Molecular Mechanisms of Cell Cycle Regulation and Cancer Seth Rubin, Chemistry and Biochemistry The Rubin laboratory uses a variety of structural and biochemical techniques to investigate the molecular mechanisms that control the eukaryotic cell cycle. The aim is to elucidate detailed molecular pictures of protein-protein interactions and how these interactions are regulated by structural and chemical modifications. Improper regulation of these protein interaction networks is commonly associated with aberrant cell proliferation and cancer. (Keywords: structural biology, chemistry and biochemistry, cell cycle, cancer, protein chemistry, nuclear magnetic resonance (NMR), x-ray crystallography)

Cell growth and division are carefully coordinated by a shifting network of biomolecular interactions.  Protein interactions regulate enzymatic activities responsible for key cell cycle events such as DNA replication, chromosome segregation, and cytokinesis.  These events have strict spatial and temporal requirements for proper cell cycle function, and deregulation of protein interaction networks is commonly associated with aberrant cell proliferation and cancer.   Understanding mechanisms of cell cycle control requires a detailed molecular picture of protein-protein interactions and how these interactions regulate enzymatic function and cellular structure. 

Our laboratory seeks to elucidate the biochemical determinants of protein interaction affinity and specificity and how these factors are affected by regulatory modifications to protein composition and structure.  To this end, a number of structural and biochemical techniques, particularly x-ray crystallography and nuclear magnetic resonance, are applied to attain atomic resolution structures of protein complexes and to learn in molecular detail how structural changes and chemical modifications affect biological function. 

The x-ray crystal structure of an E2F-DP-Rb ternary complex reveals the details of the protein-protein interactions at atomic resolution.

Molecular Mechanisms Regulating the Retinoblastoma Tumor Suppressor Protein

One specific area of research in our laboratory studies proteins that control entry into the S phase of the cell cycle.  Members of the E2F family of transcription factors activate genes required for DNA synthesis and cell cycle progression.  The retinoblastoma (Rb) and related “pocket proteins” bind and inhibit E2F until the cell is ready to begin S phase.  At this point, Rb is phosphorylated by a protein kinase at multiple sites, E2F is released, and genes required for DNA synthesis and cell division are transcribed. 

The primary goal of our studies is to use atomic resolution structures and biophysical measurements of binding affinity to characterize the molecular interactions that stabilize the Rb-E2F complex and to understand how phosphorylation changes these interactions such that the complex dissociates.  Ongoing research also aims to reveal mechanisms of specificity in molecular recognition of particular phosphorylation sites by the kinases and phosphatases that regulate Rb.  We have recently begun pursuing structures of Rb in complex with other transcriptional regulatory proteins, including histone and chromatin modifying enzymes, to reveal the mechanism of how these repressive complexes assemble and dissociate upon Rb phosphorylation.

Protein Interaction Specificity in the Anaphase Promoting Complex