An autolysin ring associated with cell separation of Staphylococcus aureus

Abstract

atl is a newly discovered autolysin gene in Staphylococcus aureus. The gene product, ATL, is a unique, bifunctional protein that has an amidase domain and a glucosaminidase domain. It undergoes proteolytic processing to generate two extracellular peptidoglycan hydrolases, a 51-kDa endo-␤-N-acetylglucosaminidase and a 62-kDa N-acetylmuramyl-L-alanine amidase. It has been suggested that these enzymes are involved in the separation of daughter cells after cell division. We recently demonstrated that atl gene products are cell associated (unpublished data). The cell surface localization of the atl gene products was investigated by immunoelectron microscopy using anti-62-kDa N-acetylmuramyl-L-alanine amidase or anti-51-kDa endo-␤-Nacetylglucosaminidase immunoglobulin G. Protein A-gold particles reacting with the antigen-antibody complex were found to form a ring structure on the cell surface at the septal region for the next cell division site. Electron microscopic examination of an ultrathin section of the preembedded sample revealed preferential distribution of the gold particles at the presumptive sites for cell separation where the new septa had not been completed. The distribution of the gold particles on the surface of protoplast cells and the association of the gold particles with fibrous materials extending from the cells suggested that some atl gene products were associated with a cellular component extending from the cell membrane, such as lipoteichoic acid. The formation of a ring structure of atl gene products may be required for efficient partitioning of daughter cells after cell division.Peptidoglycan hydrolases are a group of enzymes which catalyze the turnover or degradation of peptidoglycan in bacteria. They include N-acetylglucosaminidases, N-acetylmuramidases, N-acetylmuramyl-L-alanine amidases (AMs), endopeptidases, and transglycosylases (for reviews, see references 1, 18, 22, 25, 26, and 34). These enzymes degrade peptidoglycan saccules, resulting in cell lysis. Therefore, the activities of these enzymes should be strictly regulated. Various physiological functions of these enzymes have been proposed, including their roles in cell separation, wall growth, wall turnover, muropeptide recycling, sporulation, formation of flagella, and transformation (for reviews, see references 22, 25, 26, and 34). Peptidoglycan hydrolases have also been implicated in autolysis induced by ␤-lactams or in bacterial pathogenesis (1, 2, 13-15, 19; for reviews, see references 22 and 26).Bacterial cell separation is a dynamic event in the cell cycle and requires cleavage of peptidoglycan connecting daughter cells. In many bacteria, correlation of a lack of peptidoglycan hydrolase(s) activity and a failure in cell separation has been reported (4,5,7,8,10,11,23,26,27,31,34,35). Recent studies have identified peptidoglycan hydrolases involved in cell separation in Listeria monocytogenes and in Lactococcus lactis (3, 36).We have previously described the identification of a 51-kDa endo-␤-N-acetylglucosaminidase (GL) and a 62...

The autolysin Ami contributes to the adhesion of Listeria monocytogenes to eukaryotic cells via its cell wall anchor

“…This receptor might be lipoteichoic acid (Fisher, 1994). This is consistent with immunoelectron microscopy data showing the association of Atl products with fibrous material extending from the staphylococcal cell membrane (Yamada et al, 1996). GW repeat domains are present in a growing family of surface proteins produced by Gram-positive bacteria, including L. monocytogenes InlB and Ami (Braun et al, 1997) and the staphylococcal autolysins Atl, AtlE and Aas (this study).…”

Molecular Characterization of an atl Null Mutant of Staphylococcus aureus

“…The 51 kDa GL and the 62 kDa AM were shown to disperse clusters of S. aureus without affecting cell viability (26). The atl gene products including 51 kDa GL and 62 kDa AM were found to form a ring structure on the cell surface at the septal region for the upcoming cell division site (30). These results suggested that the atl gene products are involved in cell separation.…”

Peptidoglycan architecture can specify division planes in Staphylococcus aureus

“…During this splitting and stretching, the rings observed by AFM are most likely to be remodelled into knobbles. Th e Y conformation is characteristic of eccentric attachment of daughter cells, as previously observed by phase contrast 1 and electron microscopy 19 , and allows the organisms to form irregular bunched clusters 1 rather than the more regular arrangements adopted by other genera that divide on orthogonal planes ( Fig. 5 ): cuboidal packets (for example, Sarcina ) or rectilinear grid arrangements (for example, Pediococcus ) 3 .…”

“…Th ese observations show that S. aureus are generally spherical, but adjacent pseudo-hemispherical cells have been observed 3,19 as the result of a recent division. Smooth and concentric ring-banded surface textures have been observed by electron microscopy of whole cells 3 and purifi ed sacculi 20 .…”