molecular biology Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and physi ...

, zinc-dependent phospholipases C is a family of bacterial phospholipases C

enzymes 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 ...

, some of which are also known as alpha toxins. ''

Bacillus cereus ''Bacillus cereus'' is a Gram-positive rod-shaped bacterium commonly found in soil, food, and marine sponges. The specific name, ''cereus'', meaning "waxy" in Latin, refers to the appearance of colonies grown on blood agar. Some strains are ha ...

'' contains a monomeric phospholipase C (PLC) of 245 amino-acid residues. Although PLC prefers to act on

phosphatidylcholine Phosphatidylcholines (PC) are a class of phospholipids that incorporate choline as a headgroup. They are a major component of biological membranes and can be easily obtained from a variety of readily available sources, such as egg yolk or soyb ...

, it also shows weak catalytic activity with

sphingomyelin Sphingomyelin (SPH, ˌsfɪŋɡoˈmaɪəlɪn) is a type of sphingolipid found in animal cell membranes, especially in the membranous myelin sheath that surrounds some nerve cell axons. It usually consists of phosphocholine and ceramide, or a ethano ...

and

phosphatidylinositol Phosphatidylinositol (or Inositol Phospholipid) consists of a family of lipids as illustrated on the right, where red is x, blue is y, and black is z, in the context of independent variation, a class of the phosphatidylglycerides. In such molecul ...

. Sequence studies have shown the protein to be similar both to alpha toxin from ''

Clostridium perfringens ''Clostridium perfringens'' (formerly known as ''C. welchii'', or ''Bacillus welchii'') is a Gram-positive, rod-shaped, anaerobic, spore-forming pathogenic bacterium of the genus '' Clostridium''. ''C. perfringens'' is ever-present in nature an ...

'' and '' Clostridium bifermentans'', a phospholipase C involved in haemolysis and cell rupture, and to

lecithinase Lecithinase is a type of phospholipase that acts upon lecithin. It can be produced by ''Clostridium perfringens'', ''Staphylococcus aureus'', ''Pseudomonas aeruginosa'' or ''Listeria monocytogenes''. ''C. perfringens'' alpha toxin (lecithinase) c ...

from ''

Listeria monocytogenes ''Listeria monocytogenes'' is the species of pathogenic bacteria that causes the infection listeriosis. It is a facultative anaerobic bacterium, capable of surviving in the presence or absence of oxygen. It can grow and reproduce inside the host' ...

'', which aids cell-to-cell spread by breaking down the 2-membrane vacuoles that surround the bacterium during transfer. Each of these proteins is a zinc-dependent enzyme, binding 3 zinc ions per molecule. The enzymes catalyse the conversion of phosphatidylcholine and water to 1,2-diacylglycerol and choline phosphate. In ''Bacillus cereus'', there are nine residues known to be involved in binding the zinc ions: 5 His, 2 Asp, 1 Glu and 1 Trp. These residues are all conserved in the ''Clostridium'' alpha-toxin. Some examples of this enzyme contain a C-terminal sequence extension that contains a PLAT domain which is thought to be involved in membrane localisation.

References

EC 3.1.4 Protein domains Peripheral membrane proteins Zinc proteins {{membrane-protein-stub