Unconventional myosin-VI, is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...

that in humans is coded for by ''MYO6''. Unconventional myosin-VI is a

myosin Myosins () are a superfamily of motor proteins best known for their roles in muscle contraction and in a wide range of other motility processes in eukaryotes. They are ATP-dependent and responsible for actin-based motility. The first myosin (M ...

molecular motor involved in intracellular

vesicle Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry) In cell biology, a vesicle is a structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer. Vesicles form nat ...

and

organelle In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' th ...

transport.

Structure

Human myosin-VI contains a N-terminal myosin head domain (residues 59–759), two

coiled coil A coiled coil is a structural motif in proteins in which 2–7 alpha-helices are coiled together like the strands of a rope. (Dimers and trimers are the most common types.) Many coiled coil-type proteins are involved in important biological fu ...

motifs (residues 902–984 and 986–1009 respectively), and a C-terminal myosin VI cargo binding domain (residues 1177–1267).

Function

Unconventional myosin-VI is unique because it travels in the opposite direction of other myosins, towards the negative end of

actin filament Microfilaments, also called actin filaments, are protein filaments in the cytoplasm of eukaryotic cells that form part of the cytoskeleton. They are primarily composed of polymers of actin, but are modified by and interact with numerous other pro ...

s. Myosin-VI follows the same structure as other myosin but with two unique "inserts" allowing for its diversified properties. One insert is called the "reverse gear" and is responsible for its movement towards the negative end of actin filaments. The reverse gear is located on the neck region of the myosin and acts as a reorienting device for the lever arm to move backwards after myosin movement. The second insert assists in regulating ATP enzyme activity located in the motor head domain. There are 3 amino acid binding sites essential for myosin-VI's interactions, Arg-Arg-Leu and Trp-Trp-Tyr in the tail region and Met-Ile-Sec in the helix. The Arg-Arg-Leu amino acid segment (abbreviated RRL) takes part in ubiquitin interactions while Trp-Trp-Tyr (abbreviated WWY) assists in interactions with DAB2. Myosin-VI's Met-Ile-Sec bonding interactions are limited to the myosin-VI long isoform but interact with clathrin in endocytosis. Myosin-VI long isoform is formed by the inclusion of exon 31, adding an addition alpha-helix, restriction RRL interactions. Myosin-VI long struggles to interact with ubiquitin chains and GIPC1 due to this structural formation, however, increases attractivity to clathrin. Myosin-VI's structural flexibility provides a great width in interaction ability with its environment and interactors.

Interactions

MYO6 has been shown to

interact Advocates for Informed Choice, doing business as, dba interACT or interACT Advocates for Intersex Youth, is a 501(c)(3) nonprofit organization using innovative strategies to advocate for the legal and human rights of children with intersex trai ...

with

GIPC1 GIPC PDZ domain containing family, member 1 (GIPC1) is a protein that in humans is encoded by the ''GIPC1'' gene. GIPC was originally identified as it binds specifically to the C terminus of RGS-GAIP, a protein involved in the regulation of G prot ...

, DAB2.,

ubiquitin Ubiquitin is a small (8.6 kDa) regulatory protein found in most tissues of eukaryotic organisms, i.e., it is found ''ubiquitously''. It was discovered in 1975 by Gideon Goldstein and further characterized throughout the late 1970s and 1980s. Fo ...

, and

clathrin Clathrin is a protein that plays a major role in the formation of coated vesicles. Clathrin was first isolated and named by Barbara Pearse in 1976. It forms a triskelion shape composed of three clathrin heavy chains and three light chains. When ...

. Myosin VI, being a motor protein, focuses its interactions by moving along actin filaments. This however does not limit its functions, because MYO6 is heavily involved in cytokinesis, creation of membrane compartments, and the regulation and organization of actin filaments.

Clinical significance

Mutations in the MYO6 gene are associated with hearing loss. MYO6 has also been found to be involved in many events in

spermiogenesis Spermiogenesis is the final stage of spermatogenesis, during which the spermatids develop into mature spermatozoa. At the beginning of the stage, the spermatid is a more or less circular cell containing a nucleus, Golgi apparatus, centriole an ...

in numerous different creatures. In common fruit flies (

Drosophila ''Drosophila'' () is a genus of flies, belonging to the family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many speci ...

), the myosin-VI ortholog controls the sterility of males by organization of actin involved in spermatid individualization. This same ortholog in roundworms (

C. elegans ''Caenorhabditis elegans'' () is a free-living transparent nematode about 1 mm in length that lives in temperate soil environments. It is the type species of its genus. The name is a blend of the Greek ''caeno-'' (recent), ''rhabditis'' (r ...

) regulates the separation of cytosol in spermatid formation due to its influence in cytokinesis. In mice, this ortholog will control specialization and membrane compartment creation.

References

External links