FEATURED MACHINE 09 / 12

Nuo respiratory complex I

Links electron transfer with membrane energy conversion.

LIBRARY BASIS · BACTERIAL ACCOUNT

The question behind this machine

The library emphasizes the connection between a chain of redox centres and a distant membrane pump. Its locomotive comparison is a visualization aid. The bacterial structure provides a firmer basis for discussing the actual protein modules and the coupling problem.^L1

From electron entry to a membrane response

The Thermus thermophilus structure joins a hydrophilic electron-transfer arm to a membrane arm. NADH-derived electrons pass through cofactor-containing modules toward quinone chemistry. The arrangement connects a local redox reaction with processes distributed along the membrane domain. A structural model reveals plausible coupling paths; it is not a direct movie of every proton-transfer event.^P1

Assembly and cofactor supply

The functional particle requires compatible subunits, membrane insertion and correctly placed redox cofactors. Listing a protein sequence inventory does not show that all cofactors have been inserted or that the assembled particle pumps ions. Assembly, electron transfer and energy conservation therefore need separate measurements.^P1

Precision across more than one scale

Electron carriers must occupy useful relative positions, while the membrane arm must couple chemical changes to ion movement. This combines short-range chemical recognition with communication across the larger complex. The relevant origin target is coordinated coupling, not merely an L-shaped aggregate. A resolution value should not be advertised as a biological manufacturing tolerance.^P1

Maintenance and explanatory limits

The library’s dependency question is valuable, but a familiar engineered shape does not establish a historical mechanism. Compare related redox and antiporter-like modules, alternative respiratory pathways and experimentally functional partial systems. Cofactor loss or membrane damage can impair activity without requiring the entire protein complex to have lost its fold.^P1

Connected to the rest of the cell

This machine depends on resources and supporting systems, and its work supplies other cellular processes.

FUNCTIONAL ORGANIZATION · AUTHOR’S FRAMEWORK

Hallmarks of design

Respiratory complex I illustrates the following organizational features in the supplied papers. These descriptions identify biological functions; interpreting their origin as design is the author’s comparative argument.^{H1, H2}

H15Molecular machines

Electron-transfer and membrane modules perform coupled work.

H22Gradient-based energy storage

Energy-conserving activity contributes to a membrane gradient.

H25Cofactor dependency networks

Electron carriers and metal centres require supply and maturation.

Origin hurdles and abductive assessment · Assessment method · All 40 hallmarks. Biological evidence: the mechanism, accession records and scientific references on this page.

Origins and explanatory assessment

INFERENCE TO THE BEST EXPLANATION · PROVISIONAL ASSESSMENT

From origin hurdles to a cautious inference

What needs explaining. Explain the historical coupling of redox carriers to ion-translocating membrane modules; homology and simpler related modules are relevant evidence.

Positive observations. Electron-transfer and membrane modules perform coupled work. Energy-conserving activity contributes to a membrane gradient.

Compare the explanations. The design proposal appeals to coordinated functional organization, not complexity alone. A natural account can include chemical affinities, self-assembly, co-option, duplication, common ancestry and selection where heredity exists; it need not draw a complete modern system in one random trial. Present operation, historical emergence and first-cell origins are separate questions.

Abductive conclusion. The coordinated features give the author a positive reason to consider design within the wider cellular architecture. For this local system alone, they do not establish that design is uniquely the best historical explanation. The conservative inference is that the system contributes to a cumulative design case, with its weight conditional on the comparative evidence and on how much plausible natural pathways explain.

What could change the assessment. Functional intermediates, sequence-family relationships and experimentally connected steps would strengthen a natural account in proportion to what they explain. Loss of a claimed dependency or discovery of functional alternatives would weaken the corresponding design argument. Gaps in the record do not supply a numerical likelihood for either explanation.

Method, assumptions and revision criteria^{H1, H2}. Evaluate alongside the origin discussion and scientific sources on this page.

Represented in the 912-protein inventory

13 selected protein entries. These entries identify selected components represented in the working inventory; they do not establish the complete composition or copy numbers of an assembled machine.

Gene / locus	Protein entry	Source record
nuoA2aq_1310	NADH-quinone oxidoreductase subunit A (EC 7.1.1.-) (NADH dehydrogenase I subunit A) (NDH-1 subunit A) (NUO1)	O67333 ↗
nuoBaq_1312	NADH-quinone oxidoreductase subunit B (EC 7.1.1.-) (NADH dehydrogenase I subunit B) (NDH-1 subunit B)	O67334 ↗
nuoC2aq_1314	NADH-quinone oxidoreductase subunit C/D 2 (EC 7.1.1.-) (NADH dehydrogenase I subunit C/D 2) (NDH-1 subunit C/D 2)	O67335 ↗
nuoHaq_1315	NADH-quinone oxidoreductase subunit H (EC 7.1.1.-) (NADH dehydrogenase I subunit H) (NDH-1 subunit H)	O67336 ↗
nuoIaq_1317	NADH-quinone oxidoreductase subunit I (EC 7.1.1.-) (NADH dehydrogenase I subunit I) (NDH-1 subunit I)	O67337 ↗
nuoJ1aq_1318	NADH-quinone oxidoreductase subunit J (EC 7.1.1.-)	O67338 ↗
nuoK1aq_1319	NADH-quinone oxidoreductase subunit K 1 (EC 7.1.1.-) (NADH dehydrogenase I subunit K 1) (NDH-1 subunit K 1)	O67339 ↗
nuoL1aq_1320	NADH dehydrogenase I chain L	O67340 ↗
nuoM1aq_1321	NADH dehydrogenase I chain M	O67341 ↗
nuoN1aq_1322	NADH-quinone oxidoreductase subunit N 1 (EC 7.1.1.-) (NADH dehydrogenase I subunit N 1) (NDH-1 subunit N 1)	O67342 ↗
nuoGaq_437	NADH dehydrogenase I chain G	O66748 ↗
nuoFaq_573	NADH-quinone oxidoreductase subunit F (EC 7.1.1.-) (NADH dehydrogenase I subunit F) (NDH-1 subunit F)	O66841 ↗
nuoEaq_574	NADH-quinone oxidoreductase subunit E (EC 7.1.1.-) (NADH dehydrogenase I subunit E) (NDH-1 subunit E)	O66842 ↗

Follow the evidence

Each source-record link opens its UniProt entry. Gene links open the corresponding entry in this atlas’s working inventory.

Related scientific references ↗

Sources for the developed article

Library essays and topic discussions

L1. Otangelo Grasso, Your Inner Locomotive Revealed. Machine or family-level discussion.

Primary scientific evidence

P1. Baradaran et al. (2013), Crystal structure of the entire respiratory complex I.

Numbered protein records establish the selected inventory entries; these experimental examples establish the mechanisms identified above. Results from another bacterial species are not automatically Aquifex-specific measurements. Explore the library-to-atlas source guide →