Antibodies to Obese/Leptin Receptor

M= Mouse; R=Rat; H=Human; Rb=Rabbit; G=goat; B=Bovine, MO=Monkey; P=pig; CT= near C-terminus; NT=near N-terminus; Internal=Middle of protein. EC=extracellular; CP=cytoplasmic domains *


Recombinant Leptin (Obese Protein) And Leptin Receptor Antibodies and Leptin ELISA Kit

Obesity, a common nutritional disorder, is associated with diabetes, hypertension, hyperlipidemia, cancer and many other health related problems. At least five genes, Obese (ob), diabetes (db), fat (fat), agouti yellow (Ay), and tubby (tub) have been linked to obesity. Recently, Ob genes (mouse and human) have been cloned. Obese gene encodes an adipocyte-tissue derived secreted Ob protein/Leptin (167 amino acid, ~16 kDa) that controls body weight homeostasis. Exogenous administration of recombinant Ob protein can reduce food intake and body weight. However, Ob protein had no effect in db/db mice suggesting a defect in leptin signaling mechanism. The Obese receptors (Ob-R) have now been cloned from mouse choroid plexus and it is expressed in several tissues including hypothalamus. The Ob-R has been shown to be a product of db gene that has long been thought to encode the receptor for a weight-controlling hormone. The Ob-R has at least 6 alternatively spliced forms with modifications at the amino and C-terminus (Fig 2). The Ob-R varies in length after Lysine889. The Ob-Ra represents the initially identified mouse Ob-R (short form, 894 AA). Ob-Rb displays ~78% homology to the human Ob-R (long form, 1165 AA). Expression of Ob-Rb and other forms have been detected in hypothalamus and other tissues. The soluble Ob-Re is found in adipose tissues, hypothalamus, heart, and testes. Ob-R is abnormally spliced in db/db mice and missing the cytoplasmic domain thought to be important for leptin signaling.

More recently, another variant of OBR, termed OB-RGRP (obese receptor gene related protein), has been identified that is distinct from the leptin receptor itself. OB-RGRP transcript contains the first two OBR gene 5'-untranslated exons, but then is alternatively spliced to two either leptin receptor or 131 aa protein OB-RGRP. The OB-RGRP is highly conserved in mouse, rat, human, yeast and C. elegans. OPB-RGRP is highly expressed in the hypothalamic regions that express the OBR mRNA. The OBR/B219, but not the OB-RGRP, is up-regulated in hypothalamus of ob/ob mice. OB-RGRP mRNA is also detected in heart, placenta, lung, liver, skeletal muscle, kidney, and pancreas. A new full-length cDNA encoding a new 131 aa protein, leptin receptor overlapping transcript-like 1 gene (LEPROTL1), that is highly homologous with OB-RGRP (~70% identity with OB-RGRP). LEPROTL1 is also widely expressed and has a similar JAK binding site (Pro46-Ile-Pro48) that is conserved in homologous proteins. LEPROTL1 protein is predicted to display 3 TM domains with an extracellualr N-terminus and intracellular C-terminus.

ADI provides mouse/human recombinant leptin expressed in E Coli (purity >95%) and made antibodies using whole protein. Purified leptin has low endotoxin level and shown to be biologically effective in reducing body weight, food consumption in ob/ob mice. A series of peptide derived antibodies to both Obese protein (AbOb1 and AbOb2), and Obese receptors are also available. These antibodies should prove to be useful in studying Leptin, Leptin-receptor interaction, and signaling and underlying defects in obese and diabetic mice and humans. Crossreactivity of Ob-R antibodies to mouse and human (see in table 1) and to various isoforms is based only upon sequence homology information and it needs to be experimentally confirmed. Control antigenic peptides are available to determine specificity of antibodies.

Ob-Ra   N886F887Q888K889 ~ RTDL (Mouse Ob-R)/Short Form
Ob-Rb   N886F887Q888K889 ~ PETFE ………..CDTLV (Human Ob-R)/Long Form
Ob-Rc   N886F887Q888K889 ~ VTV (Mouse Ob-R)
Ob-Rd   N886F887Q888K889 ~ DISFHEVFIFR (Mouse Ob-R)
Ob-Re   N886F887Q888K889 ~ GMCTVLFMD (Mouse Ob-R)/Soluble Form

Leptin is structurally related to cytokine family and it activates cytokine-like signal transduction by stimulating the JAK-STAT pathway via the OBRb, a member of IL-6 receptor family of class I cytokine receptors. Leptin binding to OBRb results in the activation of JAK2 and subsequent phosphorylation of specific tyrosines (Tyr985 and Tyr1138) located at the C-terminal, cytoplasmic region of OBRb. Phosphorylation of OBRb Tyr1138 recruits the SH2 domain containing STAT3, its autophosphorylation, translocation to the nucleus, and modulation of gene transcription, most notably induction of suppressor of cytokine signaling 3 gene (SOCS3 or CIS3). SOCS3 inhibits leptin signaling. SOCS3 have been reported to be elevated in some obese animals. Tyr985 phosphorylation of OBRb recruits the SH2 domain containing protein-tyrosine phosphatase SHP-2, it's binding to GRB2, and subsequent activation of ERK, a group of ser/thr kinases involved in the regulation of gene transcription. Therefore, OBRb Tyr phosphorylation plays in critical role in leptin signaling.