ERP ( EPO receptor peptide )
alright guys, theres this new peptide thats out, and i was wondering if any of you knew about it. ERP ( EPO receptor peptide ) i have not been able to find too much info on it. does any one know how it compares to vit.E? i know that it attaches to a different thing than EPO does. It is MUCH cheaper and the hopes for this being a good replacement along with being undetectable are very good looking so far.
here's a bit of info:
Activation of erythropoietin (EPO) receptor (EPOR) by a small peptide (ERP) was reported previously. ERP binds to a different receptor site than EPO, and binding of ERP does not change the dissociation constant and maximal binding for EPO binding to the receptor. The extracellular binding site for ERP is now characterized. The site is located in the membrane proximal, extracellular part of the receptor. ERP binds to a region on the EPOR that contains the same sequence as ERP. It is speculated that ERP binds to its identical sequence on EPOR, as ERP self-interacts. ERP is specific for EPOR and associates noncovalently with EPOR in a ratio 1:1. Peptide binding to the receptor results in receptor-mediated cellular proliferation, intracellular signaling, and erythroid colony-forming unit formation in bone marrow cells. The activity is comparable to that of EPO. Recognition of such receptor sites represents a new and important concept in receptor function.
Erythropoietin (EPO) is a glycoprotein hormone that regulates the proliferation, differentiation, and maturation of erythroid cells. Its specific receptor, EPO receptor (EPOR), is expressed on the surface of erythroid progenitor cells and is a member of the class 1 cytokine receptor superfamily that includes the interleukins, human growth hormone, granulocyte colony-stimulating factor, and prolactin (6,7). A WSXWS motif as well as cysteine residues are well conserved in cytokine receptors (2,7). (Note, only the extracellular domains are shown in all of the following figures). The WSXWS motif is located away from the binding interfaces, although mutations in this area prevent binding of EPO (2). In EPOR, disulfide bonds are present between the conserved cysteines—between Cys28 and Cys38 and between Cys67 and Cys83 (2). There is only one other Cys residue in EPOR (2). Cytokine receptors also have conserved b-strand portions (2). The numerous b-strands in the EPOR are evident in the secondary structure of the protein.
EPOR consists of an extracellular ligand-binding domain, a short single transmembrane domain, and a cytoplasmic domain that lacks a kinase region (4). Signaling occurs through the JAK/STAT pathway, where ligand-induced sequential receptor homodimerization has been proposed to promote stable association of JAK2 and phosphorylation of JAK2, EPOR, and STAT5 (4).
Receptor dimer orientation affects EPOR activation. EPO binding protein (EBP) consists of residues 1 to 225 of human EPOR (4). Each EBP monomer consists of two FBN-III folds, connected at an approximate right angle, as in other cytokine receptors (4). However, the native EBP unexpectedly forms a cross-shaped dimer (4). N-Ctermini SCRIPT! In the figure, the amino 5’ end of each monomer is shown in blue. The carboxyl 3’ end, shown in red, is the membrane-proximal end. Each monomer points in opposite directions, with the C-terminal ends aligned toward the membrane with a rotation of 135º, or a distance of 73 Å, between them (4,6). In the unliganded self-dimer, this extracellular configuration holds the intracellular regions of the monomers far enough apart such that autophosphorylation of JAK2 cannot occur (4,6). Ligand binding causes a conformational change that brings the extracellular membrane-proximal domains within 39 Å of each other, allowing the interaction of the intracellular domains so that they become substrates for phosphorylation by two JAK2 molecules (4,6). Thus, EPOR exist as unliganded dimers on the cell surface (4). The binding of EPO triggers a switch between a self-associated, inactive conformation and an active, ligand-bound conformation (4).
The three key EPO binding residues, Phe93, Phe205, and Met150, form a hydrophobic core (4). Residues surrounding the hydrophobic core include Glu34, Ser91, His114, Asn116, Ser152, His153, Arg155, Glu176, Arg178, and Glu202 (4).
The cytoplasmic domain of the EPOR can be divided into two major regions. Roughly half of the cytoplasmic domain, the part lying nearest the plasma membrane, is required for generating the signals for proliferation and differentiation (7). The remaining half is not required for this signaling, and, conversely, it acts to dampen the signals (7). The tyrosine kinase JAK2 associates with the region near the plasma membrane, undergoes autophosphorylation, and phosphorylates the EPOR and the transcription factor STAT5 (7). Human EPOR has eight tyrosine residues in its cytoplasmic domain (3). wtEPOR DIAGRAM! Among them, both the first and the second tyrosine residues (Tyr344 and Tyr402) are required for STAT5 activation (3). The activated STAT5 then translocates to the nucleus, recognizes a specific base sequence in the promoter region of its target gene, and initiates transcription (7). EPORsignaling DIAGRAM! Deficiencies or mutations in the proteins involved in this signaling pathway may lead to abnormal erythropoiesis.
A peptide, designated EPOR peptide (ERP), with an identical sequence to a site on the EPOR, activates receptor signaling in the absence of EPO and can also act in synergy with EPO (5). The ERP sequence (amino acids 194-216 of human EPOR) is contained in the same extracellular domain of EPOR as that known to participate in dimerization of activated receptor chains (5). ERP binds to its identical sequence in the membrane-proximal region on EPOR, between amino acids 174-223 (5).
The binding sites for EPO and ERP on the EPOR are different, with the ERP site being more membrane-proximal than EPO (5). (In the figure, the EPO binding site is shown in yellow and the ERP binding site in green). ERP binding to EPOR results in receptor-mediated signal transduction and cell proliferation (5). ERP does not affect the binding (either in terms of number of binding sites or of affinity) of the natural ligand to the receptor (5). It is suggested that the ERP binding site on EPOR also has a functional role in the activation of EPOR in the presence of EPO because this site is localized in the dimerization region of the receptor (5).
Expression of EPO receptors in several nonhematopoietic cell types has been associated with the discovery of novel physiologic effects of EPO in such tissues (1). For instance, in the developing heart, EPO and EPOR function is required for normal cardiac morphogenesis (1). In the female reproductive tract, a paracrine EPO-EPOR system has been implicated in estrogen-dependent cyclical uterine angiogenesis (1). In the central nervous system, expression of EPO receptors in neurons and brain capillaries is associated with a neuroprotective effect for EPO during ischemia-induced injury in vivo (1). Arcasoy et al. report that functional, nonhematopoietic EPOR expression can also be associated with breast cancer. In many primary breast tumors analyzed by the researchers, there was coexpression of EPO and EPOR protein (1). EPO-EPOR antagonists significantly delayed tumor growth (1). This suggests a functional significance for EPO and EPOR expression in cancer cells with respect to cancer cell proliferation and that inhibitors of EPOR signaling may exhibit significant anti-tumor activity in vivo (1).
Erythropoietin mimetic peptides and the future
Dana L. Johnson and Linda K. Jolliffe
R. W. Johnson Pharmaceutical Research Institute, Raritan, NJ, USA
The primary regulator of the growth and survival of erythroid progenitors, which mature into red blood cells, is the glycoprotein hormone erythropoietin (Epo) . Epo exerts this effect by specifically interacting with a receptor present on the surface of progenitor cells which leads to receptor activation and initiation of an intracellular signal cascade. Over the last 10 years, the availability of recombinant Epo has led to its widespread use in stimulating red cell synthesis for the treatment of severe anaemia associated with acute and chronic disease . In both chronic renal failure and cancer settings, severe anaemia and associated fatigue have a significant impact on the patient's quality of life. There have been a number of controlled trials in which patients receiving Epo demonstrated a significant improvement in quality of life scores and functional capacity.
While highly safe and efficacious, a desirable improvement sought for Epo therapy is in the mode of drug delivery . The cost and inconvenience associated with chronic parenteral administration of Epo and other protein therapeutics have led a number of investigators to seek ways to deliver proteins orally, transdermally and by inhalation. However, the size and intrinsic lability of proteins has hindered progress along these lines. A second and perhaps even more difficult strategy to obtain orally administered agents has been to discover small molecule drugs that retain the full agonist activity of the larger protein molecules . The motivation for attempting such a high-risk research strategy for Epo has been fueled by several potential benefits. In addition to the contemporary uses of Epo, an oral agent would potentially extend to therapeutic applications in less severe anaemia conditions associated with rheumatoid arthritis and other chronic inflammatory disorders. To this end, we and others have been pursuing small molecule mimetics of Epo and other protein hormones and cytokines. In the 10 years since Epo was first approved for use in man, we have not yet been successful in delivering an orally active Epo mimetic. However, a number of key steps have been reached in the search for small molecule agonists of the Epo receptor and a great deal of knowledge concerning Epo receptor structural biology has emerged from these efforts . Peptide mimics of Epo
The Epo receptor (EPOR) is a member of a superfamily of cytokine receptors which includes receptors for growth hormone (GH), granulocyte-colony stimulating factor (G-CSF), thrombopoietin (TPO) and others .
The molecular arrangement of a prototypic member of this group would possess an extracellular ligand-binding domain, a single-pass transmembrane region and an intracellular signalling domain that interacts with members of a signalling cascade .
The receptors themselves have no intrinsic kinase activity.
In the case of EPOR, the mechanism for activation involves the binding and homodimerization of two receptor monomers by a single Epo molecule resulting in a 2 : 1 receptor–hormone assembly. The dimerization of the receptor leads to cell signalling via the activation of Janus Kinase 2 molecules associated with the cytoplasmic domain .
The initial bias against finding small molecule mimetics of Epo was founded in the prevailing thought that the large surface area contacted by a glycoprotein the size of Epo (165 amino acids) to the dimeric receptor complex would be impossible to replicate with a much smaller molecular entity. However, both structural and mutagenesis studies with a related family member, GH receptor, showed that only a small subset of the ligand–receptor contacts accounted for the bulk of the binding energy [9,10]. The residues most influential in binding have been termed a ‘functional epitope’ region, or a minimal area most important for ligand binding to the receptor.
Through combinatorial peptide screening techniques using phage display technology, we were able to isolate a novel 20 amino acid peptide mimetic (Epo Mimetic Peptide, EMP1—Table 1) of EPO and subsequently to determine the structure as an EMP1–EPOR complex [11,12]. The peptide–receptor assembly consisted of two peptides bound to two receptor monomers in a 2 : 2 ratio and in an almost perfectly symmetrical arrangement. The peptide has no sequence homology to that of Epo and was found to possess Epo mimetic action both in vitro and in animals albeit with less specific activity than that of Epo itself. Interestingly, we also found that the minimal active peptide sequence consists of only a 13 amino acid complement of the original 20 amino acid EMP1 sequence indicating that molecules even smaller than EMP1 can serve as receptor agonists .
To our excitement, the receptor contact residues in the dimeric peptide–receptor assembly overlapped perfectly with the key ‘hotspots’ of the GH/GH receptor binding assembly, consistent with the notion that only a small complement of receptor molecules are involved in binding and subsequent activation of cytokine superfamily receptors. Taken together, these data supply the foundation for the premise that such molecules as Epo and GH can be mimicked by a small molecule .
To further probe this concept, we have shown that preparation of peptide dimers using either defined chemical linkers  or larger polymeric PEG linkers  resulted in Epo mimetic molecules with greater specific activity. Significantly, it is also possible to convert inactive peptides that retain binding ability into weak agonists via ligand dimerization . This suggests that binding alone can be exploited to provide the basis for receptor activation. However, not all inactive peptide sequences with retained binding ability could be converted into agonists, suggesting a conformational requirement that must also be satisfied before receptor activation can occur .
The discovery of a small peptidic molecule with the full agonist activity of Epo provided the impetus for others to reconsider the potential for the discovery of peptides and nonpeptidic mimetics of Epo and other cytokines. A number of other reports of peptide agonists for both the Epo [16,17] and TPO  receptors have subsequently been published.
The EPO mimetic peptide family reported in  is represented by a cyclic 18 amino acid peptide, termed ERB1–7, which was discovered in a fashion similar to EMP1 (Table 1
its supposed to raise it just like EPO. its supposed to be in comparison as t4 is to t3. if that helps any.