title: Structure of the peptide network of pneumococcal peptidoglycan.
abstract: The peptide network of Streptococcus pneumoniae cell walls was solubilized using the pneumococcal autolytic amidase (N-acetylmuramoyl-L-alanine amidase, EC 3.5.1.28). The peptide material was fractionated into size classes by gel filtration followed by reverse-phase high-performance liquid chromatography which resolved the peptide population into over 40 fractions. About 40% of the lysines present participate in cross-links between stem peptides. The main components (3 monomers, 5 dimers, and 2 trimers), accounting for 77% of all the wall peptides, were purified. Their structures were determined using a combination of amino acid and end-group analysis, mass spectrometry, and gas-phase sequencing. Two different types of cross-links between stem peptides were found. In the most abundant type there is an alanylserine cross-bridge between the alanine in position 4 of the donor stem peptide and the lysine at position 3 of the acceptor peptide, as in type A3 peptidoglycan. In the second type of cross-link there is no intervening cross-bridge, as in the type A1 peptidoglycan of Gram-negative bacteria. The data indicate that pneumococcal peptidoglycan has a structural complexity comparable to that recently shown in some Gram-negative species.
mesh_terms: D002473:Cell Wall / Q000032:analysis*; D002851:Chromatography, High Pressure Liquid; D013058:Mass Spectrometry; D009238:N-Acetylmuramoyl-L-alanine Amidase / Q000378:metabolism; D010449:Peptide Mapping; D010457:Peptidoglycan / Q000032:analysis*; D011487:Protein Conformation; D012995:Solubility; D013296:Streptococcus pneumoniae / Q000648:ultrastructure*
chemical_list: D010457:Peptidoglycan; D009238:N-Acetylmuramoyl-L-alanine Amidase