Bimodal conformations of SMC5/6 regulate molecular activities and anti-genotoxic functions

The National Institute of Environmental Health Sciences awarded Weill Medical College of Cornell University $100,228 on October 4, 2026, under the Environmental Health program (CFDA 93.113) to investigate how bimodal conformations of the SMC5/6 protein complex regulate molecular activities and anti-genotoxic functions.

The project will examine the functional mechanisms of SMC5/6 using in vitro and in vivo approaches in budding yeast, with particular focus on how two distinct conformational states—termed NSE4-neck and NSE6-neck—regulate the complex's biochemical activities of ATP hydrolysis and DNA binding. Aim 1 will characterize how these conformational states regulate biochemical activities, while Aim 2 will build on preliminary genetic findings to elucidate SMC5/6-mediated functions in DNA replication termination and repair intermediate removal. Understanding these mechanisms is intended to advance knowledge of how cells respond to environmental genotoxins and support the development of new disease treatments.

The award is classified as a Project Grant, an assistance type supporting investigator-initiated research. Performance occurs at Weill Medical College's location in New York, New York. The period of performance extends from October 4, 2026, through May 31, 2029.

Abstract

Humans are constantly exposed to environmental genotoxins, inducing DNA lesions that lead to mutations and diseases such as cancer and developmental defects. To preserve genome integrity, cells have evolved a highly conserved network of pathways to repair DNA lesions and manage DNA replication. In eukaryotes, a key member of this network is the conserved SMC5/6 complex, which has direct roles in DNA repair and replication. SMC5/6's functions are critical, as its dysfunction sensitizes cells to many genotoxins and devastating genome instability syndromes in humans. Despite its importance in genome maintenance, how SMC5/6 performs its anti- genotoxic functions is poorly understood. Uncovering the core principles by which SMC5/6 modulates its genomic functions is critical in understanding how cells respond to environmental genotoxins and in advancing new avenues for treating diseases. Our structural data have revealed two competing conformations of budding yeast SMC5/6 that are proposed to regulate its key activities of DNA binding and ATP hydrolysis. These conformations, termed the NSE4-neck and NSE6-neck states, are required to protect against genotoxic stress. Further, genetic tests have revealed that each conformational state is required for specific SMC5/6-mediated functions in DNA replication termination and repair intermediate removal. Thus, we hypothesize that the two SMC5/6 conformational states regulate the complex's key biochemical activities to enable distinct genome protection roles. To test this hypothesis, this project will investigate SMC5/6's functional mechanisms using a combination of in vitro and in vivo approaches in budding yeast. Aim 1's experiments will examine how the two distinct conformational states of SMC5/6 regulate its biochemical activities of ATP hydrolysis and DNA binding. Aim 2 will build on preliminary genetic findings suggesting that the NSE4-neck state of SMC5/6 is recruited to stalled replication forks at rdna sites to aid replication termination. We will test how the SMC5/6 NSE4-neck state impacts replication termination and SMC5/6 chromatin localization through genomic approaches. In aim 3, we will expand on previous work suggesting the NSE6-neck state of SMC5/6 modulates recombinational repair factors like SGS1 to aid in removing DNA repair intermediates. As such, we will test how perturbing the NSE6-neck state in cells affects SMC5/6-mediated repair intermediate removal and SGS1 modulation. These aims will reveal the mechanisms by which SMC5/6 drives its genome integrity functions to provide widespread genotoxin resistance. As SMC5/6 mutations cause genotoxin sensitivity and diseases such as genome instability syndromes, this research will guide the study of human SMC5/6 into its disease-causing mechanisms. This research plan will provide the F31 candidate strong training in the genome integrity field under the guidance of the sponsor DR. Xiaolan zhao, an expert in SMC5/6 biology and genome maintenance processes. Further, the candidate's network of committed mentors and collaborators will drive their progress in mastering multidisciplinary research approaches, developing mentoring skills, and cultivating strong communication skills.