The spleen protein-tyrosine kinase TPK-IIB is highly similar to the catalytic domain of p72syk.
TPK-IIB is a protein kinase that is predominant in the cytosol of spleen and is characterized by a high specific activity toward acidic peptide substrates and a low auto-phosphorylation activity. A prominent 52-kDa component purifies with the kinase [Marin, O., Donella-Deana, A., Brunati, A. M., Fischer, S. & Pinna, L. A. (1991) J. Biol. Chem. 266, 17798-17803]. Here we demonstrate that the 52-kDa protein displays sequence identity with the Miller-Dieker lissencephaly protein (LIS 1). The protein is not related to any known protein kinase and lacks an ATP-binding motif. The ATP binding and phosphotransferase activities of TPK-IIB can be fully accounted for by a minor 38-kDa protein band (p38/TPK-IIB) which can be separated from the 52-kDa protein by Mono-Q/FPLC in the presence of EDTA. Sequence analysis of p38/TPK-IIB reveals a high level of similarity, if not identity, with the catalytic domain of p72syk, a protein-tyrosine kinase implicated in the activation of hematopoietic cells. Antibodies raised against the catalytic domain of p72syk, but not antibodies raised against its N-terminal segment, cross-react with p38/TPK-IIB. The peptide substrate specificity of p72syk is almost identical to that of p38/TPK-IIB, which also supports the classification of TPK-IIB as a close relative (possibly a proteolytic or alternative spliced form) of p72syk. p38/TPK-IIB, however, exhibits a specific activity which is sixfold higher than that of p72syk and appears to be 50-fold more sensitive to inhibition by heparin. Thus, the observation that Ca(2+)-dependent degradation of p72syk by particulate fraction of rat spleen is accompanied by increased catalytic activity and increased sensitivity to heparin would be consistent with the possibility that hyperactive p38/TPK-IIB might be proteolytically generated from p72syk in response to an increase of intracellular Ca2+.
Brunati
A M
AM
Dipartimento di Chimica Biologica, Università di Padova, Italy.
James
P
P
Guerra
B
B
Ruzzene
M
M
Donella-Deana
A
A
Pinna
L A
LA
D000345:Affinity Labels / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000494:pharmacology; D002384:Catalysis; D002845:Chromatography; D016208:Databases, Factual; D004591:Electrophoresis, Polyacrylamide Gel; D004792:Enzyme Precursors / Q000737:chemistry* / Q000378:metabolism; D006493:Heparin / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D007700:Kinetics; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D051381:Rats; D017421:Sequence Analysis; D013154:Spleen / Q000201:enzymology*; D000072377:Syk Kinase; D014357:Trypsin / Q000378:metabolism
D000345:Affinity Labels; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D010446:Peptide Fragments; D006493:Heparin; C101848:tyrosine protein kinase IIB; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; C000606898:Syk protein, rat; D014357:Trypsin; D002118:Calcium