Girvin M E, Rastogi V K, Abildgaard F, Markley J L, Fillingame R H
Department of Biomolecular Chemistry, University of Wisconsin Medical School, Madison 53706, USA.
Biochemistry. 1998 Jun 23;37(25):8817-24. doi: 10.1021/bi980511m.
Subunit c is the H+-translocating component of the F1F0 ATP synthase complex. H+ transport is coupled to conformational changes that ultimately lead to ATP synthesis by the enzyme. The properties of the monomeric subunit in a single-phase solution of chloroform-methanol-water (4:4:1) have been shown to mimic those of the protein in the native complex. Triple resonance NMR experiments were used to determine the complete structure of monomeric subunit c in this solvent mixture. The structure of the protein was defined by >2000 interproton distances, 64 (3)JN alpha, and 43 hydrogen-bonding NMR-derived restraints. The root mean squared deviation for the backbone atoms of the two transmembrane helices was 0.63 A. The protein folds as a hairpin of two antiparallel helical segments, connected by a short structured loop. The conserved Arg41-Gln42-Pro43 form the top of this loop. The essential H+-transporting Asp61 residue is located at a slight break in the middle of the C-terminal helix, just prior to Pro64. The C-terminal helix changes direction by 30 +/- 5 degrees at the conserved Pro64. In its protonated form, the Asp61 lies in a cavity created by the absence of side chains at Gly23 and Gly27 in the N-terminal helix. The shape and charge distribution of the molecular surface of the monomeric protein suggest a packing arrangement for the oligomeric protein in the F0 complex, with the front face of one monomer packing favorably against the back face of a second monomer. The packing suggests that the proton (cation) binding site lies between packed pairs of adjacent subunit c.
亚基c是F1F0 ATP合酶复合体的H⁺转运组分。H⁺转运与构象变化相偶联，最终导致该酶合成ATP。已证明在氯仿 - 甲醇 - 水（4:4:1）单相溶液中单体亚基的性质模拟了天然复合体中蛋白质的性质。利用三共振核磁共振实验确定了该溶剂混合物中单体亚基c的完整结构。蛋白质的结构由2000多个质子间距离、64个（3）J Nα以及43个基于核磁共振衍生的氢键限制所定义。两个跨膜螺旋主链原子的均方根偏差为0.63 Å。该蛋白质折叠成由两个反平行螺旋段组成的发夹结构，由一个短的结构化环连接。保守的Arg41 - Gln42 - Pro43形成该环的顶部。关键的H⁺转运Asp61残基位于C端螺旋中部稍靠后的位置，就在Pro64之前。C端螺旋在保守的Pro64处改变方向30±5度。在其质子化形式下，Asp61位于由N端螺旋中Gly23和Gly27处缺少侧链所形成的腔内。单体蛋白质分子表面的形状和电荷分布表明了F0复合体中寡聚蛋白质的堆积排列方式，一个单体的正面与第二个单体的背面有利地堆积在一起。这种堆积表明质子（阳离子）结合位点位于相邻亚基c的堆积对之间。
