The Kelch motif is a region of
protein sequence
Protein primary structure is the linear sequence of amino acids in a peptide or protein. By convention, the primary structure of a protein is reported starting from the amino-terminal (N) end to the carboxyl-terminal (C) end. Protein biosynthesi ...
found widely in proteins from
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
and
eukaryotes
Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
.
This sequence motif is composed of about 50
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...
residues which form a structure of a four stranded beta-sheet "blade". This
sequence motif
In biology, a sequence motif is a nucleotide or amino-acid sequence pattern that is widespread and usually assumed to be related to biological function of the macromolecule. For example, an ''N''-glycosylation site motif can be defined as ''As ...
is found in between five and eight
tandem copies per protein which
fold together to form a larger circular
solenoid
upright=1.20, An illustration of a solenoid
upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines
A solenoid () is a type of electromagnet formed by a helix, helical coil of wire whose ...
structure called a
beta-propeller
In structural biology, a beta-propeller (β-propeller) is a type of all-β protein architecture characterized by 4 to 8 highly symmetrical blade-shaped beta sheets arranged toroidally around a central axis. Together the beta-sheets form a funnel- ...
domain
Domain may refer to:
Mathematics
*Domain of a function, the set of input values for which the (total) function is defined
**Domain of definition of a partial function
**Natural domain of a partial function
**Domain of holomorphy of a function
* Do ...
.
Proteins containing Kelch motifs
The Kelch motif is widely found in eukaryotic and bacterial species. Notably the human genome contains around 100 proteins containing the Kelch motif. Within individual proteins the motif occurs multiple times. For example, the motif appears 6 times in ''
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 species ...
'' egg-chamber regulatory protein. The motif is also found in mouse protein
MIPP and in a number of
poxviruses
''Poxviridae'' is a family of double-stranded DNA viruses. Vertebrates and arthropods serve as natural hosts. There are currently 83 species in this family, divided among 22 genera, which are divided into two subfamilies. Diseases associated wit ...
. In addition, kelch
repeats
A rerun or repeat is a rebroadcast of an episode of a radio or television program. There are two types of reruns – those that occur during a hiatus, and those that occur when a program is syndicated.
Variations
In the United Kingdom, the word ...
have been recognised in alpha- and beta-scruin,
in galactose oxidase from the fungus ''
Dactylium dendroides''
and in the ''
Escherichia coli
''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...
'' NanM protein, that is a
sialic acid mutarotase
N-acetylneuraminate epimerase (, ''sialic acid epimerase'', ''N-acetylneuraminate mutarotase'', sialic acid mutarotase, ''YjhT'', NanM) is an enzyme with systematic name ''N-acetyl-alpha-neuraminate 2-epimerase''. This enzyme catalyses the followi ...
.
Structure
The structure of galactose oxidase reveals that the repeated Kelch sequence motif corresponds to a 4-stranded anti-parallel beta-sheet motif that forms the repeat unit in a super-barrel structural fold commonly known as a beta propeller.
Function
The known functions of kelch-containing proteins are diverse:
*
scruin is an actin cross-linking protein;
*
galactose oxidase catalyses the oxidation of the hydroxyl group at the C6 position in D-galactose;
*
neuraminidase
Exo-α-sialidase (EC 3.2.1.18, sialidase, neuraminidase; systematic name acetylneuraminyl hydrolase) is a glycoside hydrolase that cleaves the glycosidic linkages of neuraminic acids:
: Hydrolysis of α-(2→3)-, α-(2→6)-, α-(2→8)- glycos ...
hydrolyses sialic acid residues from glycoproteins;
* NanM is a sialic acid mutarotase, involved in efficient utilisation of sialic acid by bacteria;
* kelch may have a cytoskeletal function, as it is localised to the actin-rich ring canals that connect the 15 nurse cells to the developing
oocyte
An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The female ...
in Drosophila.
See also
*
WD40 repeat
The WD40 repeat (also known as the WD or beta-transducin repeat) is a short structural motif of approximately 40 amino acids, often terminating in a tryptophan-aspartic acid (W-D) dipeptide. Tandem copies of these repeats typically fold togethe ...
*
Kelch protein
Kelch proteins (and Kelch-like proteins) are a widespread group of proteins that contain multiple Kelch motifs. The kelch domain generally occurs as a set of five to seven kelch tandem repeats that form a β-propeller tertiary structure. Kelch-r ...
References
External links
*
{{Protein tandem repeats