Alexandre G. Petrenko, Ph.D.

Dissociation of the subunits of the calcium-independent receptor of alpha-latrotoxin as a result of two-step proteolysis
Krasnoperov, Valery; Deyev, Igor E; Serova, Oxana V; Xu, Chongfeng; Lu, Yun; Buryanovsky, Leonid; Gabibov, Alexander G; Neubert, Thomas A; Petrenko, Alexander G
2009 Apr 14;48(14):3230-3238, Biochemistry
CIRL (the calcium-independent receptor of alpha-latrotoxin), a neuronal cell surface receptor implicated in the regulation of exocytosis, is a member of the GPS family of chimeric cell adhesion/G protein-coupled receptors. The predominant form of CIRL is a membrane-bound complex of two subunits, p120 and p85. Extracellularly oriented p120 contains hydrophilic cell adhesion domains, whereas p85 is a heptahelical membrane protein. Both subunits are encoded by the same gene and represent products of intracellular proteolytic processing of the CIRL precursor. In this study, we demonstrate that a soluble form of CIRL also exists in vitro and in vivo. It results from the further cleavage of CIRL by a second protease. The site of the second cleavage is located in the short N-terminal extracellular tail of p85, between the GPS domain and the first transmembrane segment of CIRL. Thus, the soluble form of CIRL represents a complex of p120 noncovalently bound to a 15 amino acid residue N-terminal peptide fragment of p85. We have previously shown that mutations of CIRL in the GPS domain inhibit intracellular proteolytic processing and also result in the absence of the receptors from the cell surface. Our current data suggest that although CIRL trafficking to the cell membrane is impaired by mutations in the GPS region, it is not blocked completely. However, at the cell surface, the noncleaved mutants are preferentially targeted by the second protease that sheds the extracellular subunit. Therefore, the two-step proteolytic processing may represent a regulatory mechanism that controls cell surface expression of membrane-bound and soluble forms of CIRL
— id: 98778, year: 2009, vol: 48, page: 3230, stat: Journal Article,

Evidence of the receptor for cocaine and amphetamine regulated transcript ( CART ) in GH3 cells and bovine anterior pituitary
Berman, Y.; Lukyanov, Y. S.; Tkalych, O.; Fiallo, A.; Helmer, E.; Petrenko, A.; Carr, K. D.
2003 ;2003:?-?, Society for Neuroscience Abstract Viewer & Itinerary Planner
Cocaine-and Amphetamine Regulated Transcript (CART) was first identified as a mRNA upregulated in striatum in response to acute injection of cocaine and amphetamine. The CART transcript encodes for a protein (Pro-CART) which is processed to smaller forms of bioactive peptides, CART 55-102 and CART 62-102. The subcellular localization of CART peptides within dense core vesicles of axon terminals suggests a neurotransmitter role for these peptides. However, CART receptors have not been identified. In the present study, saturable specific binding of (125I) CART was demonstrated in GH3 cells (a rat pituitary adenoma cell line) and bovine anterior pituitary. Further, it was shown by confocal microscopy in live cells that activation of these binding sites results in translocation of beta-arrestin2/green fluorescent protein (beta-arr2-GFP) to the plasma membrane, suggesting that CART binding sites are G-protein coupled receptors. Analysis of receptor-mediated signal transduction revealed that CART peptides inhibit forskolin-stimulated cAMP production in a pertussis toxin-sensitive manner, suggesting that the CART binding site is coupled to Gi/o proteins. CART peptides also activated Mitogen Activated Protein Kinase (MAPK) in a time and dose dependent manner, with significantly different time courses for the 55-102 and 62-102 fragments. Together, these results indicate that cellular effects of CART peptides are mediated by membrane G-protein coupled receptors with negative and positive coupling to cAMP and MAPK signaling pathways, respectively
— id: 92205, year: 2003, vol: 2003, page: ?, stat: Journal Article,

Protein-tyrosine Phosphatase-sigma Is a Novel Member of the Functional Family of alpha -Latrotoxin Receptors
Krasnoperov, Valery; Bittner, Mary A; Mo, Wenjun; Buryanovsky, Leonid; Neubert, Thomas A; Holz, Ronald W; Ichtchenko, Konstantin; Petrenko, Alexander G
2002 Sep 27;277(39):35887-35895, Journal of biological chemistry
Receptor-like protein-tyrosine phosphatase sigma (PTPvarsigma) is essential for neuronal development and function. Here we report that PTPvarsigma is a target of alpha-latrotoxin, a strong stimulator of neuronal exocytosis. alpha-Latrotoxin binds to the cell adhesion-like extracellular region of PTPvarsigma. This binding results in the stimulation of exocytosis. The toxin-binding site is located in the C-terminal part of the PTPvarsigma ectodomain and includes two fibronectin type III repeats. The intracellular catalytic domains of PTPvarsigma are not required for the alpha-latrotoxin binding and secretory response triggered by the toxin in chromaffin cells. These features of PTPvarsigma resemble two other previously described alpha-latrotoxin receptors, neurexin and CIRL. Thus, alpha-latrotoxin represents an unusual example of the neurotoxin that has three independent, equally potent, and yet structurally distinct targets. The known structural and functional characteristics of PTPvarsigma, neurexin, and CIRL suggest that they define a functional family of neuronal membrane receptors with complementary or converging roles in presynaptic function via a mechanism that involves cell-to-cell and cell-to-matrix interaction
— id: 32497, year: 2002, vol: 277, page: 35887, stat: Journal Article,

Post-translational proteolytic processing of the calcium-independent receptor of alpha-latrotoxin (CIRL), a natural chimera of the cell adhesion protein and the G protein-coupled receptor. Role of the G protein-coupled receptor proteolysis site (GPS) motif
Krasnoperov, Valery; Lu, Yun; Buryanovsky, Leonid; Neubert, Thomas A; Ichtchenko, Konstantin; Petrenko, Alexander G
2002 Nov 29;277(48):46518-46526, Journal of biological chemistry
The calcium-independent receptor of alpha-latrotoxin (CIRL), a neuronal cell surface receptor implicated in the regulation of exocytosis, is a natural chimera of the cell adhesion protein and the G protein-coupled receptor (GPCR). In contrast with canonic GPCRs, CIRL consists of two heterologous non-covalently bound subunits, p120 and p85, due to endogenous proteolytic processing of the receptor precursor in the endoplasmic reticulum. Extracellularly oriented p120 contains hydrophilic cell adhesion domains, whereas p85 resembles a generic GPCR. We determined that the site of the CIRL cleavage is located within a juxtamembrane Cys- and Trp-rich domain of the N-terminal extracellular region of CIRL. Mutations in this domain make CIRL resistant to the cleavage and impair its trafficking. Therefore, we have named it GPS for G protein-coupled receptor proteolysis site. The GPS motif is found in homologous adhesion GPCRs and thus defines a novel receptor family. We postulate that the proteolytic processing and two-subunit structure is a common characteristic feature in the family of GPS-containing adhesion GPCRs
— id: 33173, year: 2002, vol: 277, page: 46518, stat: Journal Article,

The functional family of alpha-latrotoxin receptors
Krasnoperov, V; Ichtchenko, K; Petrenko, AG
2001 JUN ;77(1-2):6-7, Journal of neurochemistry
— id: 55017, year: 2001, vol: 77, page: 6, stat: Journal Article,

Calcium-independent receptor for alpha-latrotoxin and neurexin 1alpha [corrected] facilitate toxin-induced channel formation: evidence that channel formation results from tethering of toxin to membrane
Hlubek MD; Stuenkel EL; Krasnoperov VG; Petrenko AG; Holz RW
2000 Mar;57(3):519-528, Molecular pharmacology
alpha-Latrotoxin binding to the calcium-independent receptor for alpha-latrotoxin (CIRL-1), a putative G-protein-coupled receptor, stimulates secretion from chromaffin and PC12 cells. Using patch clamp techniques and microspectrofluorimetry, we demonstrate that the interaction of alpha-latrotoxin with CIRL-1 produces a high conductance channel that permits increases in cytosolic Ca(2+). alpha-Latrotoxin interaction with CIRL-1 transiently expressed in bovine chromaffin cells produced a 400-pS channel, which rarely closed under Ca(2+)-free conditions. The major effect of overexpressing CIRL-1 was to greatly increase the sensitivity of chromaffin cells to channel formation by alpha-latrotoxin. alpha-Latrotoxin interaction with CIRL-1 transiently overexpressed in non-neuronal human embryonic kidney 293 (HEK293) cells produced channels that were nearly identical with those observed in chromaffin cells. Channel currents were reduced by millimolar Ca(2+). At alpha-latrotoxin concentrations below 500 pM, channel formation occurred many seconds after binding of toxin to CIRL-1 indicating distinct steps in channel formation. In all cases there was a rapid, sequential addition of channels once the first channel appeared. An analysis of CIRL-1 mutants indicated that channel formation in HEK293 cells is unlikely to be transduced by a G-protein-dependent mechanism. alpha-Latrotoxin interaction with a fusion construct composed of the extracellular domain of CIRL-1 anchored to the membrane by the transmembrane domain of vesicular stomatitis virus glycoprotein, and with neurexin 1alpha, an alpha-latrotoxin receptor structurally unrelated to CIRL-1, produced channels virtually identical with those observed with wild-type CIRL-1. We propose that alpha-latrotoxin receptors recruit toxin to facilitate its insertion across the membrane and that alpha-latrotoxin itself controls the conductance properties of the channels it produces
— id: 57555, year: 2000, vol: 57, page: 519, stat: Journal Article,

A novel ubiquitously expressed alpha-latrotoxin receptor is a member of the CIRL family of G-protein-coupled receptors
Ichtchenko K; Bittner MA; Krasnoperov V; Little AR; Chepurny O; Holz RW; Petrenko AG
1999 Feb 26;274(9):5491-5498, Journal of biological chemistry
Poisoning with alpha-latrotoxin, a neurotoxic protein from black widow spider venom, results in a robust increase of spontaneous synaptic transmission and subsequent degeneration of affected nerve terminals. The neurotoxic action of alpha-latrotoxin involves extracellular binding to its high affinity receptors as a first step. One of these proteins, CIRL, is a neuronal G-protein-coupled receptor implicated in the regulation of secretion. We now demonstrate that CIRL has two close homologs with a similar domain structure and high degree of overall identity. These novel receptors, which we propose to name CIRL-2 and CIRL-3, together with CIRL (CIRL-1) belong to a recently identified subfamily of large orphan receptors with structural features typical of both G-protein-coupled receptors and cell adhesion proteins. Northern blotting experiments indicate that CIRL-2 is expressed ubiquitously with highest concentrations found in placenta, kidney, spleen, ovary, heart, and lung, whereas CIRL-3 is expressed predominantly in brain similarly to CIRL-1. It appears that CIRL-2 can also bind alpha-latrotoxin, although its affinity to the toxin is about 14 times less than that of CIRL-1. When overexpressed in chromaffin cells, CIRL-2 increases their sensitivity to alpha-latrotoxin stimulation but also inhibits Ca2+-regulated secretion. Thus, CIRL-2 is a functionally competent receptor of alpha-latrotoxin. Our findings suggest that although the nervous system is the primary target of low doses of alpha-latrotoxin, cells of other tissues are also susceptible to the toxic effects of alpha-latrotoxin because of the presence of CIRL-2, a low affinity receptor of the toxin
— id: 7354, year: 1999, vol: 274, page: 5491, stat: Journal Article,

Structural requirements for alpha-latrotoxin binding and alpha-latrotoxin-stimulated secretion. A study with calcium-independent receptor of alpha-latrotoxin (CIRL) deletion mutants
Krasnoperov V; Bittner MA; Holz RW; Chepurny O; Petrenko AG
1999 Feb 5;274(6):3590-3596, Journal of biological chemistry
Stimulation of neurotransmitter release by alpha-latrotoxin requires its binding to the calcium-independent receptor of alpha-latrotoxin (CIRL), an orphan neuronal G protein-coupled receptor. CIRL consists of two noncovalently bound subunits, p85, a heptahelical integral membrane protein, and p120, a large extracellular polypeptide with domains homologous to lectin, olfactomedin, mucin, the secretin receptor family, and a novel structural motif common for large orphan G protein-coupled receptors. The analysis of CIRL deletion mutants indicates that the high affinity alpha-latrotoxin-binding site is located within residues 467-891, which comprise the first transmembrane segment of p85 and the C-terminal half of p120. The N-terminal lectin, olfactomedin, and mucin domains of p120 are not required for the interaction with alpha-latrotoxin. Soluble p120 and all its fragments, which include the 467-770 residues, bind alpha-latrotoxin with low affinity suggesting the importance of membrane-embedded p85 for the stabilization of the complex of the toxin with p120. Two COOH-terminal deletion mutants of CIRL, one with the truncated cytoplasmic domain and the other with only one transmembrane segment left of seven, supported both alpha-latrotoxin-induced calcium uptake in HEK293 cells and alpha-latrotoxin-stimulated secretion when expressed in chromaffin cells, although with a different dose dependence than wild-type CIRL and its N-terminal deletion mutant. Thus the signaling domains of CIRL are not critically important for the stimulation of exocytosis in intact chromaffin cells by alpha-latrotoxin
— id: 7375, year: 1999, vol: 274, page: 3590, stat: Journal Article,

The CIRLs, a novel family of two-subunit G protein-coupled receptors with structural features of cell adhesion proteins
Petrenko, AG; Krasnoperov, V; Ichtchenko, K
1999 APR 23 ;13(7):A1578-A1578, FASEB journal
— id: 53942, year: 1999, vol: 13, page: A1578, stat: Journal Article,

A Ca2+-independent receptor for alpha-latrotoxin, CIRL, mediates effects on secretion via multiple mechanisms
Bittner MA; Krasnoperov VG; Stuenkel EL; Petrenko AG; Holz RW
1998 Apr 15;18(8):2914-2922, Journal of neuroscience
alpha-Latrotoxin (alpha-Ltx), a component of black widow spider venom, stimulates secretion from nerve terminals and from PC12 cells. In this study we examine the effects of expression of a newly cloned Ca2+-independent receptor for alpha-Ltx (CIRL) on secretion from bovine chromaffin cells. We first characterized the effect of alpha-Ltx on secretion from untransfected cells. alpha-Ltx, by binding in a Ca2+-independent manner to an endogenous receptor, causes subsequent Ca2+-dependent secretion from intact cells. The stimulation of secretion is correlated with Ca2+ influx caused by the toxin. In permeabilized cells in which the Ca2+ concentration is regulated by buffer, alpha-Ltx also enhances Ca2+-dependent secretion, indicating a direct role of the endogenous receptor in the secretory pathway. Expression of CIRL increased the sensitivity of intact and permeabilized cells to the effects of alpha-Ltx, demonstrating that this protein is functional in coupling to secretion. Importantly, in the absence of alpha-Ltx, the expression of CIRL specifically inhibited the ATP-dependent component of secretion in permeabilized cells without affecting the ATP-independent secretion. This suggests that this receptor modulates the normal function of the regulated secretory pathway and that alpha-Ltx may act by reversing the inhibitory effects of the receptor
— id: 7504, year: 1998, vol: 18, page: 2914, stat: Journal Article,

alpha-Latrotoxin stimulates exocytosis by the interaction with a neuronal G-protein-coupled receptor
Krasnoperov VG; Bittner MA; Beavis R; Kuang Y; Salnikow KV; Chepurny OG; Little AR; Plotnikov AN; Wu D; Holz RW; Petrenko AG
1997 Jun;18(6):925-937, Neuron
alpha-Latrotoxin is a potent stimulator of neurosecretion. Its action requires extracellular binding to high affinity presynaptic receptors. Neurexin I alpha was previously described as a high affinity alpha-latrotoxin receptor that binds the toxin only in the presence of calcium ions. Therefore, the interaction of alpha-latrotoxin with neurexin I alpha cannot explain how alpha-latrotoxin stimulates neurotransmitter release in the absence of calcium. We describe molecular cloning and functional expression of the calcium-independent receptor of alpha-latrotoxin (CIRL), which is a second high affinity alpha-latrotoxin receptor that may be the major mediator of alpha-latrotoxin's effects. CIRL appears to be a novel orphan G-protein-coupled receptor, a member of the secretin receptor family. In contrast with other known serpentine receptors, CIRL has two subunits of the 120 and 85 kDa that are the result of endogenous proteolytic cleavage of a precursor polypeptide. CIRL is found in brain where it is enriched in the striatum and cortex. Expression of CIRL in chromaffin cells increases the sensitivity of the cells to the effects of alpha-latrotoxin, demonstrating that this protein is functional in coupling to secretion. Syntaxin, a component of the fusion complex, copurifies with CIRL on an alpha-latrotoxin affinity column and forms stable complexes with this receptor in vitro. Interaction of CIRL with a specific presynaptic neurotoxin and with a component of the docking-fusion machinery suggests its role in regulation of neurosecretion
— id: 7186, year: 1997, vol: 18, page: 925, stat: Journal Article,

The calcium-independent receptor of alpha-latrotoxin is not a neurexin
Krasnoperov VG; Beavis R; Chepurny OG; Little AR; Plotnikov AN; Petrenko AG
1996 Oct 23;227(3):868-875, Biochemical & biophysical research communications
alpha-Latrotoxin (alpha-LTx), a vertebrate neurotoxin isolated from Black Widow Spider venom, causes massive spontaneous neurotransmitter release. The molecular mechanism(s) by which the toxin exerts its effect is largely unknown. Here we report identification and purification of a novel membrane receptor with high affinity for alpha-LTx. Unlike neurexin Ia, a previously described high affinity alpha-LTx receptor, this novel protein binds alpha-LTx independently of Ca2+ presence and therefore may be a mediator of the calcium-independent stimulation of neurotransmitter release by alpha-latrotoxin. The major protein component of calcium-independent alpha-LTx receptors is a novel M(r) 120,000 protein which does not belong to the neurexin family. Among several tissues tested, the M(r) 120,000 protein was found only in brain
— id: 12513, year: 1996, vol: 227, page: 868, stat: Journal Article,

Structure and evolution of neurexophilin
Petrenko, AG; Ullrich, B; Missler, M; Krasnoperov, V; Rosahl, TW; Sudhof, TC
1996 JUL 15 ;16(14):4360-4369, Journal of neuroscience
Using affinity chromatography on immobilized Lu-latrotoxin, we have purified a novel 29 kDa protein, neurexophilin, in a complex with neurexin l alpha. Cloning revealed that rat and bovine neurexophilins are composed of N-terminal signal peptides, nonconserved N-terminal domains (20% identity over 80 residues), and highly homologous C-terminal sequences (85% identity over 169 residues). Analysis of genomic clones from mice identified two distinct neurexophilin genes, one of which is more homologous to rat neurexophilin and the other to bovine neurexophilin. The first neurexophilin gene is expressed abundantly in adult rat and mouse brain, whereas no mRNA corresponding to the second gene was detected in rodents despite its abundant expression in bovine brain, suggesting that rodents and cattle primarily express distinct neurexophilin genes. RNA blots and in situ hybridizations revealed that neurexophilin is expressed in adult rat brain at high levels only in a scattered subpopulation of neurons that probably represent inhibitory interneurons; by contrast, neurexins are expressed in all neurons. Neurexophilin contains a signal sequence and is N-glycosylated at multiple sites, suggesting that it is secreted and binds to the extracellular domain of neurexin l alpha. This hypothesis was confirmed by binding recombinant neurexophilin to the extracellular domains of neurexin Icr, Together our data suggest that neurexophilin constitutes a secreted glycoprotein that is synthesized in a subclass of neurons and may be a ligand for neurexins
— id: 52863, year: 1996, vol: 16, page: 4360, stat: Journal Article,

HIGH-AFFINITY BINDING OF ALPHA-LATROTOXIN TO RECOMBINANT NEUREXIN I-ALPHA
DAVLETOV, BA; KRASNOPEROV, V; HATA, Y; PETRENKO, AG; SUDHOF, TC
1995 OCT 13 ;270(41):23903-23905, Journal of biological chemistry
alpha-Latrotoxin is a potent neurotoxin from black widow spider venom that stimulates neurotransmitter release. alpha-Latrotoxin is thought to act by binding to a high affinity receptor on presynaptic nerve terminals. In previous studies, high affinity alpha-latrotoxin binding proteins were isolated and demonstrated to contain neurexin I alpha as a major component. Neurexin I alpha is a cell surface protein that exists in multiple differentially spliced isoforms and belongs to a large family of neuron-specific proteins. Using a series of neurexin I-IgG fusion proteins, we now show that recombinant neurexin I alpha binds alpha-latrotoxin directly with high affinity (K-d approximate to 4 nM). Binding of alpha-latrotoxin to recombinant neurexin I alpha is dependent on Ca2+ (EC(50) approximate to 30 mu M). Our data suggest that neurexin I alpha is a Ca2+-dependent high affinity receptor for alpha-latrotoxin
— id: 86702, year: 1995, vol: 270, page: 23903, stat: Journal Article,

Synaptotagmin: a calcium sensor on the synaptic vesicle surface
Brose N; Petrenko AG; Sudhof TC; Jahn R
1992 May 15;256(5059):1021-1025, Science
Neurons release neurotransmitters by calcium-dependent exocytosis of synaptic vesicles. However, the molecular steps transducing the calcium signal into membrane fusion are still an enigma. It is reported here that synaptotagmin, a highly conserved synaptic vesicle protein, binds calcium at physiological concentrations in a complex with negatively charged phospholipids. This binding is specific for calcium and involves the cytoplasmic domain of synaptotagmin. Calcium binding is dependent on the intact oligomeric structure of synaptotagmin (it is abolished by proteolytic cleavage at a single site). These results suggest that synaptotagmin acts as a cooperative calcium receptor in exocytosis
— id: 8194, year: 1992, vol: 256, page: 1021, stat: Journal Article,

Neurexins: synaptic cell surface proteins related to the alpha-latrotoxin receptor and laminin
Ushkaryov YA; Petrenko AG; Geppert M; Sudhof TC
1992 Jul 3;257(5066):50-56, Science
A family of highly polymorphic neuronal cell surface proteins, the neurexins, has been identified. At least two genes for neurexins exist. Each gene uses alternative promoters and multiple variably spliced exons to potentially generate more than a 100 different neurexin transcripts. The neurexins were discovered by the identification of one member of the family as the receptor for alpha-latrotoxin. This toxin is a component of the venom from black widow spiders; it binds to presynaptic nerve terminals and triggers massive neurotransmitter release. Neurexins contain single transmembrane regions and extracellular domains with repeated sequences similar to sequences in laminin A, slit, and agrin, proteins that have been implicated in axon guidance and synaptogenesis. An antibody to neurexin I showed highly concentrated immunoreactivity at the synapse. The polymorphic structure of the neurexins, their neural localization, and their sequence similarity to proteins associated with neurogenesis suggest a function as cell recognition molecules in the nerve terminal
— id: 8390, year: 1992, vol: 257, page: 50, stat: Journal Article,

Binding of synaptotagmin to the alpha-latrotoxin receptor implicates both in synaptic vesicle exocytosis
Petrenko AG; Perin MS; Davletov BA; Ushkaryov YA; Geppert M; Sudhof TC
1991 Sep 5;353(6339):65-68, Nature
A vertebrate neurotoxin, alpha-latrotoxin, from black widow spider venom causes synaptic vesicle exocytosis and neurotransmitter release from presynaptic nerve terminals. Although the mechanism of action of alpha-latrotoxin is not known, it does require binding of alpha-latrotoxin to a high-affinity receptor on the presynaptic plasma membrane. The alpha-latrotoxin receptor seems to be exclusively at the presynaptic plasmamembrane. Here we report that the alpha-latrotoxin receptor specifically binds to a synaptic vesicle protein, synaptotagmin, and modulates its phosphorylation. Synaptotagmin is a synaptic vesicle-specific membrane protein that binds negatively charged phospholipids and contains two copies of a putative Ca(2+)-binding domain from protein kinase C (the C2-domain), suggesting a regulatory role in synaptic vesicle fusion. Our findings suggest that a physiological role of the alpha-latrotoxin receptor may be the docking of synaptic vesicles at the active zone. The direct interaction of the alpha-latrotoxin receptor with a synaptic vesicle protein also suggests a mechanism of action for this toxin in causing neurotransmitter release
— id: 56395, year: 1991, vol: 353, page: 65, stat: Journal Article,

Isolation and properties of the alpha-latrotoxin receptor
Petrenko AG; Kovalenko VA; Shamotienko OG; Surkova IN; Tarasyuk TA; Ushkaryov YuA; Grishin EV
1990 Jun;9(6):2023-2027, EMBO journal
The receptor protein of alpha-latrotoxin (alpha LTx, a neurotoxin with 'pure' presynaptic action isolated from black widow spider venom), was solubilized by Triton X-100 from bovine brain membranes and purified by affinity chromatography on alpha LTx-Sepharose. The purified receptor preparation contained four major polypeptides of molecular masses 200 (alpha), 160 (alpha'), 79 (beta) and 43 (gamma) kd according to SDS electrophoresis with molecular ratio alpha 1 alpha' 1 beta 2 gamma 2. The alpha- and alpha'-subunits are glycoproteins binding to wheat germ lectin and can be separated under non-denaturing conditions by anion exchange chromatography. Purified to homogeneity, both of them, though differing in the carbohydrate composition, retain the alpha LTx-binding activity and give closely related peptide maps. Anti-alpha antibodies recognize the alpha'-subunit as well. These results suggest that alpha LTx receptor is present in purified preparations in two very close forms containing the alpha- or alpha'-subunit. Beta and gamma proteins do not specifically bind alpha LTx and their physiological role is unclear. They form a complex with solubilized alpha- and alpha'-subunits independently of alpha LTx presence. The receptor proteins were purified to homogeneity by high performance gel filtration in the presence of SDS, their amino acid composition was determined
— id: 56709, year: 1990, vol: 9, page: 2023, stat: Journal Article,