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Chapter 6 : Cell Wall Hydrolases

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Abstract:

Many bacterial species possess more than one enzyme that hydrolyzes the same bond, a fact that complicates the determination of their biological role(s). This redundancy also contributes to the common thought of assigning a basic role to lytic enzymes in the biology of bacteria. The activity of some pneumococcal murein hydrolases (MHs) appears to be constrained by the membrane lipoteichoic acid (LTA) at the posttranslational level. Cell wall hydrolases (CWHs) of show both substrate and bond specificities. The lytA gene encodes the major autolysin (amidase) and represents the first example of a bacterial autolytic gene that was cloned and expressed. LytB is most probably a glucosaminidase capable of degrading Ch-containing cell walls. All the pneumococcal CWHs described have been shown to possess an absolute requirement for the presence of Ch for activity. The cloning of lytA has facilitated the isolation of the genes encoding the cell wall lytic enzymes from pneumococcal bacteriophages based on sequence homologies. This global analysis led the authors to propose that pneumococcal cell wall lytic enzymes could be the result of the fusion of two independent functional domains. The construction of active chimeric proteins between lysins of phage and bacteria led to new enzymes exhibiting novel properties that were, as expected, a combination of those showed by the parental enzymes.

Citation: López R, García E, García P, García J. 2004. Cell Wall Hydrolases, p 75-88. In Tuomanen E, Mitchell T, Morrison D, Spratt B (ed), The Pneumococcus. ASM Press, Washington, DC. doi: 10.1128/9781555816537.ch6
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Image of FIGURE 1
FIGURE 1

Diagrammatic sketch of the cell wall of pneumococci, indicating the chemical bonds cleaved by different CWHs. The peptidoglycan chains and a repeat unit of TA are shown. Abbreviations: G and M, -acetylglucosamine and -acetylmuramic acid residues, respectively; Rib, ribitol-5-phosphate; GalNAc, -acetyl-D-galactosamine; AATGal, 2-acetamido- 4-amino,2,4,6-trideoxy-D-galactose; Glc, Dglucose; ChP, phosphorylcholine.

Citation: López R, García E, García P, García J. 2004. Cell Wall Hydrolases, p 75-88. In Tuomanen E, Mitchell T, Morrison D, Spratt B (ed), The Pneumococcus. ASM Press, Washington, DC. doi: 10.1128/9781555816537.ch6
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Image of FIGURE 2
FIGURE 2

Schematic representation of the structures of , , , and . (A) The genes are labeled as in references 32 and 65 above and below the arrows, respectively. Arrows indicate the direction of transcription of the ORFs. (B) The CWHs are drawn from the NH end to the COOH end. Black and dotted bars indicate the parts of the proteins corresponding to the signal peptide and the active center, respectively. Shaded rectangles correspond to the CBRs. aa, amino acids.

Citation: López R, García E, García P, García J. 2004. Cell Wall Hydrolases, p 75-88. In Tuomanen E, Mitchell T, Morrison D, Spratt B (ed), The Pneumococcus. ASM Press, Washington, DC. doi: 10.1128/9781555816537.ch6
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Image of FIGURE 3
FIGURE 3

Localization of GFP-LytB in the surface of . A culture of a mutant of the R6 strain received fusion protein (9.5 μg/ml) and was incubated for 1 min at 37°C. Pictures were taken with a Nikon Eclipse inverted microscope in phase-contrast (a) and using fluorescence (b). Bars, 4 μm. (Reprinted from the [8] with permission of the publisher.)

Citation: López R, García E, García P, García J. 2004. Cell Wall Hydrolases, p 75-88. In Tuomanen E, Mitchell T, Morrison D, Spratt B (ed), The Pneumococcus. ASM Press, Washington, DC. doi: 10.1128/9781555816537.ch6
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