School of Life Science and Technology, Tokyo Institute of Technology, Yokohama, Japan.
Cell Biology Center, Institute of Innovative Research, Tokyo Institute of Technology, Yokohama, Japan.
Genes Cells. 2024 May;29(5):361-379. doi: 10.1111/gtc.13109. Epub 2024 Feb 25.
Constitutive heterochromatin is transcriptionally repressed and densely packed chromatin, typically harboring histone H3 Lys9 trimethylation (H3K9me3) and heterochromatin protein 1 (HP1). SUV420H2, a histone H4 Lys20 methyltransferase, is recruited to heterochromatin by binding to HP1 through its Heterochromatic Targeting Module (HTM). Here, we have identified three HP1 binding motifs within the HTM. Both the full-length HTM and its N-terminal region (HTM-N), which contains the first and second motifs, stabilized HP1 on heterochromatin. The intervening region between the first and second HP1 binding motifs in HTM-N was also crucial for HP1 binding. In contrast, the C-terminal region of HTM (HTM-C), containing the third motif, destabilized HP1 on chromatin. An HTM V374D mutant, featuring a Val374 to Asp substitution in the second HP1 binding motif, localizes to heterochromatin without affecting HP1 stability. These data suggest that the second HP1 binding motif in the SUV420H2 HTM is critical for locking HP1 on H3K9me3-enriched heterochromatin. HTM V374D, tagged with a fluorescent protein, can serve as a live-cell probe to visualize HP1-bound heterochromatin.
组成性异染色质是转录抑制的、紧密包装的染色质，通常含有组蛋白 H3 赖氨酸 9 三甲基化 (H3K9me3) 和异染色质蛋白 1 (HP1)。SUV420H2 是一种组蛋白 H4 赖氨酸 20 甲基转移酶，通过其异染色质靶向模块 (HTM) 与 HP1 结合而被招募到异染色质。在这里，我们已经在 HTM 中鉴定出三个 HP1 结合基序。全长 HTM 及其 N 端区域（HTM-N），包含第一和第二基序，稳定了异染色质上的 HP1。HTM-N 中第一和第二个 HP1 结合基序之间的间隔区对于 HP1 结合也至关重要。相比之下，HTM 的 C 端区域（HTM-C），包含第三个基序，在染色质上使 HP1 不稳定。HTM V374D 突变体在第二个 HP1 结合基序中具有 Val374 到 Asp 的取代，其特征是在不影响 HP1 稳定性的情况下定位于异染色质。这些数据表明，SUV420H2 HTM 中的第二个 HP1 结合基序对于将 HP1 锁定在富含 H3K9me3 的异染色质上至关重要。标记有荧光蛋白的 HTM V374D 可以作为活细胞探针，用于可视化 HP1 结合的异染色质。
