Determination of the molecular reach of the protein tyrosine phosphatase SHP-1.
Clemens L., Kutuzov M., Bayer KV., Goyette J., Allard J., Dushek O.
Immune receptors signal by recruiting (or tethering) enzymes to their cytoplasmic tails to catalyse reactions on substrates within reach. This is the case for the phosphatase SHP-1 that, upon tethering to inhibitory receptors, dephosphorylates diverse substrates to control T cell activation. Precisely how tethering regulates SHP-1 activity is incompletely understood. Here, we measure binding, catalysis, and molecular reach for tethered SHP-1 reactions. We determine the molecular reach of SHP-1 to be 13.0 nm, which is longer than the estimate from the allosterically active structure (5.3 nm), suggesting that SHP-1 can achieve a longer reach by exploring multiple active conformations. Using modelling, we show that when uniformly distributed, receptor-SHP-1 complexes can only reach 15% of substrates but this increases to 90% when they are co-clustered. When within reach, we show that membrane recruitment increases the activity of SHP-1 by a 1000-fold increase in local concentration. The work highlights how molecular reach regulates the activity of membrane-recruited SHP-1 with insights applicable to other membrane-tethered reactions.