The structure and polymerase-recognition mechanism of the crucial adaptor protein AND-1 in the human replisome [DNA and Chromosomes]

DNA replication in eukaryotic cells is performed by a multi-protein complex called the replisome, which consists of helicases, polymerases and adaptor molecules. Human acidic nucleoplasmic DNA-binding protein 1 (AND-1), also known as WD repeat and HMG-box DNA binding protein 1 (WDHD1), is an adaptor molecule crucial for DNA replication. While structural information for the AND-1 yeast ortholog is available, the mechanistic details for how human AND-1 protein anchors the lagging-strand DNA polymerase α (Pol α) to the DNA helicase complex (Cdc45-MCM2-7-GINS, CMG) await elucidation. Here, we report the structures of the N-terminal WD40 and SepB domains of human AND-1, as well as a biochemical analysis of the C-terminal HMG domain. We show that AND-1 exists as a homo-trimer mediated by the SepB domain. Mutant study results suggested that a positively charged groove within the SepB domain provides binding sites for Pol α. Different from its ortholog protein in budding yeast, human AND-1 is recruited to the CMG complex mediated by unknown participants other than GINS. In addition, we show that AND-1 binds to DNA in vitro, using its C-terminal HMG domain. In conclusion, our findings provide important insights into the mechanistic details of human AND-1 function, advancing our understanding of replisome formation during eukaryotic replication.

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