Fusion Protein‐Assisted Crystallization of Human SUMO1

Abstract

International audienceABSTRACT In this study, we employed a fusion protein‐assisted approach to crystallize human SUMO1, an essential covalent protein modifier that also interacts noncovalently with specific linear protein motifs called SUMO‐interacting motifs (SIMs). SUMO1 has been crystallized previously as part of various complexes but never in isolation. Our strategy involved fusing a variant of a known crystallization facilitator, the TELSAM domain, upstream of the folded part of the SUMO1 protein (residues 18–97). Following a simple purification strategy, we obtained a 2.05‐Å crystal structure of apo TELSAM‐SUMO1, with three distinct SUMO1 chains per asymmetric unit, two of which have an accessible pocket for binding to a SIM. The crystal structure is composed of the expected left‐handed helical filaments formed by TELSAM domains, with protruding SUMO1 molecules mediating connections within and between these filaments to stabilize a three‐dimensional lattice. Since the TELSAM fusion does not affect the SUMO:SIM interaction, as confirmed in solution, our construct may potentially be used to structurally characterize complexes formed between SUMO and SIM‐containing peptides. Neither does the TELSAM fusion interfere with the attachment of SUMO1 to substrates, potentially allowing for the creation of SUMOylated protein forms with improved crystallizability. The study represents a novel application of TELSAM‐assisted crystallization to a small protein of major biological relevance