Primary structure of cyanelle peptidoglycan of Cyanophora paradoxa: a prokaryotic cell wall as part of an organelle envelope

Abstract

The peptidoglycan layer surrounding the photosynthetic organelles (cyanelles) of the protist Cyanophora paradoxa is thought to be a relic of their cyanobacterial ancestors. The separation of muropeptides by gel filtration and reverse-phase high-performance liquid chromatography revealed four different muropeptide monomers. A number of muropeptides were identical in retention behavior to muropeptides of Escherichia coli, while others had remarkably long retention times with respect to their sizes, as indicated by gel filtration. Molecular mass determination by plasma desorption and matrix-assisted laser desorption ionization mass spectrometry showed that these unusual muropeptides had molecular masses greater by 112 Da or a multiple thereof than those of ones common to both species. Fast atom bombardment-tandem mass spectrometry of these reduced muropeptide monomers allowed the localization of the modification to D-glutamic acid. Highresolution fast atom bombardment-mass spectrometry and amino acid analysis revealed N-acetylputrescine to be the substituent (E. Pittenauer, E. R. Among eukaryotes, peptidoglycan is found only in cyanellecontaining organisms. These consist of about 12 different species and have been grouped under the denomination glaucocystophytes (29). Recently, this has been corroborated by 18S rRNA-derived phylogenetic analysis (5). Cyanophora paradoxa is the only member of this group which can be grown easily; therefore, it is the best investigated one. The round cyanelles of this obligatorily photoautotrophic protist were originally regarded as endosymbiotic cyanobacteria for morphological reasons, such as thylakoid structure (13), carboxysomes (31), and a lysozyme-sensitive peptidoglycan sacculus (37). With the onset of molecular biological investigations of C. paradoxa (18,32), it became clear that the cyanelle genome is smaller than the genomes of unicellular free-living cyanobacteria by a factor of about 25. Thus, cyanelles in fact represent the plastids of C. paradoxa, having retained the peptidoglycan layer which is crucial for division, as indicated by the inhibitory effects of ␤-lactam antibiotics (4, 29). The peptidoglycan layer is located between the organelle membrane and an outer membrane of unknown origin and has a thickness of about 7 nm (30).Investigations of cyanelle peptidoglycan synthesis and degradation have shown that cyanelles apparently harbor a complete set of enzymes involved in these processes. Seven penicillin-binding proteins ranging from 110 to 35 kDa have been identified in the cyanelle envelope by labelling with a radioactive derivative of ampicillin (4). Indirect evidence has been obtained for periplasmic localization of DD-and LD-carboxypeptidases and DD-endopeptidase, enzymes capable of hydrolyzing defined bonds in peptidoglycan (36). The biosynthesis of the UDP-N-acetylmuramyl pentapeptide precursor of peptidoglycan has been shown to occur in the cyanelle stroma (36). The cyanelle genome (135.6 kb) of one of the two known isolates of C. paradoxa, strain LB555-UT...

Peptidoglycan structure of Salmonella typhimurium growing within cultured mammalian cells

“…These analyses provide substantial structural information derived from muropeptide-composition data. The sensitivity of this type of analysis has permitted the identification and qualification of peptidoglycan components down to the low level of 1-10 ng (Allmaier and Schimd, 1993), with successful results in the elucidation of peptidoglycan contained in the photosynthetic organelles (cyanelles) of the algae Cyanophora paradoxa (Pfanzagl et al, 1996). Nevertheless, no study has previously been performed that applied similar analytical procedures to characterize the peptidoglycan structure of intracellular bacteria.…”

Monophyly of Archaeplastida supergroup and relationships among its lineages in the light of phylogenetic and phylogenomic studies. Are we close to a consensus?

“…Glaucophytes are usually considered to be the earliest branch of the Archaeplastida because their plastids retain more ancestral features typical of cyanobacteria than are present in red algae or green plants; for example, peptidoglycan and carboxysomes [14,15]. Other characteristics that distinguish the Glaucophyta from the Rhodophyta and Viridiplantae include (i) the presence of a cyanobacterial-like fructose-1,6-bisphosphate aldolase, which was replaced by a duplicated cytosolic copy in the case of the other Archaeplastida lineages [144], (ii) lack of triple-helix chlorophyll-binding, light harvesting antenna complexes [145,146] and (iii) lack of plastidial phosphatetranslocator [20].…”

“…Glaucophyte plastids (called cyanelles) retain more cyanobacterial characteristics than do red alga and green plant plastids. The most remarkable is the presence of peptidoglycan, a typical component of bacterial cell walls located between the inner and outer membrane [14], as well as carboxysomes with enzymes involved in carbon fixation [15]. In addition, glaucophytes and rhodophytes still possess phycobilisomes, typical cyanobacterial photosystem II light-harvesting antennae [16].…”

The Glaucophyta: the blue-green plants in a nutshell

“…The peptidoglycan of the glaucophyte plastid PGW [120] is characterized by the presence of N-acetylputrescine as the chemical substituent in half of the 1-carboxyl groups of the glutamic acid residues of the peptide chains [121,122]. Experimental studies have demonstrated that the biosynthesis of the peptidoglycan precursor (UDP-N-acetylmuramylpentapeptide) occurs in the glaucophyte plastid stroma, and that the assembly of the polymer network occurs in the periplasmic space [60,123].…”