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← Theoretical A

Q9 — ATAD1 Mitochondrial ATPase (Cryo-EM Study)

Theoretical A Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Protein Structure, Folding & Function

Cryo-EM is a modern structural study technique that works by averaging multiple low-quality electron micrographs; cryo-EM generates high-quality structural maps. It offers flexibility by accommodating various molecular sizes and capturing multiple conformations. The structure and mechanism of ATAD1, a mitochondrial homohexamer protein, were resolved using cryo-EM. The protein’s function was then determined using the structural data and fluorescent assays.

Panel A: a colored cryo-EM density map of the ATAD1 hexamer with subunits M1-M5 labeled ATP-bound and M6 labeled Apo/unclear. Panel B: a top-view cartoon of the hexamer emphasizing each subunit’s C-terminal alpha helix and a black curve representing the substrate polypeptide threading through the pore. Panel C: the central pore’s interacting aromatic residues (W166, Y167) around the black substrate chain. Panel D: fluorescence microscopy of Gos28, ATAD1, and MitoTracker channels for wild-type ATAD1 and the E193Q mutant. Figure 1. A Density map of the average of all conformations obtained by electron microscopy. B Top view of the molecular model of ATAD1 hexamer emphasizing C-terminal alpha-helices, with a black curve representing the polypeptide chain substrate. C The structure of the central pore with its substrate (black) and all interacting amino acids (colored residues). D Fluorescent microscopy assay for wild-type ATAD1 and with mutation E193Q (at position 193, Glu → Gln), Gos28 is the hypothetical target, MitoTracker is a mitochondrial fluorescent marker, the red arrow points to one mitochondrion.

On your answer sheet, indicate “T” for true statements and “F” for false ones.

A. Given that the density map contains an unclear M6 subunit, at any moment only one of the ATAD1 subunits is flexible.
B. C-terminal alpha helices shown on the molecular model are made entirely from hydrophobic amino acids.
C. Change of charge due to mutation E193Q affects the physical interaction of position 193 with the substrate.
D. ATAD1 translocates proteins mislocalized into the matrix of the mitochondria.
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Question reproduced from IBO 2024, Theoretical Exam Part A, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)