terminal portion, there are three adjacent almost identical sequences, indicating repeated duplication of a gene coding originally for 15 amino acids. The C-terminal part of the polypeptide chain is more variable but still shows striking homology when certain sequence gaps are introduced. The lipid is bound to the N-terminal serine of the dipeptide (Ser-Ser) that extends from the repetitive sequence. At the C-terminal end where the murein is bound, a tripeptide extends from the repetitive portion. Here there are several basic amino acids and the only aromatic amino acid in the lipoprotein. The sequence is Lys-Tyr-Arg-Lys. The linkage to the murein is formed between the epsilon-amino group of the C-terminal lysine and the carboxyl group of the optical L-center of meso-diaminopimelic acid. The polypeptide chain is composed of 57 amino acids and lacks glycine, proline, cysteine, phenylalanine, histidine, and tryptophan. 63% of the amino acids are hydrophilic, but because of the covalently linked lipid this structural membrane protein has very hydrophobic properties.