M protein is a virulence factor

Virulence factor

Virulence factors are molecules expressed and secreted by pathogens that enable them to achieve the following:* colonization of a niche in the host...

 that can be produced by certain species of Streptococcus

Streptococcus

Streptococcus is a genus of spherical Gram-positive bacteria belonging to the phylum Firmicutes and the lactic acid bacteria group. Cellular division occurs along a single axis in these bacteria, and thus they grow in chains or pairs, hence the name — from Greek στρεπτος streptos, meaning...

.

Viruses, parasites and bacteria

Zinc dependent phospholipase C

Zinc-dependent prokaryotic phospholipases C is a family of bacterial phospholipases C, some of which are also known as alpha toxins.Bacillus cereus contains a monomeric phospholipase C of 245 amino-acid residues. Although PLC prefers to acton phosphatidylcholine, it also shows weak catalytic...

 are covered in protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 and sugar

Sugar

Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...

 molecule

Molecule

A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

s that help them gain entry into a host by counteracting the host's defences. One such molecule is the M protein produced by certain streptococcal bacteria. M protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s embody a motif that is now known to be shared by many Gram-positive

Gram-positive

Gram-positive bacteria are those that are stained dark blue or violet by Gram staining. This is in contrast to Gram-negative bacteria, which cannot retain the crystal violet stain, instead taking up the counterstain and appearing red or pink...

 bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

l surface proteins. The motif

Sequence motif

In genetics, a sequence motif is a nucleotide or amino-acid sequence pattern that is widespread and has, or is conjectured to have, a biological significance...

 includes a conserved

Conserved sequence

In biology, conserved sequences are similar or identical sequences that occur within nucleic acid sequences , protein sequences, protein structures or polymeric carbohydrates across species or within different molecules produced by the same organism...

 hexapeptide, which precedes a hydrophobic C-terminal membrane

Cell membrane

The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

 anchor, which itself precedes a cluster of basic

Base (chemistry)

For the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...

 residues

Residue (chemistry)

In chemistry, residue is the material remaining after a distillation or an evaporation, or to a portion of a larger molecule, such as a methyl group. It may also refer to the undesired byproducts of a reaction....

.

M protein is strongly anti-phagocytic and is a major virulence factor. It binds to serum factor H

Factor H

Factor H is a member of the regulators of complement activation family and is a complement control protein. It is a large , soluble glycoprotein that circulates in human plasma...

, destroying C3 convertase and preventing opsonization by C3b

C3b

C3b is the larger of two elements formed by the cleavage of complement component 3. C3b covalently bonds to microbial cell surfaces within an organism's body. This leads to the production of surface-bound C3 convertase and thus more C3b components. Bound C3b also aids in opsonization of the microbe...

. However plasma B cells can generate antibodies against M protein which will help in opsonization and further off destruction of the microorganism by the macrophages and neutrophilis. Cross-reactivity

Cross-reactivity

Cross-reactivity is the reaction between an antibody and an antigen that differs from the immunogen. It is sometimes also referred to as crossimmunity or cross-protective immunity...

 of anti-M protein antibodies with heart muscle is the basis for rheumatic fever

Rheumatic fever

Rheumatic fever is an inflammatory disease that occurs following a Streptococcus pyogenes infection, such as strep throat or scarlet fever. Believed to be caused by antibody cross-reactivity that can involve the heart, joints, skin, and brain, the illness typically develops two to three weeks after...

.

It was originally identified by Rebecca Lancefield

Rebecca Lancefield

Rebecca Craighill Lancefield was a prominent American microbiologist. She joined the Rockefeller Institute for Medical Research in New York in 1918, and was associated with that institute throughout her long and outstanding career. Her bibliography comprises more than 50 publications published...

, who also formulated the Lancefield classification system for Streptococcal bacteria. Bacteria like S. pyogenes which possess M protein are classified in group A of the Lancefield system.