Carnitine/acylcarnitine translocase - 3D Mechanism Simulator

Loading structural data… (1OKC)

References & Databases

START HERE — how to read acylcarnitine(IMS) ⇌ acylcarnitine(matrix) A mitochondrial-carrier cartoon on the bovine ANT frame that actually exists: 1OKC (2.20 Å) + carboxyatractyloside. Human CACT (O43772, SLC25A20) has no PDB — fold analog / gene hedge. ANT ≠ CACT. CATR is a named inhibitor, not acylcarnitine and not carnitine. Palmitoylcarnitine and L-carnitine are [schematic]. This page is a carrier, not an EC enzyme. No ACT_SITE. Arg79 ★ is a deposited CATR-contact arginine on this ANT frame, not a catalytic base. Measured Å are deposited 1OKC pairs only. Schematic cargo Å are not geomClaims. Cardiolipin is not this cartoon. CPT2 is next.
Crystal structures PDB 1OKC — bovine ADP/ATP carrier (ANT1) + carboxyatractyloside, 2.20 Å (Pebay-Peyroula 2003). Coordinates are public. This is ANT (P02722, SLC25A4), not CACT. Human CACT UniProt O43772 has no PDB. CATR locks the c-state from the IMS. Cardiolipin in 1OKC is not extracted.
Mechanism — MCF antiport, not catalysis CACT (SLC25A20) exchanges acylcarnitine against free carnitine across the inner membrane. No EC number. Charged motif contacts are compiled from CACT mutagenesis (PMID:20347717) onto this ANT mesh. Arg79 ★ on screen is the 1OKC CATR contact, not a CACT ACT_SITE. ANT nucleotide transport is not shown. Source: UniProt O43772 · Pebay-Peyroula 2003 · Giangregorio 2010
0 — Setup: ANT cavity with CATR 1OKC holds CATR in the cavity. The inhibitor is shown so the lock can be named, then hidden when schematic cargo enters. Arg79 NH2 ⋯ CXT O23 = 2.61 Å. Asp231 OD1 ⋯ CXT O21 = 2.62 Å. Human CACT has no PDB; this mesh is ANT. Opaque, run:null (no autoplay).Source: PDB 1OKC (2.20 Å)
① — Palmitoylcarnitine binds from the IMS [schematic] Palmitoylcarnitine docks from the IMS onto the CATR seat. CATR is hidden: it is an inhibitor, not this cargo. Lys22 NZ ⋯ Arg79 NH2 = 3.42 Å is deposited 1OKC. Schematic cargo Å are not geomClaims.Source: schematic palmitoylcarnitine on 1OKC CATR seat
② — Carrier inverts, c-state to m-state (hypothetical, lit.-based) The MCF carrier inverts [schematic]. The protein mesh is static — 1OKC is the CATR-locked c-state. No catalytic residue. Slow-motion on purpose.Source: compiled MCF ping-pong · Giangregorio 2010 PMID:20347717
③ — Palmitoylcarnitine leaves to the matrix [schematic] Palmitoylcarnitine departs toward the matrix. Antiport cargo release, not a chemical reaction. CPT2 next will transfer the acyl chain back onto CoA.Source: β-oxidation bookkeeping · SLC25A20
④ — Free carnitine returns to the IMS — CPT2 next [schematic] L-carnitine enters from the matrix side, docks, then departs toward the IMS — compiled ping-pong return, not a second invert movie. Net: acylcarnitine(IMS) + carnitine(matrix) ⇌ acylcarnitine(matrix) + carnitine(IMS). Matrix palmitoylcarnitine (C16) is the substrate of CPT2. This page does not transesterify.Source: β-oxidation bookkeeping · SLC25A20

How to read this page — a first-pass primer First pass: Setup (ANT cavity, CATR inhibitor, Arg79 ★, fold analog) → ① schematic palmitoylcarnitine docks from the IMS → ② schematic invert, c → m → ③ palmitoylcarnitine leaves to the matrix → ④ free carnitine enters from the matrix and returns to the IMS; CPT2 next (C16 cargo). Second pass: 2.61 / 2.62 / 3.42 Å are crystal facts on 1OKC; palmitoylcarnitine and carnitine are [schematic]. Teaching cargo is C16. Third pass: open “Disagreements” for ANT ≠ CACT, CATR ≠ cargo, static protein vs invert, and no EC.
Chemistry primer — antiport, not catalysis CACT is an inner-membrane MCF carrier. It does not make or break the acyl-carnitine ester. CPT1A made that ester on the OMM; CPT2 will undo it in the matrix. Gold H⁺ and blue nucleophile are not drawn — there is no catalytic event on this page. CATR is how ANT was crystallized, not how CACT works.
Words used on screen — fold analog · CATR · invert Fold analog — the mesh is bovine ANT1; CACT has no PDB. CATR — carboxyatractyloside, a named inhibitor occupancy. Invert — compiled MCF c/m reorientation drawn as a label on a static protein, not a morph. Arg79 ★ — PDB id on this ANT frame; not a CACT catalytic residue.

Legend & Fidelity

Mechanism fidelity — measured vs. inferred The measured layer: 1OKC (2.20 Å) bovine ANT1 + CATR; Arg79 NH2 ⋯ CXT O23 = 2.61 Å; Asp231 OD1 ⋯ CXT O21 = 2.62 Å; Lys22 NZ ⋯ Arg79 NH2 = 3.42 Å. The inferred layer ([schematic]): palmitoylcarnitine, L-carnitine, c→m invert label, cargo leave. Binding order is compiled staging, not a kinetic fit. The protein mesh is static. Schematic cargo Å are not geomClaims.
Disagreements on record (a) Gene. 1OKC is ANT1 (P02722 / SLC25A4), not CACT (O43772 / SLC25A20). CACT has no PDB. (b) CATR ≠ cargo. Carboxyatractyloside is an inhibitor, not acylcarnitine. (c) Static protein vs invert. 1OKC is the CATR-locked c-state; the m-state is not this crystal. (d) No EC. This is a carrier, not an enzyme. (e) ANT nucleotide transport is not shown. (f) Cardiolipin in 1OKC is not this cartoon. (g) Concerted vs split invert/release — this page splits ② then ③ then ④ for 1-event/1-step teaching.
Regulation — inhibitors · deficiency Atractyloside / carboxyatractyloside lock ANT from the IMS (this crystal). Bongkrekic acid locks from the matrix — not this occupancy. CACT deficiency (SLC25A20) is a fatty-acid oxidation disorder, named, not simulated. This mesh is not human CACT.Source: UniProt O43772 · PDB 1OKC
Kinetics scope (no measured timecourse on this page) One acylcarnitine / carnitine exchange event is drawn, not a steady-state run. Compiled transport rates are not re-asserted here — no measured k_cat/K_m on this page [schematic]. Pair with a transport chapter.Source: UniProt O43772 — no k_cat/K_m re-asserted
Sequence Human CACT UniProt O43772 · NCBI Gene 788 (no PDB). This screen uses bovine ANT1 numbering (Arg79 on 1OKC). Chain A. Cα 2–293.
Simulation map — what you see is what is written Setup = 1OKC cavity with CATR (opaque, no autoplay). ① schematic palmitoylcarnitine moves in from the IMS. ② slow-mo invert label on a static protein. ③ palmitoylcarnitine leaves to the matrix. ④ free carnitine enters from the matrix and leaves to the IMS. Only these events move.
Sources — bibliography of this page S1 — PDB 1OKC: bovine ANT1 + CATR, 2.20 Å — public coordinates; measured Arg79 NH2⋯CXT O23 = 2.61 Å · Asp231 OD1⋯CXT O21 = 2.62 Å · Lys22 NZ⋯Arg79 NH2 = 3.42 Å S2 — Pebay-Peyroula et al., Nature 2003, PMID:14603310 — ANT·CATR structure S3 — Sequence: UniProt O43772 (human CACT, no PDB) · NCBI Gene 788 · ANT1 P02722 S4 — CACT charged motifs: Giangregorio et al., J Biol Chem 2010, PMID:20347717 — compiled onto this ANT frame S5 — Kinetics: UniProt O43772 — no k_cat/K_m re-asserted on this page

› Backbones and ligand poses are taken directly from the listed PDB entries, superposed into one common frame. Where no crystalline state exists for a step (e.g., palmitoylcarnitine, carnitine, carrier invert, product release), the pose is drawn schematically and labeled as such in the narration. CATR is an inhibitor occupancy, not cargo.

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