QUANTITATIVE-ANALYSIS OF THE EFFECT OF ACANTHAMOEBA PROFILIN ON ACTIN FILAMENT NUCLEATION AND ELONGATION
QUANTITATIVE-ANALYSIS OF THE EFFECT OF ACANTHAMOEBA PROFILIN ON ACTIN FILAMENT NUCLEATION AND ELONGATION
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DOI：
10.1021/bi00321a054
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发表时间：
1984-01-01
期刊：
影响因子：
2.9
通讯作者：
COOPER, JA
中科院分区：
文献类型：
--
作者：
POLLARD, TD;COOPER, JA
目前对阿米巴profilin作用机制的看法是，它与肌动蛋白单体结合，形成一种不能降解的复合物。这个简单的模型不能预测在50 mM KCl、1 mM MgCl 2和1 mM EGTA [乙二醇双（β-葡糖苷酸）]中用阿米巴肌动蛋白进行的2个新的实验观察结果。氨基乙基醚）-N，N，N“，N”-四乙酸]。首先，阿米巴profilin抑制肌动蛋白丝的伸长远超过在尖端比在倒刺结束。根据该简单模型，基于在尖端的观察结果，前纤维蛋白-肌动蛋白复合物的Kd小于5 μ M，而倒刺末端的Kd大于50 μ M。第二，profilin抑制成核比延伸更强烈。根据该简单模型，基于2种延伸测定，前纤维蛋白-肌动蛋白复合物的Kd为60-140 μ M，但基于反映成核的聚合动力学，Kd为2-10 μ M。这些新发现可以用一个新的、更复杂的作用机制模型来解释，该模型与Tilney及其同事的提议有关。在该模型中，前纤维蛋白可以以约5 μ M的Kd与肌动蛋白单体结合，并以约50-100 μ M的Kd与肌动蛋白丝的倒刺末端结合。与profilin结合的肌动蛋白单体不能参与成核或添加到肌动蛋白丝的尖端。它可以添加到细丝的倒刺末端。当profilin被绑定到一个长丝的倒刺端，肌动蛋白单体不能结合到该结束，但终端肌动蛋白原聚体可以解离在通常的速度。该模型包括2个不同的Kd：一个用于与肌动蛋白单体结合的profilin，一个用于与细丝的倒刺末端处的肌动蛋白分子结合的profilin。对细丝末端的亲和力比对单体的亲和力低10倍，可能是由于2种形式肌动蛋白的构象差异或细丝末端的空间限制。
The current view of the mechanism of action of Acanthamoeba profilin is that it binds to actin monomers, forming a complex that cannot polymerize. This simple model fails to predict 2 new experimental observations made with Acanthamoeba actin in 50 mM KCl, 1 mM MgCl2 and 1 mM EGTA [ethylene glycol bis(.beta.-aminoethyl ether)-N,N,N'',N''-tetraacetic acid]. First, Acanthamoeba profilin inhibits elongation of actin filaments far more at the pointed end than at the barbed end. According to the simple model, the Kd for the profilin-actin complex is less than 5 .mu.M on the basis of observations at the pointed end and greater than 50 .mu.M for the barbed end. Second, profilin inhibits nucleation more strongly than elongation. According to the simple model, the Kd for the profilin-actin complex is 60-140 .mu.M on the basis of 2 assays of elongation but 2-10 .mu.M on the basis of polymerization kinetics that reflect nucleation. These new findings can be explained by a new and more complex model for the mechanism of action that is related to a proposal of Tilney and co-workers. In this model, profilin can bind both to actin monomers with a Kd of about 5 .mu.M and to the barbed end of actin filaments with a Kd of about 50-100 .mu.M. An actin monomer bound to profilin cannot participate in nucleation or add to the pointed end of an actin filament. It can add to the barbed end of a filament. When profilin is bound to the barbed end of a filament, actin monomers cannot bind to that end, but the terminal actin protomer can dissociate at the usual rate. This model includes 2 different Kd: one for profilin bound to actin monomers and one for profilin bound to an actin molecule at the barbed end of a filament. The affinity for the end of the filament is lower by a factor of 10 than the affinity for the monomer, presumably due to the difference in the conformation of the 2 forms of actin or to steric constraints at the end of the filament.