A Domain organisation of Lselectin' All the selectins have similar extracellular domains' E and Psel

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(A) Domain organisation of L-selectin. All the
selectins have similar extracellular domains. E-
and P-selectin have 6 and 9 sequence consensus
repeats respectively, whereas L-selectin has only
two. One possible reason for this difference is
that L-selectin is anchored on microvilli and
this presents it more efficiently to counter
ligands, facilitating engagement during tethering
and rolling. L-selectin is the only selectin that
carries a defined extracellular cleavage site
that is close to the cell membrane. Leukocyte
stimulation can often lead to rapid cleavage at
this site.(B) Schematic diagram of L-selectin
cytoplasmic tail (R-356 to Y-372) and interaction
with the ERM proteins. Highlighted in red are the
residues R-357 and K-362, which have been shown
to contribute binding to N-terminal moesin.
Mutagenesis of either R357 or K362 to an alanine
results in (i) reduced PMA-induced shedding (ii)
reduced localisation to microvilli and (iii)
reduced tethering efficiency.