共 51 条
THE INTERACTION OF THE 2'-OH GROUP WITH THE VICINAL PHOSPHATE IN RIBONUCLEOSIDE 3'-ETHYLPHOSPHATE DRIVES THE SUGAR-PHOSPHATE BACKBONE INTO UNIQUE (S,EPSILON(-)) CONFORMATIONAL STATE
被引:30
作者:
PLAVEC, J
[1
]
THIBAUDEAU, C
[1
]
VISWANADHAM, G
[1
]
SUND, C
[1
]
SANDSTROM, A
[1
]
CHATTOPADHYAYA, J
[1
]
机构:
[1] UNIV UPPSALA, CTR BIOMED, DEPT BIOORGAN CHEM, S-75123 UPPSALA, SWEDEN
来源:
关键词:
D O I:
10.1016/0040-4020(95)00714-J
中图分类号:
O62 [有机化学];
学科分类号:
070303 ;
081704 ;
摘要:
The analysis of temperature-dependent vicinal proton-proton coupling constants has shown that the North (N) reversible arrow South (S) pseudorotational equilibria of ribonucleoside 3'-ethylphosphates [ApEt (21), GpEt (22), CpEt (23), rTpEt (24) and UpEt (25)], modelling simple diribonucleoside(3'-->5')monophosphate without any intramolecular base-base slacking, are driven more towards the South-type sugar (S) by Delta Delta H degrees approximate to -2.5 kJ mol(-1) in the case of purine and by approximate to -3.8 kJ mol(-1) in the case of pyrimidine nucleotides compared to the corresponding parent ribonucleosides 1 - 5. In contrast, the S-type sugar conformation in 2'-deaxyribonucleoside 3'-ethylphosphates (ref. 3d) is stabilized by Delta Delta H degrees approximate to -1.9 kJ mol(-1) in both purine and pyrimidine nucleotides compared to the parent 2'-deoxyribonucleosides. The total energetic effect of 2'-OH group due to its interaction with the vicinal phosphate in ribonucleotides in contrast with the corresponding 2'-deoxynucleotide counterparts can be assessed by subtracting the free-energies of N reversible arrow S pseudorotational equilibria in the ribonucleotide analogs 21 - 25 from the corresponding 2'-deoxynitcleotide counterparts 16 - 20 : Delta Delta G(298) approximate to +0.3 kJ mol(-1) in ApEt (21), +0.6 kJ mol(-1) in GpEt (22), +2.1 kJ mol(-1) CpEt (23), +1.1 kJ mol(-1) in rTpEt (24) and +1.3 kJ mol(-1) in UpEt (25). The additional stabilization of the S-type pseudorotamers in ribonucleoside 3'-ethylphosphates 21-25 compared to ribonucleoside 3'-monophosphates 11 - 15 by Delta Delta H degrees approximate to -2.0 kJ mol(-1) is attributed to the influence of the 2'-OH group in the former. The population of epsilon(t) rotamers increases by 7-13% from 278 to 358K, which corresponds also, with an equal increase of he population of N-type pseudorotamers, suggesting a unique cooperativity in the two-state (N,epsilon(t) reversible arrow (S,epsilon) conformational equilibria in 21 - 25. These cooperative conformational transitions of (N,epsilon(t)) reversible arrow (S,epsilon) equilibrium in 21 - 25 have been found to De orchestrated by the interaction of 2'-hydroxyl group with the vicinal phosphate as evident by the non-equivalent methylene protons of the 3'-ethylester function up to 348K in 21 - 25 compared to the 2'-deoxynucleotide counterparts 16 - 20 (ref. 3d). The intramolecular interaction of the 2'-OH function with the vicinal phosphodiester stabilizes the S and E. conformers (''On'' switch), whereas 2'-OH in a non-interacting state stabilizes the N and epsilon(t) conformers (''Off'' switch) in 21 - 25. The strengths of this ''On-Off'' molecular switch for the preference of(S,epsilon) conformational stale over (N,epsilon(t)) state in 21-25 are as follows: Delta G(298) approximate to -2.8 kJ mol(-1) for adenosine 3'-ethylphosphate (21), 2.1 kJ mol(-1) for guanosine 3'-ethylphosphate (22), approximate to 0.1 kJ mol(-1) for cytidine 3'-ethylphosphate (23), -0.9 kJ mol(-1) for ribothymidine 3'-ethylphosphate (24) and -0.7 kJ mol(-1) for uridine 3'-ethylphosphate (25).
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页码:11775 / 11792
页数:18
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