Anti-LMTK2 monoclonal antibody, clone 576333

Background: The membrane anchored kinase, LMTK2, is a serine/threonine kinase predominantly localized to endosomal compartments. LMTK2 has been shown to be involved in the trafficking of the CFTR ion channel, the androgen receptor, as well as modulating neurodegeneration. As a membrane anchored protein, LMTK2 must be exported from the ER, yet the mechanisms whereby LMTK2 is sequestered within the ER for efficient export are unknown. Methods: Sequence analysis of the carboxyl tail of LMTK2 revealed a putative di-acidic ER export motif. Site-directed mutagenesis was utilized to ablate this potential motif. Subcellular fractionation, immunofluorescence microscopy, and transferrin recycling assays were used to determine the consequence of mutating LMTK2's exportmotif. Results: Mutation of the di-acidic export motif led to ER retention of LMTK2, and an increase in protein half-life and a concomitant loss of LMTK2 from its appropriate terminal destination. Loss of LMTK2 from endosomal compartments by preventing its release from the ER is linked to a reduction in transferrin recycling. Conclusions: We have identified a di-acidic ER export motif within the carboxyl tail of the membrane anchored kinase LMTK2. This sequence is used by LMTK2 for its efficient export from the ER.

Nixon A, Jia Y, White C, Bradbury NA. Determination of the membrane topology of lemur tyrosine kinase 2 (LMTK2) by fluorescence protease protection. Am J Physiol Cell Physiol 304: C164-C169, 2013. First published October 31, 2012; doi:10.1152/ajpcell.00288.2012.-Lemur tyrosine kinase 2 (LMTK2) is a novel membrane-anchored kinase reported to be involved in several normal and pathophysiological conditions, including endosomal membrane recycling, prostate cancer, and neurodegeneration. In this study, we have investigated the topology and orientation of LMTK2 within cellular membranes utilizing fluorescence protease protection. Appending the green fluorescent protein to either the amino or carboxyl terminus of LMTK2, we were able to determine which side of intracellular membrane these regions were located. Our results indicate that LMTK2 is an integral membrane protein in which both the amino and carboxyl termini are exposed to the cytoplasm. Moreover, this topology places the kinase active site within the cytoplasm.