The testis-enhanced gene transcript (TEGT) family includes the testis-enhanced gene transcript proteins of mammals, which are expressed at high levels in the testis, the putative glutamate/aspartate binding proteins of plants and animals, the YccA protein of ''

Escherichia coli ''Escherichia coli'' ( )Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. is a gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus '' Escherichia'' that is commonly fo ...

'' and the YetJ protein of ''

Bacillus subtilis ''Bacillus subtilis'' (), known also as the hay bacillus or grass bacillus, is a gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants, humans and marine sponges. As a member of the genus ''Bacill ...

''. These proteins are about 200-250 residues in length and exhibit 7 TMSs.

Homology

Homologues are found in a variety of

Gram-negative Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists ...

and

Gram-positive bacteria In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall. The Gram stain ...

, yeast, fungi, plants, animals and viruses. The ''E. coli'' genome encodes three paralogues, YbhL, YbhM and YccA. Distant homologues found in '' Drosophilia melanogaster'' and the rat are the N-methyl-D-aspartate receptor-associated protein (NMDARAI) and the N-methyl-D-aspartate receptor glutamate binding chain, respectively. Two others are the rat neural membrane protein 35 and the ''

Arabidopsis thaliana ''Arabidopsis thaliana'', the thale cress, mouse-ear cress or arabidopsis, is a small plant from the mustard family (Brassicaceae), native to Eurasia and Africa. Commonly found along the shoulders of roads and in disturbed land, it is generally ...

'' Bax inhibitor-1 (BI-1) protein capable of suppressing Bax-induced cell death in

yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom (biology), kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are est ...

BI-1

One of these proteins, TEGT or the Bax Inhibitor-1
TC# 1.A.14.1.1
, has a C-terminal domain that forms a Ca²⁺-permeable channel. BI-1 is an ER-localized protein that protects against

apoptosis Apoptosis (from ) is a form of programmed cell death that occurs in multicellular organisms and in some eukaryotic, single-celled microorganisms such as yeast. Biochemistry, Biochemical events lead to characteristic cell changes (Morphology (biol ...

and ER stress. BI-1 has been proposed to modulate ER Ca²⁺

homeostasis In biology, homeostasis (British English, British also homoeostasis; ) is the state of steady internal physics, physical and chemistry, chemical conditions maintained by organism, living systems. This is the condition of optimal functioning fo ...

by acting as a Ca²⁺-leak channel. These proteins are distantly related to the ionotropic glutamate-binding protein of the N-methyl D-aspartate (NMDA) receptor of man. Homologues include a putative cold shock inducible protein and a SecY stabilizing protein.

Function

Based on experimental determination of the BI-1 topology, Bultynck et al. proposes that its C-terminal α-helical 20 amino acid peptide catalyzes Ca²⁺ flux both ''in vivo'' and ''in vitro''. The Ca²⁺-leak properties were conserved among animal, but not plant and yeast orthologs. By mutating one of the critical aspartate residues (D₂₁₃) in the proposed Ca²⁺-channel pore in full-length BI-1, D₂₁₃ proved to be essential for BI-1 dependent ER Ca²⁺-leak.

Structure

Chang ''et al.'' published

crystal structures In crystallography, crystal structure is a description of ordered arrangement of atoms, ions, or molecules in a crystalline material. Ordered structures occur from intrinsic nature of constituent particles to form symmetric patterns that repeat a ...

of a bacterial homolog, YetJ
TC# 1.A.14.2.3
at 1.9 Å resolution and characterized its calcium leak activity. Its seven-transmembrane-helix fold features two triple-helix sandwiches wrapped around a central C-terminal helix. Structures obtained in closed and open conformations are reversibly interconvertible by changes in the pH. A hydrogen-bonded perturbed pair of conserved aspartyl residues explains the pH dependence of this transition, and the pH regulates calcium influx in proteoliposomes. Homology models for human BI-1 provided insight into its cytoprotective activity.

Transport Reaction

The generalized reaction catalyzed by TEGT channels is: : cations (out) ⇌ cations (in)

References

{{CCBYSASource, sourcepath=http://tcdb.org/search/result.php?tc=1.A.14, sourcearticle=1.A.14 The Testis-Enhanced Gene Transfer (TEGT) Family, revision=699838558 Protein families Membrane proteins Transmembrane proteins Transmembrane transporters Transport proteins Integral membrane proteins