Tektins are

cytoskeletal The cytoskeleton is a complex, dynamic network of interlinking protein filaments present in the cytoplasm of all cells, including those of bacteria and archaea. In eukaryotes, it extends from the cell nucleus to the cell membrane and is compo ...

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, respo ...

s found in

cilia The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike projecti ...

and

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

as structural components of outer doublet

microtubule Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nm and have an inner diameter between 11 an ...

s. They are also present in

centriole In cell biology a centriole is a cylindrical organelle composed mainly of a protein called tubulin. Centrioles are found in most eukaryotic cells, but are not present in conifers (Pinophyta), flowering plants (angiosperms) and most fungi, and a ...

s and

basal bodies A basal body (synonymous with basal granule, kinetosome, and in older cytological literature with blepharoplast) is a protein structure found at the base of a eukaryotic undulipodium (cilium or flagellum). The basal body was named by Theodor W ...

. They are polymeric in nature, and form filaments.MA Pirner and RW Linck
Tektins are heterodimeric polymers in flagellar microtubules with axial periodicities matching the tubulin lattice
J. Biol. Chem., Vol. 269, Issue 50, 31800-31806, Dec, 1994 They include

TEKT1 Tektin-1 is a protein that in humans is encoded by the ''TEKT1'' gene. Function This gene product belongs to the tektin family of proteins. Tektins comprise a family of filament-forming proteins that are coassembled with tubulin Tubulin in m ...

, TEKT2, TEKT3, TEKT4, TEKT5.

Structure

Tektin filaments are 2 to 3 nm diameter with two

alpha helical The alpha helix (α-helix) is a common motif in the secondary structure of proteins and is a right hand-helix conformation in which every backbone N−H group hydrogen bonds to the backbone C=O group of the amino acid located four residues ear ...

segments. They have the consensus amino acid sequence of RPNVELCRD. Different types of tektins, designated as A (53 kDa), B (51 kDa), C (47 kDa) form dimers, trimers and oligomers in various combinations and are also associated with tubulin in the microtubule. Tektins A and B form heteropolymeric protofilaments whereas tektin C forms homodimers. Tektin filaments are present in a

supercoil DNA supercoiling refers to the amount of twist in a particular DNA strand, which determines the amount of strain on it. A given strand may be "positively supercoiled" or "negatively supercoiled" (more or less tightly wound). The amount of a st ...

ed state. This structure of tektins suggests that they are evolutionarily related to

intermediate filament Intermediate filaments (IFs) are cytoskeletal structural components found in the cells of vertebrates, and many invertebrates. Homologues of the IF protein have been noted in an invertebrate, the cephalochordate ''Branchiostoma''. Intermedia ...

s. The proteins are predicted to form extended rods composed of 2 alpha- helical segments (~180 residues long) capable of forming coiled coils, interrupted by non-helical linkers. The 2 segments are similar in sequence, indicating a gene duplication event. Along each tektin rod, cysteine residues occur with a periodicity of ~8 nm, coincident with the axial repeat of tubulin dimers in microtubules. It is proposed that the assembly of tektin heteropolymers produces filaments with repeats of 8, 16, 24, 32, 40, 48 and 96 nm, generating the basis for the complex spatial arrangements of axonemal components.

Function

Tektins as integral components of microtubules are essential for their structural integrity. A mutation in the ''tektin-t''

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

s may lead to defects in flagellar activity which could manifest, for instance, as immotility of

sperm Sperm is the male reproductive cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm with a tail known as a flagellum, whi ...

leading to

male infertility Male infertility refers to a sexually mature male's inability to impregnate a fertile female. In humans it accounts for 40–50% of infertility. It affects approximately 7% of all men. Male infertility is commonly due to deficiencies in the semen, ...

. Tektins are thought to be involved in the assembly of the

basal body A basal body (synonymous with basal granule, kinetosome, and in older cytological literature with blepharoplast) is a protein structure found at the base of a eukaryotic undulipodium (cilium or flagellum). The basal body was named by Theodor W ...

. The study of tektins has also been found to be useful in

phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...

, to establish evolutionary relationship between organisms.

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 ...

sequences of tektins are well conserved, with significant similarity between mouse and human

homologs A couple of homologous chromosomes, or homologs, are a set of one maternal and one paternal chromosome that pair up with each other inside a cell during fertilization. Homologs have the same genes in the same loci where they provide points alon ...

References

{{Cytoskeletal Proteins Protein families

Structure

Function

See also

References