Fig. 7. Steric penalty to binding and catalysis by short tethers.

(A) Shorter cytoplasmic tails (tethers) result in decreased k_on for binding and ${\mathit{k}}_{\text{cat}}^{*}(\text{tethered})$ for catalysis as a result of steric hindrance (indicated by thickness of black arrow). (B) Histograms of the contour length (number of amino acids × 0.3 nm per amino acid) to phosphotyrosine residues on inhibitory receptors (ITIM/ITSM; mean length of 21.2 nm, red histogram) and activatory receptors (ITAM/ITTM/YxxM; mean length of 11.3 nm, green histogram) for human receptors. Most inhibitory receptor tails are longer than PEG28 where steric penalties are lower, whereas most activatory receptor tails are shorter than PEG28 where steric penalties are higher.