Autolysin
Template:Short description Autolysins are endogenous lytic enzymes that break down the peptidoglycan components of biological cells which enables the separation of daughter cells following cell division.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite book</ref><ref name=":0">Template:Cite journal</ref><ref>Template:Cite journal</ref> They are involved in cell growth, cell wall metabolism, cell division and separation, as well as peptidoglycan turnover and have similar functions to lysozymes.<ref name=":1">Template:Cite journal</ref>
Autolysin is formed from the precursor gene, Atl. Amidases (EC 3.5.1.28), gametolysin (EC 3.4.24.38), and glucosaminidase are considered as types of autolysins.<ref name=":0" /><ref name=":1" />
Function and mechanismsEdit
Autolysins exist in all bacteria containing peptidoglycan and are potentially considered as lethal enzymes when uncontrolled.<ref>Template:Cite journal</ref> They target the glycosidic bonds as well as the cross-linked peptides of the peptidoglycan matrix.<ref name="pmid24692449">Template:Cite journal</ref> The peptidoglycan matrix functions for cell wall stability to protect from turgor changes and carries out function for immunological defense.<ref>Template:Cite journal</ref><ref>Template:Cite book</ref> These enzymes break down the peptidoglycan matrix in small sections to allow for peptidoglycan biosynthesis.<ref name=":0" /> Autolysins breaks down old peptidoglycan which allows for the formation of newer peptidoglycan for cell growth and elongation. This is called cell wall turnover.<ref name=":1" /> Autolysins do this by hydrolyzing the β-(1,4) glycosidic bond of the peptidoglycan cell wall and the linkage between N-acetylmuramoyl residues and L-amino acid residues of certain cell-wall glycopeptides.<ref name=":0" /> This enzyme catalyses the following chemical reaction:
- Cleavage of the proline- and hydroxyproline-rich proteins of the Chlamydomonas cell wall; also cleaves azocasein, gelatin and Leu-Trp-Met-Arg-Phe-Ala
This glycoprotein is present in Chlamydomonas reinhardtii gametes.
Gram-positive bacteria regulate autolysins with teichoic acid molecules attached to the tetrapeptide of the peptidoglycan matrix.
The antibiotics complestatin and corbomycin prevent autolysin from remodeling the cell wall by binding to peptidoglycan, therefore stopping bacterial growth.<ref name="CulpWaglechner2020">Template:Cite journal</ref> The amide linkages between stem peptide and lactyl moiety of muramoyl residue are cleaved by N-acetylmuramoyl-l-alanine amidases and partakes in cell separation and the dissociation of the cell septum.<ref name=":0" /> There are 5 types of autolysins that contribute to cell separation of daughter cells, LytC, LytD, LytE, and LytF.<ref name=":1" />
In a study conducted with mice, those that were immunized with autolysin were able to survive longer than the infected mice. This study was able to support as evidence autolysin's contribution in virulence and potential for vaccine antigen.<ref name=":3">Template:Cite journal</ref>
Lysis of mother cellEdit
Template:Infobox enzyme LytC and CwlC are two amidases from the LytC family that hydrolyze the peptidoglycan of the mother cell wall to allow for the release of the mature endospore. CwlC is directly found in the mother cell wall.<ref name=":1" />
MotilityEdit
Expression of lytC, lytD, and lytF genes together leads to flagellar motility and is controlled by the activity of the chemotaxis sigma factor, σD. The activity of this sigma factor peaks at the start of the stationary phase.<ref name=":1" />
Potential lethalityEdit
Autolysins are naturally produced by peptidoglycan containing bacteria, but excessive amounts will degrade the peptidoglycan matrix and cause the cell to burst due to osmotic pressure. Previous studies have found that the byproducts of autolysin during cell wall breakdown are highly immunogenic.<ref name=":3" /> When observed in the bacteria, Bacillus subtilis, there were potentially lethal amounts of autolysin found in the cell walls.<ref name=":1" /> In Streptococcus pneumoniae it was found that N-acetylmuramoyl-l-alanine amidase, a cell wall autolysin, could assist in pathogenesis due to its ability to break down the wall or lyse a portion of the invading pneumococci and release potentially lethal toxins into the cell. Researchers studied the function, structure, and cloning ability through Escherichia coli and also determined its nucleotide sequence.<ref name=":3" />
FamiliesEdit
LytC amidase familyEdit
LytCEdit
LytC as well as LytD are considered as two major autolysins that contribute to vegetative cell wall growth and account for 95% of the autolytic activity in B. subtilis. LytC is found in the cell wall. LytB, a non-autolysin, was found to enhance LytC activity.<ref name=":1" /> LytC and LytA interact and function together for lysis and cell death.<ref>Template:Cite journal</ref>Template:Infobox enzyme
CwlCEdit
CwlC is found in the mother cell wall and functions for the lysis of the mother cell wall.<ref name=":1" /> CwlC does not have a signal sequence but participates in late sporulation and is present in the cell wall.<ref name=":2">Template:Cite journal</ref><ref>Template:Cite journal</ref> It was found in B. subtilis that CwlC is able to hydrolyze both vegetative cell walls and spore peptidoglycan.<ref name=":2" />
LytD glucosaminidase familyEdit
This family of autolysin consist of only LytD itself. LytD functions for vegetative growth. Autolytic activity is found within the C-terminal region with catalytic domain homologous to the glucosaminidase domain. LytD is found in the cell wall. LytD activity was studied in B. subtilis and glucosaminidase activity was found in mature glycan strands due to the presence of MurNAc at the nonreducing ends.<ref name=":1" />
See alsoEdit
ReferencesEdit
External linksEdit
Template:Metalloendopeptidases Template:Enzymes Template:Portal bar