STRUCTURAL REQUIREMENTS FOR INDUCIBLE SHEDDING OF THE P55 TUMOR-NECROSIS-FACTOR RECEPTOR

Induced shedding of the p55 tumor necrosis factor receptor (p55-R) was previously shown 60 be independent of the amino acid sequence propert ies of the intracellular domain of this receptor. We now find it also independent of the sequence properties of the transmembrane domain and of the cysteine-rich region that constitutes most of the extracellula r domain of the receptor. The shedding is shown to depend solely on th e sequence properties of a small region within the spacer that Links t he cysteine-rich region in the extracellular domain to the transmembra ne domain. Detailed tests of effects of mutations in the spacer on the shedding indicate that the process is independent of the amino acid s ide-chain identity in this region except for a limited dependence on t he identity of 1 residue (Val-173), located downstream to the putative major cleavage site of the receptor. It is strongly affected, however , by some mutations that seem to change the conformation of the spacer region. These findings suggest that a short amino acid sequence in th e p55-R is essential and sufficient for its shedding and that the shed ding is mediated either by a protease with limited sequence specificit y or by several different proteases that recognize different amino aci d sequences, yet it strictly depends on some conformational features o f the cleavage region in the receptor.