The disordered PCI‐binding human proteins CSNAP and DSS1 have diverged in structure and function

Abstract

Intrinsically disordered proteins (IDPs) regularly constitute components of larger protein assemblies contributing to architectural stability. Two small, highly acidic IDPs have been linked to the so-called PCI complexes carrying PCI-domain subunits, including the proteasome lid and the COP9 signalosome. These two IDPs, DSS1 and CSNAP, have been proposed to have similar structural propensities and functions, but they display differences in their interactions and interactome sizes. Here we characterized the structural properties of human DSS1 and CSNAP at the residue level using NMR spectroscopy and probed their propensities to bind ubiquitin. We find that distinct structural features present in DSS1 are completely absent in CSNAP, and vice versa, with lack of relevant ubiquitin binding to CSNAP, suggesting the two proteins to have diverged in both structure and function. Our work additionally highlights that different local features of seemingly similar IDPs, even subtle sequence variance, may endow them with different functional traits. Such traits may underlie their potential to engage in multiple interactions thereby impacting their interactome sizes.

The C-terminal tail of CSNAP attenuates the CSN complex

“…The C-terminal tail of CSNAP forms the main interaction region with the CSN complex In solution, CSNAP is an intrinsically unstructured protein, with a slight tendency to form an extended structure in its C-terminus (25). Within the context of the intact complex, however, the conformation of this subunit is unknown.…”

CDK2 and CDK4: Cell Cycle Functions Evolve Distinct, Catalysis-Competent Conformations, Offering Drug Targets

“…CSPs were subsequently determined by comparing the chemical shifts of the kinase in its free form with those in the cyclin-bound form. For each residue, we calculate the CSP (Δδ) between the CDK monomer and its cyclin-bound state using the formula: normalΔ δ = normalΔ δ H 2 + false( 0.154 × normalΔ δ N ) 2 , where Δδ H and Δδ N are the changes in the chemical shift of proton and nitrogen on the backbone of an amino acid, respectively, and 0.154 is the scaling factor. , …”

“…where Δδ H and Δδ N are the changes in the chemical shift of proton and nitrogen on the backbone of an amino acid, respectively, and 0.154 is the scaling factor. 35,38…”

CRISPR/Cas9-Targeted Disruption of Two Highly Homologous Arabidopsis thaliana DSS1 Genes with Roles in Development and the Oxidative Stress Response

“…DSS1 from different species has an alpha helix at the C-terminus end and two conserved acidic regions with a poorly conserved linker between them [3]. DSS1 protein without a helix complements the Schizosaccharomyces pombe dss1 mutant phenotype; accordingly, most bindings to DSS1 occur in the disordered region [7]. Its wide range of functions is manifested in its participation in the ubiquitin-26S proteasome system [8][9][10], the breast cancer 2 (BRCA2)-DNA repair complex [11][12][13], the pre-mRNA splicing complex [14] and the transcription-export-2 (TREX-2) complex [15].…”

“…In addition, the small acidic DSS1 protein has been shown to mimic DNA and to reduce the affinity of the replication protein A (RPA) for single-stranded DNA in exchange for RAD51 loading to single-strand DNA during repair [23]. In the HR machinery, DSS1 is likely to form protein complexes that do not contain PCI domains [7].…”