Dax Chantal, Coinçon Mathieu, Sygusch Jurgen, Blonski Casimir
Groupe de Chimie Organique Biologique, LSPCMIB UMR CNRS 5068, Université Paul Sabatier, Bâtiment IIR1, 118 Route de Narbonne, 31062 Toulouse Cedex 4, France.
Biochemistry. 2005 Apr 12;44(14):5430-43. doi: 10.1021/bi0477992.
Interactions of phosphate derivatives of 2,6-dihydroxynaphthalene (NA-P(2)) and 1,6-dihydroxy-2-naphthaldehyde (HNA-P, phosphate at position 6) with fructose-1,6-bisphosphate aldolase from rabbit muscle were analyzed by enzyme kinetics, difference spectroscopy, site-directed mutagenesis, mass spectrometry, and molecular dynamics. Enzyme activity was competitively inhibited by NA-P(2), whereas HNA-P exhibited slow-binding inhibition with an overall inhibition constant of approximately 24 nM. HNA-P inactivation was very slowly reversed with t(1/2) approximately 10 days. Mass spectrometry and spectrophotometric absorption indicated that HNA-P inactivation occurs by Schiff base formation. Rates of enzyme inactivation and Schiff base formation by HNA-P were identical and corresponded to approximately 4 HNA-P molecules bound par aldolase tetramer at maximal inhibition. Site-directed mutagenesis of conserved active site lysine residues 107, 146, and 229 and Asp-33 indicated that Schiff base formation by HNA-P involved Lys-107 and was promoted by Lys-146. Titration of Lys-107 by pyridoxal 5-phosphate yielded a microscopic pK(a) approximately 8 for Lys-107, corroborating a role as nucleophile at pH 7.6. Site-directed mutagenesis of Ser-271, an active site residue that binds the C(1)-phosphate of dihydroxyacetone phosphate, diminished HNA-P binding and enabled modeling of HNA-P in the active site. Molecular dynamics showed persistent HNA-P phosphate interactions with the C(1)-phosphate binding site in the noncovalent adduct. The naphthaldehyde hydroxyl, ortho to the HNA-P aldehyde, was essential for promoting carbinolamine precursor formation by intramolecular catalysis. The simulations indicate a slow rate of enzyme inactivation due to competitive inhibition by the phenate form of HNA-P, infrequent nucleophilic attack in the phenol form, and significant conformational barrier to bond formation as well as electrostatic destabilization of protonated ketimine intermediates. Solvent accessibility by Lys-107 Nz was reduced in the covalent Schiff base complex, and in those instances where water molecules interacted with Lys-107 in the simulations, Schiff base hydrolysis was not mechanistically favorable. The findings at the molecular level corroborate the observed mechanism of slow-binding tight inhibition by HNA-P of muscle aldolase and should serve as a blueprint for future aldolase inhibitor design.
通过酶动力学、差示光谱法、定点诱变、质谱分析法和分子动力学方法,分析了2,6 - 二羟基萘的磷酸衍生物(NA - P(2))和1,6 - 二羟基 - 2 - 萘甲醛(HNA - P,6位磷酸化)与兔肌肉果糖 - 1,6 - 二磷酸醛缩酶的相互作用。NA - P(2)竞争性抑制酶活性,而HNA - P表现出缓慢结合抑制作用,总体抑制常数约为24 nM。HNA - P导致的失活作用恢复非常缓慢,半衰期约为10天。质谱分析和分光光度吸收表明,HNA - P导致的失活是通过席夫碱形成实现的。HNA - P导致的酶失活速率和席夫碱形成速率相同,在最大抑制时,每分子醛缩酶四聚体约结合4个HNA - P分子。对保守的活性位点赖氨酸残基107、146和229以及天冬氨酸 - 33进行定点诱变表明,HNA - P形成席夫碱涉及赖氨酸 - 107,并受到赖氨酸 - 146的促进。用磷酸吡哆醛滴定赖氨酸 - 107得到赖氨酸 - 107的微观pK(a)约为8,证实了其在pH 7.6时作为亲核试剂的作用。对结合磷酸二羟丙酮C(1) - 磷酸的活性位点残基丝氨酸 - 271进行定点诱变,减少了HNA - P的结合,并使得能够对活性位点中的HNA - P进行建模。分子动力学显示,在非共价加合物中,HNA - P的磷酸基团与C(1) - 磷酸结合位点持续相互作用。HNA - P醛基邻位的萘甲醛羟基对于通过分子内催化促进甲醇胺前体形成至关重要。模拟结果表明,由于HNA - P酚盐形式的竞争性抑制、酚形式中亲核攻击频率低、键形成存在显著构象障碍以及质子化酮亚胺中间体的静电不稳定,导致酶失活速率缓慢。在共价席夫碱复合物中,赖氨酸 - 107 Nz的溶剂可及性降低,并且在模拟中水分子与赖氨酸 - 107相互作用的情况下,席夫碱水解在机制上并不有利。分子水平的研究结果证实了观察到的HNA - P对肌肉醛缩酶的缓慢结合紧密抑制机制,应为未来醛缩酶抑制剂的设计提供蓝图。