POLYPEPTIDE STRUCTURE AND DYNAMICS CONTROLLED BY PHOT0-ISOMERIZATION

In order to clarify the mechanism of the helix-sense inversion of poly（β-n-propyl）l-aspartate) (pnpla),the conformational transition of PnPLA and its derivative with azobenzene group were investigated bymeans of NMR.1) The right-handed α-helix (α - D2R - D2)of PnPLA can change thermoreversibly to Theleft-handed (α - D2L - D2) with increasing temperature from 30 to 70℃in CDCl - D23 - D2. The midpointtransition free energy is 110 kJ/mol / 50℃and the exchange rate between both conformations is 5 /s at about 50℃。All the D113 D1C signalsPnPLA can separate completely between the right- and left-helicesalthough only the NH and β D2s D2 proton resonances show the conformational dependence. Theseresults indicate that the side-chain conformation of α D2R D2-helical PnPLA is different from thatof α - D2L -helix，as well as the main chain conformation. the α - d -helix conformation of PnPLA changes to the(left - handed,并subsequently to the random-coil with increasing the trifluoroacetic acid concentration. the coilconformation of PnPLA can change to the α D2L -helix with increasing the temperature，D2R D2-helix is not detected in the high temperatures.2) PnPLA containing 30%p-phenylazobenzene group in the side chain do not show the helix-sense inversion with thephoto-isomerization of azobenzene group. The PnPLA containing more than 50% p-phenylazobenzene group3) The internal rotational angle from The spin-spin couplingD1Jαβ是必要的determine the side chain conformation. the monomer ofL-asp-β D2R D2-d was successfully synthesized from the fumaric acid in D22 D2O/ND D24 D2ODwith the enzyme of L-aspartase to remove the contribution of the residual geminal d - 1j ββ inthe signal of β - D2s - D2 proton. PnPLA-β - D2R -d -d is preparing for further实验。

In order to clarify the mechanism of the helix-sense inversion of poly(β-n-propyl L-aspartate)(PnPLA), the conformational transition of PnPLA and its derivative with azobenzene group were investigated by means of NMR.1) The right-handed α-helix (αィイD2RィエD2)of PnPLA can change thermoreversibly to the left-handed (αィイD2LィエD2) with increasing temperature from 30 to 70℃ in CDClィイD23ィエD2. The midpoint is 50℃, the transition free energy is 110 kJ/mol, and the exchange rate between both conformations is 5 /s at about 50℃. All the ィイD113ィエD1C signals of PnPLA can separate completely between the right- and left-helices, although only the NH and βィイD2sィエD2 proton resonances show the conformational dependence. These results indicate that the side-chain conformation of αィイD2RィエD2-helical PnPLA is different from that of αィイD2LィエD2-helix, as well as the main chain conformation. The αィイD2RィエD2-helix conformation of PnPLA changes to the left-handed, and subsequently to the random-coil with increasing the trifluoroacetic acid concentration. The coil conformation of PnPLA can change to the αィイD2LィエD2-helix with increasing the temperature, and the αィイD2RィエD2-helix is not detected in the high temperatures.2) PnPLA containing 30% p-phenylazobenzene group in the side chain do not show the helix-sense inversion with the photo-isomerization of azobenzene group. The PnPLA containing more than 50% p-phenylazobenzene group is preparing for further experiments.3) The internal rotational angle from the spin-spin coupling constant ィイD13ィエD1Jαβ is necessary to determine the side chain conformation. The monomer of L-asp-βィイD2RィエD2-d was successfully synthesized from the fumaric acid in DィイD22ィエD2O/NDィイD24ィエD2OD with the enzyme of L-aspartase to remove the contribution of the residual geminal ィイD12ィエD1Jββ in the signal of βィイD2sィエD2 proton. PnPLA-βィイD2RィエD2-d is preparing for further experiments.