Dedicator of cytokinesis protein 9 (Dock9), also known as Zizimin1, is a large (~230 kDa)

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, respon ...

encoded in the human by the ''DOCK9'' gene, involved in

intracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...

signalling networks. It is a member of the DOCK-D subfamily of the

DOCK A dock (from Dutch ''dok'') is the area of water between or next to one or a group of human-made structures that are involved in the handling of boats or ships (usually on or near a shore) or such structures themselves. The exact meaning va ...

family of

guanine nucleotide exchange factor Guanine nucleotide exchange factors (GEFs) are proteins or protein domains that activate monomeric GTPases by stimulating the release of guanosine diphosphate (GDP) to allow binding of guanosine triphosphate (GTP). A variety of unrelated struct ...

s that function as activators of

small G-protein Small GTPases (), also known as small G-proteins, are a family of hydrolase enzymes that can bind and hydrolyze guanosine triphosphate (GTP). They are a type of G-protein found in the cytosol that are homologous to the alpha subunit of heterotrim ...

s. Dock9 activates the small G protein Cdc42.

Discovery

Dock9 was discovered using an affinity

proteomic Proteomics is the large-scale study of proteins. Proteins are vital parts of living organisms, with many functions such as the formation of structural fibers of muscle tissue, enzymatic digestion of food, or synthesis and replication of DNA. In ...

approach designed to identify novel activators of the small G protein Cdc42 in

fibroblast A fibroblast is a type of biological cell that synthesizes the extracellular matrix and collagen, produces the structural framework ( stroma) for animal tissues, and plays a critical role in wound healing. Fibroblasts are the most common cells of ...

s. Subsequent

northern blot The northern blot, or RNA blot,Gilbert, S. F. (2000) Developmental Biology, 6th Ed. Sunderland MA, Sinauer Associates. is a technique used in molecular biology research to study gene expression by detection of RNA (or isolated mRNA) in a sample.Ke ...

analysis revealed that Dock9 is expressed primarily in the

brain The brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head ( cephalization), usually near organs for special ...

heart The heart is a muscular organ found in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon diox ...

skeletal muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of m ...

kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; bloo ...

placenta The placenta is a temporary embryonic and later fetal organ (anatomy), organ that begins embryonic development, developing from the blastocyst shortly after implantation (embryology), implantation. It plays critical roles in facilitating nutrien ...

and lung. Lower levels were detected in the colon,

thymus The thymus is a specialized primary lymphoid organ of the immune system. Within the thymus, thymus cell lymphocytes or ''T cells'' mature. T cells are critical to the adaptive immune system, where the body adapts to specific foreign invaders. ...

liver The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...

small intestine The small intestine or small bowel is an organ in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through t ...

and in

leukocyte White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from mul ...

s from peripheral blood.

Structure and function

Dock9 shares a similar structure of two core domains (known as DHR1 and DHR2), which are shared by all DOCK family members. The

C-terminal The C-terminus (also known as the carboxyl-terminus, carboxy-terminus, C-terminal tail, C-terminal end, or COOH-terminus) is the end of an amino acid chain (protein or polypeptide), terminated by a free carboxyl group (-COOH). When the protein is ...

DHR2 domain functions as an atypical GEF domain for small G proteins (see Dock180: structure and function) and the DHR1 domain is known, in some DOCK-A/B/C subfamily proteins, to be involved in their recruitment to the

plasma membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (t ...

. Unlike DOCK-A/B/C proteins DOCK-D proteins (including Dock9) contain an N-terminal pleckstrin homology (PH) domain that mediates their recruitment to the membrane. Dock9, along with other DOCK-C/D subfamily members, can activate Cdc42 ''

in vitro ''In vitro'' (meaning in glass, or ''in the glass'') studies are performed with microorganisms, cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in biology and ...

'' and ''

in vivo Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, and ...

'' via its DHR2 domain. However, Dock9 adopts an autoinhibitory conformation that masks the DHR2 domain in its resting state. The mechanism by which this autoinhibition is overcome is still unclear although in some other DOCK proteins, which also undergo autoinhibition, it requires an interaction with adaptor proteins such as

ELMO Elmo is a red Muppet monster character on the long-running PBS/ HBO children's television show ''Sesame Street''. A furry red monster who has a falsetto voice and illeism, he hosts the last full five-minute segment (fifteen minutes prior ...

. Dock9 has also been reported to

dimer Dimer may refer to: * Dimer (chemistry), a chemical structure formed from two similar sub-units ** Protein dimer, a protein quaternary structure ** d-dimer * Dimer model, an item in statistical mechanics, based on ''domino tiling'' * Julius Dimer ( ...

ise, under resting conditions, via its DHR2 domains and this study suggests that other DOCK family proteins may also behave in the same way. Recent analysis of a

chromosomal A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

region associated with susceptibility to

bipolar disorder Bipolar disorder, previously known as manic depression, is a mental disorder characterized by periods of depression and periods of abnormally elevated mood that last from days to weeks each. If the elevated mood is severe or associated with ...

revealed that single nucleotide polymorphisms in the ''DOCK9'' gene contribute to the risk and severity of this condition.

Discovery

Structure and function

References

Further reading