Dataset Information

Aqueous access pathways in subunit a of rotary ATP synthase extend to both sides of the membrane.

ABSTRACT: The role of subunit a in promoting proton translocation and rotary motion in the Escherichia coli F1Fo ATP synthase is poorly understood. In the membrane-bound Fo sector of the enzyme, H+ binding and release occur at Asp-61 in the middle of the second transmembrane helix (TMH) of subunit c. Protons are thought to reach Asp-61 at the center of the membrane via aqueous channels formed at least in part by one or more of the five TMHs of subunit a. Aqueous access pathways have previously been mapped to surfaces of aTMH4. Here we have substituted Cys into the second and fifth TMHs of subunit a and carried out chemical modification with Ag+ and N-ethylmaleimide to define the aqueous accessibility of residues along these helices. Access to cAsp-61 at the center of the membrane may be mediated in part by Ag+-sensitive residues 248, 249, 251, and 252 in aTMH5. From the periplasmic surface, aqueous access to cAsp-61 may be mediated by silver-sensitive residues 115, 116, 119, 120, 122, and 126 in aTMH2. The Ag+-sensitive residues in TMH2, -4, and -5 form a continuum extending from the periplasmic to the cytoplasmic side of the membrane. In an arrangement of helices supported by second-site revertant and crosslinking analyses, these residues cluster at the interior of a four-helix bundle formed by TMH2-5. The aqueous access pathways at the interior of subunit a may be gated by a swiveling of helices in this bundle, alternately exposing cytoplasmic and periplasmic half channels to cAsp-61 during the H+ transport cycle.

SUBMITTER: Angevine CM

PROVIDER: S-EPMC263739 | biostudies-literature | 2003 Nov

REPOSITORIES: biostudies-literature

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Aqueous access pathways in subunit a of rotary ATP synthase extend to both sides of the membrane.

Angevine Christine M CM Herold Kelly A G KA Fillingame Robert H RH

Proceedings of the National Academy of Sciences of the United States of America 20031031 23

The role of subunit a in promoting proton translocation and rotary motion in the Escherichia coli F1Fo ATP synthase is poorly understood. In the membrane-bound Fo sector of the enzyme, H+ binding and release occur at Asp-61 in the middle of the second transmembrane helix (TMH) of subunit c. Protons are thought to reach Asp-61 at the center of the membrane via aqueous channels formed at least in part by one or more of the five TMHs of subunit a. Aqueous access pathways have previously been mapped ...[more]

PMID: 14595019

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Project description:The F(1)F(0)-adenosine triphosphate (ATP) synthase rotational motor synthesizes most of the ATP required for living from adenosine diphosphate, Pi, and a proton electrochemical gradient across energy-transducing membranes of bacteria, chloroplasts, and mitochondria. However, as a reversible nanomotor, it also hydrolyzes ATP during de-energized conditions in all energy-transducing systems. Thus, different subunits and mechanisms have emerged in nature to control the intrinsic rotation of the enzyme to favor the ATP synthase activity over its opposite and commonly wasteful ATPase turnover. Recent advances in the structural analysis of the bacterial and mitochondrial ATP synthases are summarized to review the distribution and mechanism of the subunits that are part of the central rotor and regulate its gyration. In eubacteria, the epsilon subunit works as a ratchet to favor the rotation of the central stalk in the ATP synthase direction by extending and contracting two alpha-helixes of its C-terminal side and also by binding ATP with low affinity in thermophilic bacteria. On the other hand, in bovine heart mitochondria, the so-called inhibitor protein (IF(1)) interferes with the intrinsic rotational mechanism of the central gamma subunit and with the opening and closing of the catalytic beta-subunits to inhibit its ATPase activity. Besides its inhibitory role, the IF(1) protein also promotes the dimerization of the bovine and rat mitochondrial enzymes, albeit it is not essential for dimerization of the yeast F(1)F(0) mitochondrial complex. High-resolution electron microscopy of the dimeric enzyme in its bovine and yeast forms shows a conical shape that is compatible with the role of the ATP synthase dimer in the formation of tubular the cristae membrane of mitochondria after further oligomerization. Dimerization of the mitochondrial ATP synthase diminishes the rotational drag of the central rotor that would decrease the coupling efficiency between rotation of the central stalk and ATP synthesis taking place at the F(1) portion. In addition, F(1)F(0) dimerization and its further oligomerization also increase the stability of the enzyme to natural or experimentally induced destabilizing conditions.

Dataset Information

Aqueous access pathways in subunit a of rotary ATP synthase extend to both sides of the membrane.

Publications

Aqueous access pathways in subunit a of rotary ATP synthase extend to both sides of the membrane.

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