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Dephosphorylation of synthetic phosphopeptides by protein phosphatase-T, a phosphothreonyl protein phosphatase.

1982; Elsevier BV; Volume: 257; Issue: 15 Linguagem: Inglês

10.1016/s0021-9258(18)34157-7

1083-351X

Arianna Donella Deana, Fernando Marchiori, Flavio Meggio, Lorenzo A. Pinna,

Mitochondrial Function and Pathology

The synthetic phosphohexapeptides Arg-Arg-Ala-Thr(32P)-Val-Ala and Arg-Arg-Ala-Ser(32P)-Val-Ala, phosphorylated by the CAMP-dependent protein kinase and differing only in the nature of the phosphorylated residue, have been used as substrates of a partially purified rat liver protein phosphatase-T, distinct from the multifunctional protein phosphatase-1.While the phosphothreonyl hexapeptide is readily dephosphorylated ( e x h i b i t i n g a K,,, = 15 p ~) , the phosphoseryl one is almost unaffected.Such a behavior is not shared by protein phosphatase-1, calf intestine alkaline phosphatase, and potato acid phosphatase, all of which are more active on the phosphoseryl hexapeptide.The NHz-terminal basic residues critical for CAMPdependent phosphorylation are not required in the dephosphorylation reaction, as both Arg can be removed without impairing the efficiency of protein phosphatase-T toward the phosphothreonyl peptide.On the other hand, the replacement o f 2 Pro for the Ala and Val f l a n k i n g T h ~-( ~' p ) , to give a new phosphohexapeptide reproducing the phosphorylated site of protein phosphatase inhibitor-1, prevents the protein phosphatase-T activity.Moreover, IgG heavy chain 32P labeled in tyrosine is not affected by protein phosphatase-T, while it is dephosphorylated by alkaline phosphatase.These results would indicate that protein phosphatase(s)-T represent a distinct class of protein phosphatases specifically involved in the dephosphorylation of phosphothreonyl residues fulfilling definite structural requirements. ~~Recently, it has been shown that some protein phosphatases distinct from the broad specificity protein phosphatase-1 (1) catalyze a preferential dephosphorylation of substrates containing phosphothreonyl (2) and phosphotyrosyl residues (3, 4) instead of the much more frequent and widespread phosphoseryl residues.However, the actual requirement of such phosphatases for a definite phosphoamino acid residue is not proven until their activity is tested on substrates differing not only in the nature of the phosphorylated residues but also in