Ahmad S, Glavas N A, Bragg P D
Department of Biochemistry, University of British Columbia, Vancouver, Canada.
J Mol Biol. 1993 Nov 5;234(1):8-13. doi: 10.1006/jmbi.1993.1559.
The pyridine nucleotide transhydrogenase of Escherichia coli is an inner membrane protein of two different subunits (alpha and beta). It functions as a proton pump. The highly hydrophilic carboxy-terminal tail of ten amino acid residues in the alpha-subunit determines the correct folding and proper assembly of the beta-subunit leading to a functional enzyme. Premature termination of the alpha-subunit six amino acid residues from the carboxy-terminal end abolishes the activity completely. Although the two subunits are still assembled into the membrane, the conformation of the beta-subunit is perturbed. Systematic truncation and site-directed substitutions revealed that at least one positive charge in the carboxy-terminal region is required for efficient assembly of the two subunits to give a functional enzyme, while a phenylalanine residue, essential for activity, has no apparent effect on the extent of assembly of the two subunits.
大肠杆菌的吡啶核苷酸转氢酶是一种由两个不同亚基（α和β）组成的内膜蛋白。它起着质子泵的作用。α亚基中具有十个氨基酸残基的高度亲水的羧基末端尾巴决定了β亚基的正确折叠和正确组装，从而形成有功能的酶。α亚基从羧基末端起六个氨基酸残基处的提前终止会完全消除活性。尽管两个亚基仍组装到膜中，但β亚基的构象受到干扰。系统的截短和定点取代表明，羧基末端区域中至少一个正电荷是两个亚基有效组装以形成有功能酶所必需的，而对于活性至关重要的苯丙氨酸残基对两个亚基的组装程度没有明显影响。
