Tyrosine phosphorylation of extracellular proteins is observed in cell cultures and in vivo, but
little is known about the functional roles of tyrosine phosphorylation of extracellular proteins.
Vertebrate lonesome kinase (VLK) is a broadly expressed secretory pathway tyrosine kinase
present in platelet α-granules. It is released from platelets upon activation and
phosphorylates substrates extracellularly. Its role in platelet function, however, has not been
previously studied. In human platelets, we identified phosphorylated tyrosines mapped to …

Tyrosine phosphorylation of proteins secreted into the extracellular space has been
observed in cell cultures and in vivo, yet little is known about the role that phosphorylation of
extracellular proteins serves in modulating cell function. An important reason for the gap in
our knowledge of the functional significance of extracellular protein phosphorylation has
been the delay in identifying extracellular kinases. Within the last decade, however,
bioinformatic strategies to identify kinases with signal peptides, coupled with biochemical …