title: PTB domain-directed substrate targeting in a tyrosine kinase from the unicellular choanoflagellate Monosiga brevicollis.
abstract: Choanoflagellates are considered to be the closest living unicellular relatives of metazoans. The genome of the choanoflagellate Monosiga brevicollis contains a surprisingly high number and diversity of tyrosine kinases, tyrosine phosphatases, and phosphotyrosine-binding domains. Many of the tyrosine kinases possess combinations of domains that have not been observed in any multicellular organism. The role of these protein interaction domains in M. brevicollis kinase signaling is not clear. Here, we have carried out a biochemical characterization of Monosiga HMTK1, a protein containing a putative PTB domain linked to a tyrosine kinase catalytic domain. We cloned, expressed, and purified HMTK1, and we demonstrated that it possesses tyrosine kinase activity. We used immobilized peptide arrays to define a preferred ligand for the third PTB domain of HMTK1. Peptide sequences containing this ligand sequence are phosphorylated efficiently by recombinant HMTK1, suggesting that the PTB domain of HMTK1 has a role in substrate recognition analogous to the SH2 and SH3 domains of mammalian Src family kinases. We suggest that the substrate recruitment function of the noncatalytic domains of tyrosine kinases arose before their roles in autoinhibition.
authors.affiliation: Department of Physiology and Biophysics, School of Medicine, Stony Brook University, Stony Brook, New York, United States of America.
authors.forename: Victoria
authors.initials: V
authors.lastname: Prieto-Echagüe
authors.forename: Perry M
authors.initials: PM
authors.lastname: Chan
authors.forename: Barbara P
authors.initials: BP
authors.lastname: Craddock
authors.forename: Edward
authors.initials: E
authors.lastname: Manser
authors.forename: W Todd
authors.initials: WT
authors.lastname: Miller
mesh_terms: D000595:Amino Acid Sequence; D056897:Choanoflagellata / Q000166:cytology* / Q000201:enzymology*; D008024:Ligands; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011505:Protein-Tyrosine Kinases / Q000737:chemistry* / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D008024:Ligands; D010455:Peptides; D011505:Protein-Tyrosine Kinases