C-terminal Src kinase-homologous kinase (CHK), a unique inhibitor inactivating multiple active conformations of Src family tyrosine kinases.
The Src family of protein kinases (SFKs) mediates mitogenic signal transduction, and constitutive SFK activation is associated with tumorigenesis. To prevent constitutive SFK activation, the catalytic activity of SFKs in normal mammalian cells is suppressed mainly by two inhibitors called C-terminal Src kinase (CSK) and CSK-homologous kinase (CHK), which inactivate SFKs by phosphorylating a consensus tyrosine near the C terminus of SFKs (Y(T)). The phosphorylated Y(T) intramolecularly binds to the SH2 domain of SFKs. This interaction, known as pY(T)/SH2 interaction, together with binding between the SH2 kinase linker and the SH3 domain of SFKs (linker/SH3 interaction) stabilizes SFKs in a "closed" inactive conformation. We previously discovered an alternative mechanism CHK employs to inhibit SFKs. This mechanism, referred to as the non-catalytic inhibitory mechanism, involves tight binding of CHK to SFKs; the binding alone is sufficient to inhibit SFKs. Herein, we constructed multiple active conformations of an SFK member, Hck, by systematically disrupting the two inhibitory interactions. We found that CHK employs the non-catalytic mechanism to inactivate these active conformations of Hck. However, CHK does not bind Hck when it adopts the inactive conformation in which both inhibitory interactions are intact. These data indicate that binding of CHK to SFKs via the non-catalytic mechanism is governed by the conformations of SFKs. Although CSK is also an inhibitor of SFKs, it does not inhibit SFKs by a similar non-catalytic mechanism. Thus, the non-catalytic inhibitory mechanism is a unique property of CHK that allows it to down-regulate multiple active conformations of SFKs.
Chong
Yuh-Ping
YP
Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria 3010, Australia.
Chan
Andrew S
AS
Chan
Khai-Chew
KC
Williamson
Nicholas A
NA
Lerner
Edwina C
EC
Smithgall
Thomas E
TE
Bjorge
Jeffrey D
JD
Fujita
Donald J
DJ
Purcell
Anthony W
AW
Scholz
Glen
G
Mulhern
Terrence D
TD
Cheng
Heung-Chin
HC
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002384:Catalysis; D002460:Cell Line; D015536:Down-Regulation; D004789:Enzyme Activation; D006801:Humans; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D011487:Protein Conformation; D018411:Spodoptera; D019061:src-Family Kinases / Q000145:classification / Q000235:genetics / Q000378:metabolism*
D019061:src-Family Kinases