Q4: Logical Deduction – Chromatin Remodeling and CHD2 Pathology A patient is identified with a de novo mutation that specifically disables the SNF2-like ATPase domain of the CHD2 protein while leaving its tandem chromodomains intact. Based on the biochemical roles of CHD subfamilies, deduce how this mutation alters nucleosome maturation and spacing. Contrast this with a hypothetical mutation that instead disables the chromodomains; which defect would more severely impair the protein’s ability to "recognize" the H3K4me2/3 active chromatin mark?

What happens when the SNF2-like ATPase domain of CHD2 is disabled but chromodomains remain intact?

Loss of spacing (cannot mobilize or slide nucleosomes) and maturation defect (cannot establish stable, well-ordered chromatin), leading to disorganized chromatin architecture.

What is the normal function of the SNF2-like ATPase domain in CHD2?

It is the catalytic "engine" coupling ATP hydrolysis to DNA movement. CHD2 remodels chromatin and assembles regularly spaced nucleosome arrays in an ATP-dependent manner.

Which mutation more severely impairs recognition of H3K4me2/3: ATPase domain or chromodomain?

Chromodomain mutation.

Why does a chromodomain mutation impair H3K4me2/3 recognition more severely than an ATPase mutation?

Because chromodomains are the specific molecular modules that recognize H3K4me2/3. ATPase mutant still binds the mark (via intact chromodomains) but cannot remodel. Chromodomain mutant loses the primary recruitment mechanism entirely.

What happens if the ATPase domain is disabled but chromodomains remain intact?

The protein can still recognize and bind H3K4me2/3 marks via intact chromodomains, but cannot perform remodeling work (spacing and maturation).

What is the overall conclusion comparing ATPase versus chromodomain mutations in CHD2?

ATPase defect halts mechanical function (spacing/maturation). Chromodomain mutation more severely impairs recognition of H3K4me2/3 because chromodomains are the specific modules for identifying that active chromatin signatu