Probing the H-protein-induced Conformational Change and the Function of the N-terminal Region of Escherichia coliT-protein of the Glycine Cleavage System by Limited Proteolysis
T-protein, a component of the glycine cleavage system, catalyzes a tetrahydrofolate-dependent reaction. Previously, we reported a conformational change of Escherichia coli T-protein upon interacting with E. coli H-protein (EH), showing an important role for the N-terminal region of the T-protein in...
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Published in | The Journal of biological chemistry Vol. 278; no. 12; pp. 10067 - 10072 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
American Society for Biochemistry and Molecular Biology
01.03.2003
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Online Access | Get full text |
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Summary: | T-protein, a component of the glycine cleavage system, catalyzes a tetrahydrofolate-dependent reaction. Previously, we reported
a conformational change of Escherichia coli T-protein upon interacting with E. coli H-protein (EH), showing an important role for the N-terminal region of the T-protein in the interaction. To further investigate
the T-protein catalysis, the wild type (ET) and mutants were subjected to limited proteolysis. ET was favorably cleaved at
Lys 81 , Lys 154 , Lys 288 , and Lys 360 by lysylendopeptidase and the cleavages at Lys 81 and Lys 288 were strongly prevented by EH. Although ET was highly resistant to trypsinolysis, the mutant with an N-terminal 7-residue
deletion (ETÎ7) was quite susceptible and instantly cleaved at Arg 16 accompanied by the rapid degradation of the resulting C-terminal fragment, indicating that the cleavage at Arg 16 is the trigger for the C-terminal fragmentation. EH showed no protection from the N-terminal cleavage, although substantial
protection from the C-terminal fragmentation was observed. The replacement of Leu 6 of ET with alanine resulted in a similar sensitivity to trypsin as ETÎ7. These results suggest that the N-terminal region
of ET functions as a molecular âhaspâ to hold ET in the compact form required for the proper association with EH. Leu 6 seems to play a central role in the hasp function. Interestingly, Lys 360 of ET was susceptible to proteolysis even after the stabilization of the entire molecule of ET by EH, indicating its location
at the surface of the ET-EH complex. Together with the buried position of Lys 81 in the complex and previous results on folate binding sites, these results suggest the formation of a folate-binding cavity
via the interaction of ET with EH. The polyglutamyl tail of the folate substrate may be inserted into the bosom of the cavity
leaving the pteridine ring near the entrance of the cavity in the context of the catalytic reaction. |
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ISSN: | 0021-9258 1083-351X |
DOI: | 10.1074/jbc.M210853200 |