Low-affinity platelet factor 4 1H NMR derived aggregate equilibria indicate a physiologic preference for monomers over dimers and tetramers.
Low-affinity platelet factor 4 1H NMR derived aggregate equilibria indicate a physiologic preference for monomers over dimers and tetramers.
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低亲和力血小板因子 4 1H NMR 得出的聚集体平衡表明单体相对于二聚体和四聚体的生理偏好。
DOI：
10.1021/bi00218a007
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发表时间：
1991
期刊：
影响因子：
2.9
通讯作者：
Mayo,KH
中科院分区：
文献类型：
--
作者：
Mayo,KH
5月21日，……九百九十;低亲和力血小板因子4（LA-PF 4）与另一种相关的、顺序同源（约50%）的血小板特异性蛋白血小板因子4（PF 4）不同，是一种活性促有丝分裂和趋化剂。PF 4对肝素表现出高的结合亲和力，而LA-PF 4则没有。PF 4和LA-PF 4都可以以二聚体和四聚体聚集态存在。最近已经从源自质子核磁共振（NMR）积分的分数群体估计了PF 4聚集的平衡常数，所述积分被分配给单体、二聚体和四聚体状态中的共振[马约和陈（Chen）（1989）生物化学28，9469]，在500-MHz NMR时间尺度上，LA-PF 4聚集体之间相对缓慢的交换也使得Tyr 15环质子共振被分配为LA-PF 4中的单体、二聚体和四聚体状态。作为pH和离子强度的函数，LA-PF 4二聚体（KD）和四聚体（KT）形成的平衡缔合常数已从Tyr 15环质子共振积分估计。在低离子强度下，KD在pH 3下达到最小值12 M-1，其中KT处于其最大值1.6 X 105 M-1。在pH 4.1时，KD和KT具有相同的值，1.1 × 103 M-1，这是的最小值。在pH 5.5下稳定至其最大值2.2 X 104 M-1。这些值显著低于PF 4的值。KD和KT的pH依赖性分析表明，在单体-单体结合过程中，Glu/Asp和Lys/Arg侧链之间的静电相互作用可能形成主导力，即KD，而由于近端亚基间Glu/Asp残基引起的类似电荷排斥随着pH的升高而降低。在pH 7和低离子强度下，二聚体状态比四聚体状态更有利。在pH 7下升高溶剂离子强度使二聚体状态不稳定。在这些更生理的条件下，即pH 7和0.1-0.2 M NaCl，LA-PF 4单体比二聚体和四聚体更受青睐。对于在类似溶剂条件下的PF 4，四聚体占主导地位。这些同源血小板特异性蛋白之间的生物活性差异可能至少部分是不同聚集特性的结果。PF 4的生物活性状态为四聚体，而LA-PF 4的生物活性状态为单体。低亲和力血小板因子4（LA-PF 4）1属于一组免疫学上相同的血小板特异性蛋白质，与N-末端裂解产物相关，其他蛋白质包括β-血小板球蛋白（β-thromboglobulin，β TG）和血小板碱性蛋白（platelet basic protein，PBP）。LA-PF 4由85个氨基酸残基组成（Niewiarowski等人，1980; Holt & Niewiarowski，1980）。β TG和PBP的氨基酸序列与LA-PF 4的氨基酸序列完全相同
May 21,¡ 990; Revised Manuscript Received September 12, 1990 abstract: Low-affinity platelet factor 4 (LA-PF4), unlike another related, sequentially homologous (about 50%) platelet-specific protein, platelet factor 4 (PF4), is an active mitogenic and chemotactic agent. PF4 exhibits a high binding affinity for heparin, while LA-PF4 does not. Both PF4 and LA-PF4 can exist in dimer and tetramer aggregatestates. Equilibrium constants for PF4 aggregation have recently been estimated from fractional populations derived from proton nuclear magnetic resonance (NMR) integrals assigned to resonances in monomer, dimer, and tetramer states [Mayo & Chen (1989) Biochemistry 28, 9469], On a 500-MHz NMR time scale, relatively slow exchange among LA-PF4 aggregate specieshas also allowed Tyr 15 ring proton resonances to be assigned for monomer, dimer, and tetramer states in LA-PF4. As a function of pH and ionic strength, equilibrium association constants for LA-PF4 dimer (KD) and tetramer (KT) formation have been estimated from Tyr 15 ring proton resonance integrals. At low ionic strength, KD reaches a minimum value of 12 M" 1 at pH 3 where KT is at its maximum value of 1.6 X 105 M_1. At pH 4.1, KD and KT have the same value, 1.1 X 103 M-1, which is the minimum value for. plateaus off to its maximum value of 2.2 X 104 M" 1 by pH 5.5. These values are significantly lower than those for PF4. Analysis of the pH dependence of KD and KT suggests that electrostatic interactions probably among Glu/Asp and Lys/Arg side chains form the predominant force in the monomer-monomer binding process, ie, KD, while like-charge repulsiondue to proximal, intersubunit Glu/Asp residues decreases as the pH is raised. At pH 7 and low ionic strength, the dimer state is highly favored over the tetramer state. Elevating the solvent ionic strength at pH 7 destabilizes the dimer state. Under these more physiologic conditions, ie, pH 7 and 0.1-0.2 M NaCl, LA-PF4 monomers are highly favored over dimers and tetramers. For PF4 under similar solvent conditions, tetramers predominate. Differences in biological activities between these homologous platelet-specific proteins may be the result, at least in part, of differing aggregation properties. The biologically active state for PF4 is tetramer, while for LA-PF4 it is monomer. Quaternary structure may, therefore, account for strong heparin binding in PF4, most likely by presenting a more favorable structural matrix for effective glycosaminoglycan interactions.Ijow-affinity platelet factor 4 (LA-PF4) 1 belongs to a set of immunologically identical platelet-specific proteins related as N-terminal cleavage products; the others in this set are/3-thromboglobulin (/3TG) and platelet basic protein (PBP). LA-PF4 is composed of 85 amino acid residues (Niewiarowski et al., 1980; Holt & Niewiarowski, 1980). The amino acid sequences of/3TG andPBP are identical with that of LA-PF4