A HEAT repeat is a protein tandem repeat

structural motif In a polymer, chain-like biological molecule, such as a protein or nucleic acid, a structural motif is a common Biomolecular structure#Tertiary structure, three-dimensional structure that appears in a variety of different, evolutionarily unrel ...

composed of two

alpha helices 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 ...

linked by a short loop. HEAT repeats can form

alpha solenoid An alpha solenoid (sometimes also known as an alpha horseshoe or as stacked pairs of alpha helices, abbreviated SPAH) is a protein fold composed of repeating alpha helix subunits, commonly helix-turn-helix motifs, arranged in antiparallel fashi ...

s, a type of

solenoid protein domain Solenoid protein domains are a highly modular type of protein domain. They consist of a chain of nearly identical folds, often simply called tandem repeats. They are extremely common among all types of proteins, though exact figures are unknown. ...

found in a number of

cytoplasm In cell biology, the cytoplasm is all of the material within a eukaryotic cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm. The ...

ic proteins. The name "HEAT" is an acronym for four proteins in which this repeat structure is found: Huntingtin, elongation factor 3 (EF3),

protein phosphatase 2 Protein phosphatase 2 (PP2), also known as PP2A, is an enzyme that in humans is encoded by the ''PPP2CA'' gene. The PP2A heterotrimeric protein phosphatase is ubiquitously expressed, accounting for a large fraction of phosphatase activity in eu ...

A (PP2A), and the yeast kinase TOR1. HEAT repeats form extended superhelical structures which are often involved in intracellular transport; they are structurally related to

armadillo repeats An armadillo repeat is the name of a characteristic, repetitive amino acid sequence of about 40 residues in length that is found in many proteins. Proteins that contain armadillo repeats typically contain several tandemly repeated copies. Each a ...

. The nuclear transport protein

importin beta Importin is a type of karyopherin that transports protein molecules from the cell's cytoplasm to the nucleus. It does so by binding to specific recognition sequences, called nuclear localization sequences (NLS). Importin has two subunits, import ...

contains 19 HEAT repeats.

Various HEAT repeat proteins and their structures

Representative examples of HEAT repeat proteins include

importin Importin is a type of karyopherin that transports protein molecules from the cell's cytoplasm to the nucleus. It does so by binding to specific recognition sequences, called nuclear localization sequences (NLS). Importin has two subunits, impo ...

β (also known as karyopherin β) family, regulatory subunits of

condensin Condensins are large protein complexes that play a central role in chromosome assembly and segregation during mitosis and meiosis (Figure 1). Their subunits were originally identified as major components of mitotic chromosomes assembled in ''Xeno ...

and

cohesin Cohesin is a protein complex that mediates sister chromatid cohesion, homologous recombination, and DNA looping. Cohesin is formed of SMC3, SMC1, SCC1 and SCC3 ( SA1 or SA2 in humans). Cohesin holds sister chromatids together after DNA rep ...

, separase, PIKKs (phosphatidylinositol 3-kinase-related protein kinases) such as ATM ( Ataxia telangiectasia mutated) and ATR (

Ataxia telangiectasia and Rad3 related Serine/threonine-protein kinase ATR also known as ataxia telangiectasia and Rad3-related protein (ATR) or FRAP-related protein 1 (FRP1) is an enzyme that, in humans, is encoded by the ''ATR'' gene. It is a large kinase of about 301.66 kDa. ATR bel ...

), and the microtubule-binding protein XMAP215/Dis1/TOG and CLASP. Thus, cellular functions of HEAT repeat proteins are highly variable. The structure of the following HEAT repeat proteins have been determined so far: *Protein modification and degradation **A subunit and holoenzyme of PP2A **SCF

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 ...

ligase regulator Cand1 **Hsm3, a molecular chaperon involved in the assembly of 26S

proteasome Proteasomes are protein complexes which degrade unneeded or damaged proteins by proteolysis, a chemical reaction that breaks peptide bonds. Enzymes that help such reactions are called proteases. Proteasomes are part of a major mechanism by w ...

*Nucleo-cytoplasmic transport **

Importin Importin is a type of karyopherin that transports protein molecules from the cell's cytoplasm to the nucleus. It does so by binding to specific recognition sequences, called nuclear localization sequences (NLS). Importin has two subunits, impo ...

β **Exportin Cse1 **Transportin 1 **Nuleoporin Gle1; Nup188; Nup192 *

Transcriptional regulation In molecular biology and genetics, transcriptional regulation is the means by which a cell regulates the conversion of DNA to RNA (transcription), thereby orchestrating gene activity. A single gene can be regulated in a range of ways, from alt ...

**TFIID subunit TAF6 **TBP regulator Mot1（Modifier of transcription 1） **Transcriptional initiation factor Rrn3 *

Translational regulation Translational regulation refers to the Regulation of gene expression, control of the levels of protein synthesized from its mRNA. This regulation is vastly important to the cellular response to stressors, growth cues, and Cellular differentiation, d ...

**Elongation factor eEF3 **Initiation factor eIF4G **

Aminoacyl tRNA synthetase An aminoacyl-tRNA synthetase (aaRS or ARS), also called tRNA-ligase, is an enzyme that attaches the appropriate amino acid onto its corresponding tRNA. It does so by catalyzing the transesterification of a specific cognate amino acid or its pre ...

transfer protein Cex1p *DNA repair **DNA-PK ( DNA-dependent protein kinase) **

Fanconi anemia Fanconi anaemia (FA) is a rare genetic disease resulting in impaired response to DNA damage. Although it is a very rare disorder, study of this and other bone marrow failure syndromes has improved scientific understanding of the mechanisms of nor ...

responsible protein FANCF (

FANCF Fanconi anemia group F protein is a protein that in humans is encoded by the ''FANCF'' gene. Interactions FANCF has been shown to interact with Fanconi anemia, complementation group C, FANCG, FANCA and FANCE. Function FANCF is an adaptor pro ...

) **Damaged DNA-binding protein AlkD (Alkylpurin DNA glycosylase) **PIKKs chaperone Tel2 *Chromosomal regulation **

Cohesin Cohesin is a protein complex that mediates sister chromatid cohesion, homologous recombination, and DNA looping. Cohesin is formed of SMC3, SMC1, SCC1 and SCC3 ( SA1 or SA2 in humans). Cohesin holds sister chromatids together after DNA rep ...

subunit SA2/Scc3 **

regulator Wapl **

regulator Pds5 **

loading factor Scc2 **

protease Separase **

Condensin Condensins are large protein complexes that play a central role in chromosome assembly and segregation during mitosis and meiosis (Figure 1). Their subunits were originally identified as major components of mitotic chromosomes assembled in ''Xeno ...

subunit CAP-G/ycg1 **

subunit CAP-D2/ycs4 *Cytoskeletal regulation **

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 ...

-binding protein TOG/Stu2 *Cell proliferation regulation **TOR (

target of rapamycin The mammalian target of rapamycin (mTOR), also referred to as the mechanistic target of rapamycin, and sometimes called FK506-binding protein 12-rapamycin-associated protein 1 (FRAP1), is a kinase that in humans is encoded by the ''MTOR'' gene. ...

) *Others **API5 (Apoptosis inhibitor 5) **V-type ATPase H subunit

References

External links

* * {{Protein tandem repeats