Maurer's clefts are membranous structures seen in the

red blood cell Red blood cells (RBCs), referred to as erythrocytes (, with -''cyte'' translated as 'cell' in modern usage) in academia and medical publishing, also known as red cells, erythroid cells, and rarely haematids, are the most common type of blood cel ...

during infection with ''

Plasmodium falciparum ''Plasmodium falciparum'' is a Unicellular organism, unicellular protozoan parasite of humans and is the deadliest species of ''Plasmodium'' that causes malaria in humans. The parasite is transmitted through the bite of a female ''Anopheles'' mos ...

''. The function and contents of Maurer's clefts are not completely known; however, they appear to play a role in trafficking of ''Plasmodium falciparum'' erythrocyte membrane protein 1 (PfEMP1) and other adhesins to the red blood cell surface.

Description

RBC with P falciparum Maurers clefts highlighted

Maurer's clefts appear in the

cytosol The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells ( intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...

of red blood cells 2 to 4 hours after invasion by ''P. falciparum''. They originally appear as small membrane-bound vacuoles, likely originating from the parasitophorous vacuole membrane. However, as the parasite ages Maurer's clefts expand to form single flattened

cisterna A cisterna (: cisternae) is a flattened membrane vesicle found in the endoplasmic reticulum and Golgi apparatus. Cisternae are an integral part of the packaging and modification processes of proteins occurring in the Golgi. Function Proteins begi ...

e, 500-nanometers wide. In parasite strains lacking the protein REX1, Maurer's clefts instead appear as stacks of

e, similar to stacks of

Golgi bodies The Golgi apparatus (), also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic Cell (biology), cells. Part of the endomembrane system in the cytoplasm, it protein targeting, packages proteins ...

. For the first half of the parasite life cycle, Maurer's clefts are highly mobile in the host cytoplasm. However, as parasites transition to the

trophozoite A trophozoite (G. ''trope'', nourishment + ''zoon'', animal) is the activated, feeding stage in the life cycle of certain protozoa such as malaria-causing ''Plasmodium falciparum'' and those of the ''Giardia'' group. The complementary form of the t ...

stage Maurer's clefts become fixed in place. This fixation coincides with PfEMP1 appearing on the host cell surface. The structures tethering Maurer's clefts to the host cell membrane are visible by

transmission electron microscopy Transmission electron microscopy (TEM) is a microscopy technique in which a beam of electrons is transmitted through a specimen to form an image. The specimen is most often an ultrathin section less than 100 nm thick or a suspension on a g ...

as cylindrical structures 200–300 nanometers long and 30 nanometers wide. The structure of these tethers is poorly defined, but they appear to contain the parasite protein MAHRP2 and/or involve host

actin Actin is a family of globular multi-functional proteins that form microfilaments in the cytoskeleton, and the thin filaments in muscle fibrils. It is found in essentially all eukaryotic cells, where it may be present at a concentration of ...

Function

Maurer's clefts are thought function as sorting centers, through which parasite proteins are trafficked on their way to the red blood cell surface. The most important of these are parasite proteins involved in binding of infected red blood cells to the host blood vessels, such as PfEMP1s, repetitive interspersed family proteins ( RIFINs), and subtelomeric variant

open reading frame In molecular biology, reading frames are defined as spans of DNA sequence between the start and stop codons. Usually, this is considered within a studied region of a prokaryotic DNA sequence, where only one of the six possible reading frames ...

proteins ( STEVORs), all of which localize to the Maurer's clefts on their way to the red blood cell surface. A number of other parasite proteins involved in modifying the host cell also localize to the Maurer's clefts such as PfMC-2TMs, FIKK kinases, as well as some members of the ''Plasmodium'' helical interspersed subtelomeric ( PHIST) family of parasite proteins.

History

Georg Maurer first described the structures now known as Maurer's clefts in 1902, when he described

methylene blue Methylthioninium chloride, commonly called methylene blue, is a salt used as a dye and as a medication. As a medication, it is mainly used to treat methemoglobinemia. It has previously been used for treating cyanide poisoning and urinary trac ...

-stained spots in red blood cells containing older ''P. falciparum'' parasites. He proposed that these spots were due to injury of the host cell and consumption of host cell materials by the parasite. A more detailed description of Maurer's clefts using electron microscopy was published by William Trager, Maria Rudzinska, and Phyllis Bradbury in 1966.

References

{{Reflist Organelles Plasmodium