LRIG3 (leucine-rich repeats and Ig-like domains-3) is a 140 kD type I transmembrane glycoprotein member of the mammalian LRIG glycoprotein family. This family contains three members who share 45-50% amino acid (aa) identity. 1 All members contain at least fifteen LRRs, accompanied by two flanking cysteine-rich regions, and three C2-type Ig-like domains in their extracellular domains (ECD). 1 LRIG3 mRNA is widely expressed, with highest levels in stomach, skin, thyroid and small intestine. 1 Human LRIG3 is synthesized as an 1120 amino acid (aa) precursor. It contains a 24 aa signal sequence, a 786 aa ECD, a 21 aa transmembrane sequence, and a 289 aa intracellular region. One splice variant exists that has a 19 aa substitution for the first 79 aa of the standard (or long) form. This substitution appears to encode an alternate signal sequence, resulting in a mature protein that lacks the first and part of the second LRR. LRIG1, a related family member, is known to bind the EGF family receptors ErbB1-4, via either its LRR or Ig-like domains. It also binds the ubiquitin ligase, c-Cbl, and promotes ubiquitination, internalization and destruction of these receptors. 2, 3 It is not known whether LRIG3 performs similar functions. Within the cell, LRIG3 is expressed in the perinuclear region as well as on the cell surface. Perinuclear location of LRIG3 in grade III and IV astrocytic tumors has been associated with better patient survival. 4 Human LRIG3 ECD shows 91%, 92%, 95% and 98% aa identity with mouse, rat, bovine and canine LRIG3 ECD, respectively.
Source: Human CD33 Signal peptide (Met 1-Ala 16), Human LRIG-3 (Asp 28-Thr 807), HHHHHH; A DNA sequence encoding the extracellular domain of human LRIG-3 (Asp 28-Thr 807; Accession # Q6UXM1) (Cark, H.F. et al, 2003 Genome Res. 13 (10), 2265-2270) was fused to the signal peptide of human CD-33 at the N-terminus and to a 6 x histidine tag at the C-terminus. The chimeric protein was expressed in a mouse myeloma cell line, NS0.
Molecular Mass: Based on N-terminal amino acid sequencing, the mature recombinant human LRIG-3 starts at Asp 28 and has a calculated molecular mass of approximately 87.1kD. As a result of glycosylation, the recombinant protein migrates as an approximately 105-115kD protein in SDS-PAGE under reducing conditions.
Endotoxin Level: < 1.0 EU per 1 μg of the protein as determined by the LAL method.
Activity: Measured by its ability to inhibit proliferation of the human cervical epithelium cancer cell line, Hela (Goldoni, S. et. al. 2007, Oncogene, 26:368-81). The ED50 for this effect is typically 1.5-6ug/ml.
Reconstitution: It is recommended that sterile phosphate-buffered saline be added to the vial to prepare a working stock solution of no less than 100ug/ml. The carrier-free protein should be used immediately upon reconstitution to avoid losses in activity due to non-specific binding to the inside surface of the vial. For long term storage as a dilute solution, a carrier protein (e.g. 0.1% HSA or BSA) should be added to the vial.
Storage: Lyophilized samples are stable for up to twelve months from date of receipt at -20°C. Upon reconstitution, this protein, in the presence of a carrier protein, can be stored under sterile conditions at 2-8°C for one month or at -20°C in a manual defrost freezer for three months without detectable loss of activity. Avoid repeated freeze-thaw cycles.
