5/5/2021 0 Comments Yomi Pnp Download
MATERIALS AND METHODS Bacterial strains, plasmids, chemicals, and growth conditions.
Yomi Pnp Code A MurNAcThis pathway is encoded by a cluster of six genes, the first three of which are orthologs of Escherichia coli genes involved in N -acetylmuramic acid dissimilation and encode a MurNAc-6-phosphate etherase (MurQ), a MurNAc-6-phosphate-specific transcriptional regulator (MurR), and a MurNAc-specific phosphotransferase system (MurP).The first gene was shown to encode a cell wall-associated - N -acetylglucosaminidase (NagZ, formerly YbbD) that cleaves the terminal nonreducing N -acetylglucosamine of muropeptides and also accepts chromogenic or fluorogenic - N -acetylglucosaminides.The second gene was shown to encode an amidase (AmiE, formerly YbbE) that hydrolyzes the N -acetylmuramyl- l -Ala bond of MurNAc peptides but not this bond of muropeptides. Hence, AmiE requires NagZ, and in conjunction these enzymes liberate MurNAc by sequential hydrolysis of muropeptides. NagZ expression was induced at late exponential phase, and it was 6-fold higher in stationary phase. NagZ is noncovalently associated with lysozyme-degradable particulate material and can be released from it with salt. A nagZ mutant accumulates muropeptides in the spent medium and displays a lytic phenotype in late stationary phase. The evidence for a muropeptide catabolic pathway presented here is the first evidence for cell wall recovery in a Gram-positive organism, and this pathway is distinct from the cell wall recycling pathway of E. Bacteria are covered by an exoskeleton-like cell wall that protects the fragile membrane-enclosed cell, the protoplast, and withstands the high internal pressure of the cell, the turgor pressure ( 27 ). Despite its stabilizing function, the cell wall is not rigid and static but is highly flexible. It undergoes continuous resynthesis, remodeling, and degradation (turnover) in which a substantial amount of the murein (peptidoglycan), the stabilizing component of the bacterial cell wall, is released during logarithmic growth ( 5, 47 ). The Gram-positive model organism Bacillus subtilis was shown to release about 50 of its murein into the medium in one generation during growth ( 9, 42, 43 ). Gram-negative bacteria have an outer membrane that keeps most of the cell wall turnover products in the periplasmic space, but Gram-positive bacteria lack such a membrane barrier and therefore cannot retain their turnover products. ![]() The tripeptide is directly fed into the murein biosynthesis pathway by the muropeptide ligase Mpl, which transfers the tripeptide to UDP- N -acetylmuramic acid (MurNAc) ( 44 ). The tripeptide may also be degraded to its individual amino acids by - d -glutaminyl- m -DAP amidase (MpaA) and l -Ala- dl -Glu epimerase (YcjG) ( 49, 54 ). GlcNAc is converted to GlcNAc-6-phosphate by the GlcNAc kinase NagK ( 55 ), whereas anhMurNAc is first phosphorylated by the kinase AnmK, yielding MurNAc-6-phosphate, which is then converted to GlcNAc-6-phosphate by the etherase MurQ, which cleaves the lactyl ether substituent of MurNAc-6-phosphate ( 24, 35, 36, 56, 57 ). MurNAc is imported and phosphorylated by the MurP-specific phosphotransferase system, yielding cytoplasmic MurNAc-6-phosphate ( 13 ). ![]() Recently, the transcriptional regulator MurR was characterized, which, in conjunction with the catabolite activator protein (CAP), regulates the MurNAc etherase operon in E. Bs NagZ occurs in the late exponential and stationary growth phases mainly in a particulate form in the supernatant. It cleaves cell wall-derived muropeptides, thereby generating a substrate for a second enzyme of the pathway, Bs AmiE (formerly YbbE), an N -acetylmuramyl- l -alanine amidase. A nagZ deletion strain accumulates muropeptides in the medium, and the cells lyse at late stationary phase. We recognized that Bs Nag Z is identical to an enzyme that was characterized in the early 1970s and was proposed to be involved in recycling of the endogenous cell wall during growth ( 2, 45 ).
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