Differential binding of mLin-7 to the chimeric
receptors. (A) Schematic representation of the NGFR/P75 chimeric
receptor constructs. Amino acids 1–306 of the NGFR/P75 (truncated
after the transmembrane domain) were fused to the carboxyl-terminal
amino acids of LET-23 (shown in single letter code) to form the
P75t-Let23WT construct. The P75t-Let23MUT construct deletes the final
amino acid in the LET-23 carboxyl terminus, destroying the mLin-7 PDZ
domain ligand. (B) HEK293 cells were transfected with plasmids as
follows: lanes A, pRK5Myc-mLin-7 plus pP75t-Let23WT; lanes B,
pRK5Myc-mLin-7 plus pP75t-Let23MUT; lanes C, pRK5Myc-mLin-7 plus
pcDNA-3HA-mLin-2. Forty-eight hours after transfection, cells were
surface biotinylated, and then lysates were collected for
immunoprecipitation with anti-P75 or anti-HA antibodies, as indicated.
Precipitated proteins were separated by 10% SDS-PAGE, transferred to
nitrocellulose, and the membrane was probed with avidin-HRP (to detect
surface biotinylated P75t-Let23), anti-HA, or anti-Myc antibodies. The
input lanes contain approximately one-tenth the amount of HEK293 lysate
used in the precipitation experiments. The arrows indicate the relevant
bands on the immunoblots. Relative molecular weight is
shown to the right in kilodaltons.