Biochemical Properties of Naturally Occurring Human Bloom Helicase Variants

Abstract

Bloom syndrome helicase (BLM) is a RecQ-family helicase implicated in a variety of cellular 24 processes, including DNA replication, DNA repair, and telomere maintenance. Mutations in 25 human BLM cause Bloom syndrome (BS), an autosomal recessive disorder that leads to myriad 26 negative health impacts including a predisposition to cancer. BS-causing mutations in BLM 27 often negatively impact BLM ATPase and helicase activity. While BLM mutations that cause BS 28 have been well characterized both in vitro and in vivo, there are other less studied BLM 29 mutations that exist in the human population that do not lead to BS. Two of these non-BS 30 mutations, encoding BLM P868L and BLM G1120R, when homozygous, increase sister 31 chromatid exchanges in human cells. To characterize these naturally occurring BLM mutant 32 proteins in vitro, we purified the BLM catalytic core (BLMcore, residues 636-1298) with either the 33 P868L or G1120R substitution.