Tousled-like kinase 2 targets ASF1 histone chaperones through client mimicry

Bertrand Simon,Guangda Shi,Clotilde Huet-Calderwood,Titus J Boggon,David A Calderwood,Benjamin E Turk,Hua Jane Lou

doi:10.1038/s41467-022-28427-0

Abstract

Tousled-like kinases (TLKs) are nuclear serine-threonine kinases essential for genome maintenance and proper cell division in animals and plants. A major function of TLKs is to phosphorylate the histone chaperone proteins ASF1a and ASF1b to facilitate DNA replication-coupled nucleosome assembly, but how TLKs selectively target these critical substrates is unknown. Here, we show that TLK2 selectivity towards ASF1 substrates is achieved in two ways. First, the TLK2 catalytic domain recognizes consensus phosphorylation site motifs in the ASF1 C-terminal tail. Second, a short sequence at the TLK2 N-terminus docks onto the ASF1a globular N-terminal domain in a manner that mimics its histone H3 client. Disrupting either catalytic or non-catalytic interactions through mutagenesis hampers ASF1 phosphorylation by TLK2 and cell growth. Our results suggest that the stringent selectivity of TLKs for ASF1 is enforced by an unusual interaction mode involving mutual recognition of a short sequence motifs by both kinase and substrate.

Highlights

Tousled-like kinases (TLKs) are nuclear serine-threonine kinases essential for genome maintenance and proper cell division in animals and plants
To determine whether residues selected by positional scanning peptide library (PSPL) are important in the context of an authentic tousled-like kinase 2 (TLK2) substrate, we mutated residues flanking ASF1b Ser[198], which conforms closely to the experimentally determined motif
We found that mutation of the −2 Glu, −1 Asn, or +1 Met residue of ASF1b-CT reduced phosphorylation by TLK2

Summary

Introduction

Tousled-like kinases (TLKs) are nuclear serine-threonine kinases essential for genome maintenance and proper cell division in animals and plants. A major function of TLKs is to phosphorylate the histone chaperone proteins ASF1a and ASF1b to facilitate DNA replicationcoupled nucleosome assembly, but how TLKs selectively target these critical substrates is unknown. Nucleosome assembly is a regulated multi-step process where deposition of a tetramer of histone 3 and 4 [(H3-H4)2] on DNA is followed by the addition of two histone (H2A-H2B) dimers[1]. These processes are controlled by histone chaperones and nucleosome assembly factors that bind histones, mediate their interactions with DNA, and modulate histone post-translational modifications[2]. ASF1 consists of an N-terminal 155-residue immunoglobulin-like domain (ASF1NT) followed by a presumably unstructured C-terminal tail[16,17,18]

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Conclusion