DETERMINANTS OF RECEPTOR SPECIFICITY OF COLIPHAGES OF THE T4 FAMILY - A CHAPERONE ALTERS THE HOST-RANGE
DETERMINANTS OF RECEPTOR SPECIFICITY OF COLIPHAGES OF THE T4 FAMILY - A CHAPERONE ALTERS THE HOST-RANGE
复制标题
DOI：
10.1006/jmbi.1994.1529
复制
发表时间：
1994-08-26
影响因子：
5.6
通讯作者：
HENNING, U
中科院分区：
文献类型：
--
作者：
HASHEMOLHOSSEINI, S;MONTAG, D;HENNING, U
大肠杆菌T4家族噬菌体（T4, TuIa, TuIb）通过蛋白37的c端区域识别其细胞受体。这种蛋白是所有三种噬菌体共有的，以二聚体的形式存在于长尾纤维的远端，具有由40至70个高度保守的c端残基组成的c端结构域，然后是50至80个残基的可变区域，然后是高度保守的区域。蛋白质38不是成熟病毒粒子的组成部分，是蛋白质37二聚化所必需的；这代表了结构蛋白的非共价结合。分析了7个TuIa或TuIb的宿主范围突变体，这些突变体能够使用与其亲本不同的蛋白质受体。所有的变异区都发生了氨基酸替换。结论是，很可能是这个区域直接与细胞受体相互作用。已知T4的条件突变体，当在非允许温度（42℃）下繁殖时，产生正常形态的噬菌体，但这些噬菌体或多或少不能吸附到细胞上。在可变区域的上游和下游都发现了致病氨基酸取代。它在突变体中的扭曲可能表明尾部纤维的“快速恢复”构象；所述保守的c端区域可向后折叠并将所述可变区域暴露为光纤尖端的环路。其中一种噬菌体突变体（L93）在允许的温度下生长时，失去了使用OmpC孔蛋白（T4的受体）作为受体的能力。一个二级突变体，能够做到这一点，被分离出来。在38号基因上发生了一个额外的突变，导致一个氨基酸的替换。该突变基因以反式方式起作用，导致传染性的温度敏感性大大增强，而不赋予温度敏感性本身，即突变蛋白38明显改变了蛋白37二聚体的受体识别区域的构象。来自噬菌体lambda的基因与T4的38号基因大约40%相同，与38号基因琥珀突变体互补。相应的蛋白也恢复了L93对OmpC的识别能力，但没有引起这种温度敏感性。因此，归类为伴侣的蛋白38似乎在向靶多肽传递立体信息方面起指导作用。
E. coli phages of the T4 family (T4, TuIa, TuIb) recognize their cellular receptors with a C-terminal region of protein 37. This protein, common to all three phages, is present as a dimer located at the distal part of the long tail fibers and possesses a C-terminal domain consisting of 40 to 70 highly conserved C-terminal residues, followed by a variable region of 50 to 80 residues which is again followed by a highly conserved area. Protein 38, not being a component of the mature virion, is required for dimerization of protein 37; this represents a non-covalent association of a structural protein. Seven host range mutants of TuIa or TuIb were analyzed which were able to use proteinaceous receptors other than those recognized by their parents. All had suffered amino acid substitutions within the variable region. It is concluded that in all probability it is this region which interacts directly with the cellular receptors. Conditional mutants of T4 are known which, when propagated at the non-permissive temperature (42 degrees C), yield phage of normal morphology but these are more or less unable to adsorb to cells. The causative amino acid substitutions were found both downstream and upstream from the variable area. Distortion of it in the mutants could suggest a ''snap-back'' conformation of the tail fiber; the conserved C-terminal region may fold back and expose the variable region as a loop at the tip of the fiber. One of the phage mutants (L93), when grown at the permissive temperature, had lost the ability to use the OmpC porin (a receptor for T4) as a receptor. A secondary mutant, able to do so, was isolated. An additional mutation, leading to one amino acid substitution, had occurred in gene 38. This mutant gene acted in trans and caused a much enhanced temperature-sensitivity of infectivity without conferring temperature-sensitivity per se, i.e. the mutant protein 38 apparently altered the conformation of the receptor-recognizing area of the dimer of protein 37. A gene from phage lambda, about 40% identical to gene 38 of T4, complements gene 38 amber mutants. The corresponding protein also restored the ability of L93 to recognize OmpC but did not cause any such temperature-sensitivity. Hence, protein 38, classifying as a chaperone, appears to act instructively in conveying steric information to the target polypeptide.