Identification of a human LNX protein containing multiple PDZ domains

Recently PDZ domains have been recognized as crucial organizers of protein complexes at the plasma membrane. Here we report the cloning of a novel 3.7-kb cDNA LNX from a human fetal brain cDNA library. The deduced amino acid sequence shares about 88% identity with the p70 form of Lnx, which is the mouse ligand of Numb protein X. Motif analysis reveals five protein-interaction modules conservative to those in the Lnx protein, including four PDZ domains and a NPXY motif for binding of the Numb PTB domain. Northern blot analysis shows that the length of the transcript in brain is distinct from those in other tissues. By radiation hybrid mapping, we localize the LNX gene to human chromosome 4q12 between marker D4S1577 and marker D4S1594. We predict that LNX may be important for the organization of signaling complexes in Numb-involved pathways or pathways regulated by other PTB-containing proteins.