Structure of KAP1 tripartite motif identifies molecular interfaces required for retroelement silencing

Guido A Stoll,Shun-Ichiro Oda,Zheng-Shan Chong,Minmin Yu,Stephen H Mclaughlin,Yorgo Modis

doi:10.1073/pnas.1901318116

Abstract

Transcription of transposable elements is tightly regulated to prevent genome damage. KRAB domain-containing zinc finger proteins (KRAB-ZFPs) and KRAB-associated protein 1 (KAP1/TRIM28) play a key role in regulating retrotransposons. KRAB-ZFPs recognize specific retrotransposon sequences and recruit KAP1, inducing the assembly of an epigenetic silencing complex, with chromatin remodeling activities that repress transcription of the targeted retrotransposon and adjacent genes. Our biophysical and structural data show that the tripartite motif (TRIM) of KAP1 forms antiparallel dimers, which further assemble into tetramers and higher-order oligomers in a concentration-dependent manner. Structure-based mutations in the B-box 1 domain prevent higher-order oligomerization without significant loss of retrotransposon silencing activity, indicating that, in contrast to other TRIM-family proteins, self-assembly is not essential for KAP1 function. The crystal structure of the KAP1 TRIM dimer identifies the KRAB domain binding site in the coiled-coil domain near the dyad. Mutations at this site abolished KRAB binding and transcriptional silencing activity of KAP1. This work identifies the interaction interfaces in the KAP1 TRIM responsible for self-association and KRAB binding and establishes their role in retrotransposon silencing.

Highlights

Transcription of transposable elements is tightly regulated to prevent genome damage
The presence of 2 or more domains capable of oligomerization independently can lead to polymerization of tripartite motif (TRIM) into lattices or scaffolds [25, 27, 28], but it remains unclear whether this applies to KAP1
Size-exclusion chromatography coupled with multiangle light scattering (SECMALS) showed that the RING domain was monomeric at concentrations ranging from 0.1 to 1.1 mM (1 to 10.5 g L−1; Fig. 1B)

Summary

Introduction

Transcription of transposable elements is tightly regulated to prevent genome damage. Structure-based mutations in the B-box 1 domain prevent higher-order oligomerization without significant loss of retrotransposon silencing activity, indicating that, in contrast to other TRIM-family proteins, self-assembly is not essential for KAP1 function. The crystal structure of the KAP1 TRIM dimer identifies the KRAB domain binding site in the coiled-coil domain near the dyad. Mutations at this site abolished KRAB binding and transcriptional silencing activity of KAP1. Retrovirus genomes that integrate into the genome of germline cells are inherited by future generations These endogenous retroviruses (ERVs) can retain the ability to replicate by transcriptional amplification and expression of the viral reverse transcriptase and integrase, which convert the genome transcripts into DNA and reintegrate it into the host genome. TE-derived proteins catalyze V(D)J recombination [4] and syncytiotrophoblast fusion in placental development [1, 5]

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Results

Conclusion