A protein-sorting transpeptidase is an
enzyme
Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...
, such as the
sortase SrtA
of
Staphylococcus aureus
''Staphylococcus aureus'' is a Gram-positive spherically shaped bacterium, a member of the Bacillota, and is a usual member of the microbiota of the body, frequently found in the upper respiratory tract and on the skin. It is often posit ...
, that cleaves one or more target proteins produced by the same cell, as part of a specialized pathway of
protein targeting. The typical prokaryotic protein-sorting transpeptidase is characterized as a
protease
A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the form ...
, but does not simply hydrolyze a peptide bond. Instead, the larger, N-terminal portion of the cleaved polypeptide is transferred onto another molecule, such as a precursor of the
peptidoglycan
Peptidoglycan or murein is a unique large macromolecule, a polysaccharide, consisting of sugars and amino acids that forms a mesh-like peptidoglycan layer outside the plasma membrane, the rigid Cell wall#Bacterial_cell_walls, cell wall (murein sac ...
cell wall in
Gram-positive bacteria
In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall.
Gram-positive bact ...
.
The term
sortase is properly reserved for the set of
cysteine protease
Cysteine proteases, also known as thiol proteases, are hydrolase enzymes that degrade proteins. These proteases share a common catalytic mechanism that involves a nucleophilic cysteine thiol in a catalytic triad or dyad.
Discovered by Gopal ...
enzymes
sortase A
Sortase A (, ''SrtA'', ''SrtA protein'', ''SrtA sortase'') is an enzyme. This enzyme catalyses a cell wall
A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometime ...
,
sortase B Sortases are membrane anchored enzyme that sort these surface proteins onto the bacterial cell surface and anchor them to the peptidoglycan. There are different types of sortases and each catalyse the anchoring of different proteins to cell w ...
, and members of additional classes, all of which share homology. However, a growing number of additional protein sorting systems has been described in prokaryotes, involving sorting enzymes that lack any homology to sortase and that appear to have arisen separately by
convergent evolution
Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
. Although the sortases are the best described members of the protein-sorting transpeptidases, work on the analogous enzymes
archaeosortase,
,
and the PorU enzyme of type IX
secretion systems (T9SS)
has been accumulating.
References
{{reflist
Enzymes