Expression of latent functions of heme proteins triggered by synthetic bilayr membranes

血红素蛋白独特功能的表达是由血红素-载脂蛋白相互作用决定的。如果这种相互作用通过蛋白质的三级结构进行修饰，一种新的功能控制方法就变得可行。存在于细胞色素c （Cyt-c）表面的赖氨酸残基在维持三级结构中起着重要作用。当其大部分氨基被马来酰化时，Cyt-c的球形结构转化为部分展开的结构。有趣的是，通过增加介质中的盐浓度，新结构恢复到原来的球形。这种转化伴随着血红素的轴向配位从HO-Fe-His18逐渐转变为Met80-Fe-His18。在功能方面，虽然天然的Cyt-c作为电子转移蛋白，但马来酰化蛋白在部分展开的结构中表现出过氧化物酶样的活性。在培养基中加入盐使蛋白质结构再转化后，过氧化物酶活性被抑制，电子传递功能增强。因此，表面赖氨酸残基的修饰导致三级结构和酶功能的改变。该方法同样适用于肌红蛋白，显示了其在酶工程中的丰富可能性。它揭示了一个与传统的一级结构改变的酶修饰完全不同的新方面，可能与催化熔融球的概念有关，熔融球显然参与了分子进化过程。

The expression of unique functions of heme proteins is determined by the heme-apoprotein interaction. A new methodology of the functional control become feasible if this interaction is modified via the tertiary structure of proteins. The lysine residues present on the surface of cytochrome c (Cyt-c) play an important role in the maintenance of the tertiary structure. When most of the its amino group is maleylated, the globular structure of Cyt-c is converted to a partially unfolded structure. Interestedly, the new structure returns to the original globular form by increasing the salt concentration of the medium. This conversion is accompanied by the gradual change of the axial coordination of the heme from HO-Fe-His18 to Met80-Fe-His18. In the functional aspect, although the natural Cyt-c acts as electron transfer protein, the maleylated protein shows a peroxydase like activity in the partially unfolded structure. Upon reconversion of the protein structure by addition of salts in the medium, the peroxydase activity is suppressed and electron transfer function is strengthened. Thus, the modification of the surface lysine residue leads to the concomitant changes of the tertiary structure and the enzyme function. This methodology is also applicable to myoglobin, showing its rich possibility in enzyme engineering. It reveals a new aspect that is quite different from the conventional enzyme modification by the altered primary structure, and may be related to the concept of catalytic molten globules that are apparently involved in the process of molecular evolution.