BINARY-LIQUID PHASE-SEPARATION OF LENS PROTEIN SOLUTIONS
BINARY-LIQUID PHASE-SEPARATION OF LENS PROTEIN SOLUTIONS
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DOI：
10.1073/pnas.88.13.5660
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发表时间：
1991-07-01
影响因子：
11.1
通讯作者：
BENEDEK, GB
中科院分区：
文献类型：
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作者：
BROIDE, ML;BERLAND, CR;BENEDEK, GB
我们测定了纯化的小牛晶状体蛋白水溶液的共存曲线(相分离温度T与蛋白浓度C的关系图)。所研究的蛋白质，小牛Gamma-IIa-、Gamma-IIIb-和Gamma-IVa-Crystal allin，具有非常相似的氨基酸序列和三维结构。测量共存曲线的上升段和下降段。我们发现，在临界点附近，这些蛋白质和晶状体蛋白的共存曲线可以用函数/(C(C)-C)/C(C)/=A[(T(C)-T)/T(C)]β来拟合，其中β=0.325，C(C)是蛋白质的临界浓度(mg/ml)，T(C)是相分离的临界温度(K)，A是表征共存曲线宽度的参数。我们发现，对于所有四条共存曲线(A=2.6+/-0.1，C(C)=289+/-20 mg/ml)，A和C(C)大致相同，但T(C)不同。对于Gamma-II和Gamma-IIib晶体蛋白，T(C)几乎等于5℃，而对于Gamma-IIIa和Gamma-IVa晶体蛋白，T(C)几乎等于38℃。通过比较已发表的小牛、大鼠和人γ-晶体蛋白的蛋白质序列，我们推测一些关键的氨基酸残基可以解释伽马-晶体蛋白分为低T(C)和高T(C)两个基团。
We have determined the coexistence curves (plots of phase-separation temperature T versus protein concentration C) for aqueous solutions of purified calf lens proteins. The proteins studied, calf gamma-IIIa-, gamma-IIIb-, and gamma-IVa-crystallin, have very similar amino acid sequences and three-dimensional structures. Both ascending and descending limbs of the coexistence curves were measured. We find that the coexistence curves for each of these proteins and for gamma-II-crystallin can be fit, near the critical point, to the function /(C(c) - C)/C(c)/= A[(T(c) - T)/T(c)]beta, where beta = 0.325, C(c) is the critical protein concentration in mg/ml, T(c) is the critical temperature for phase separation in K, and A is a parameter that characterizes the width of the coexistence curve. We find that A and C(c) are approximately the same for all four coexistence curves (A = 2.6 +/- 0.1, C(c) = 289 +/- 20 mg/ml), but that T(c) is not the same. For gamma-II- and gamma-IIIb-crystallin, T(c) almost-equal-to 5-degrees-C, whereas for gamma-IIIa- and gamma-IVa-crystallin, T(c) almost-equal-to 38-degrees-C. By comparing the published protein sequences for calf, rat, and human gamma-crystallins, we postulate that a few key amino acid residues account for the division of gamma-crystallins into low-T(c) and high-T(c) groups.