Adenosine triphosphate-dependent degradation of a fluorescent lambda N substrate mimic by Lon protease

Escherichia coli Lon exhibits a varying degree of energy requirement toward hydrolysis of different substrates. Efficient degradation of protein substrates requires the binding and hydrolysis of ATP such that the intrinsic ATPase of Lon is enhanced during protein degradation. Degradation of synthetic tetrapeptides, by contrast, is achieved solely by ATP binding with concomitant inhibition of the ATPase activity. In this study, a synthetic peptide (FRETN 89-98), containing residues 89-98 of lambda N protein and a fluorescence donor (anthranilamide) and quencher (3-nitrotyrosine), has been examined for ATP-dependent degradation by E. coli and human Lon proteases. The cleavage profile of FRETN 89-98 by E. coli Lon resembles that of lambda N degradation. Both the peptide and protein substrates are specifically cleaved between Cys93 and Ser94 with concomitant stimulation of Lon's ATPase activity. Furthermore, the degradation of FRETN 89-98 is supported by ATP and AMPPNP but not ATPgammaS nor AMPPCP. FRETN 89-98 hydrolysis is eight times more efficient in the presence of 0.5 mM ATP compared to 0.5 mM AMPPNP at 86 microM peptide. The ATP-dependent hydrolysis of FRETN 89-98 displays sigmodial kinetics. The k(cat), [S](0.5), and the Hill coefficient of FRETN 89-98 degradation are 3.2 +/- 0.3 s(-1), 106 +/- 21 microM, and 1.6 respectively.