• CMI SEC-MALS system
  • CMI Jasco J815 CD instrument
  • CMI MST and ITC instruments
  • CMI SPR and BLI instruments
  • CMI Laboratory

Center for Macromolecular Interactions

Welcome to the Center for Macromolecular Interactions (CMI) in the department of Biological Chemistry and Molecular Pharmacology at Harvard Medical School.  Our mission is to enhance basic research in the HMS community by providing scientific consultation, training and access to shared biophysical instruments for the characterization and analysis of macromolecules and their complexes.

The facility currently includes instruments for Isothermal Titration Calorimetry (ITC), Surface Plasmon Resonance (SPR), Biolayer Interferometry (BLI), Differential Scanning Fluorimetry (DSF), Circular Dichroism (CD), Analytical Size Exclusion Chromatography with Multi-Angle Light Scattering (SEC-MALS), and MicroScale Thermophoresis (MST).   To learn more about technologies available, visit the CMI Instruments Page.

 

Recent CMI User Publications

Song D, Rodrigues K, Graham TGW, Loparo JJ. A network of cis and trans interactions is required for ParB spreading. Nucleic Acids Res 2017;Abstract
Most bacteria utilize the highly conserved parABS partitioning system in plasmid and chromosome segregation. This system depends on a DNA-binding protein ParB, which binds specifically to the centromere DNA sequence parS and to adjacent non-specific DNA over multiple kilobases in a phenomenon called spreading. Previous single-molecule experiments in combination with genetic, biochemical and computational studies have argued that ParB spreading requires cooperative interactions between ParB dimers including DNA bridging and possible nearest-neighbor interactions. A recent structure of a ParB homolog co-crystallized with parS revealed that ParB dimers tetramerize to form a higher order nucleoprotein complex. Using this structure as a guide, we systematically ablated a series of proposed intermolecular interactions in the Bacillus subtilis ParB (BsSpo0J) and characterized their effect on spreading using both in vivo and in vitro assays. In particular, we measured DNA compaction mediated by BsSpo0J using a recently developed single-molecule method to simultaneously visualize protein binding on single DNA molecules and changes in DNA conformation without protein labeling. Our results indicate that residues acting as hubs for multiple interactions frequently led to the most severe spreading defects when mutated, and that a network of both cis and trans interactions between ParB dimers is necessary for spreading.
Severson E, Arnett KL, Wang H, Zang C, Taing L, Liu H, Pear WS, Shirley Liu X, Blacklow SC, Aster JC. Genome-wide identification and characterization of Notch transcription complex-binding sequence-paired sites in leukemia cells. Sci Signal 2017;10(477)Abstract
Notch transcription complexes (NTCs) drive target gene expression by binding to two distinct types of genomic response elements, NTC monomer-binding sites and sequence-paired sites (SPSs) that bind NTC dimers. SPSs are conserved and have been linked to the Notch responsiveness of a few genes. To assess the overall contribution of SPSs to Notch-dependent gene regulation, we determined the DNA sequence requirements for NTC dimerization using a fluorescence resonance energy transfer (FRET) assay and applied insights from these in vitro studies to Notch-"addicted" T cell acute lymphoblastic leukemia (T-ALL) cells. We found that SPSs contributed to the regulation of about a third of direct Notch target genes. Although originally described in promoters, SPSs are present mainly in long-range enhancers, including an enhancer containing a newly described SPS that regulates HES5 expression. Our work provides a general method for identifying SPSs in genome-wide data sets and highlights the widespread role of NTC dimerization in Notch-transformed leukemia cells.
Li J, Su Y, Xia W, Qin Y, Humphries MJ, Vestweber D, Cabañas C, Lu C, Springer TA. Conformational equilibria and intrinsic affinities define integrin activation. EMBO J 2017;36(5):629-645.Abstract
We show that the three conformational states of integrin α5β1 have discrete free energies and define activation by measuring intrinsic affinities for ligand of each state and the equilibria linking them. The 5,000-fold higher affinity of the extended-open state than the bent-closed and extended-closed states demonstrates profound regulation of affinity. Free energy requirements for activation are defined with protein fragments and intact α5β1 On the surface of K562 cells, α5β1 is 99.8% bent-closed. Stabilization of the bent conformation by integrin transmembrane and cytoplasmic domains must be overcome by cellular energy input to stabilize extension. Following extension, headpiece opening is energetically favored. N-glycans and leg domains in each subunit that connect the ligand-binding head to the membrane repel or crowd one another and regulate conformational equilibria in favor of headpiece opening. The results suggest new principles for regulating signaling in the large class of receptors built from extracellular domains in tandem with single-span transmembrane domains.
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Latest News

Demo: SEC-MALS integrated HPLC control software

December 7, 2016

Wyatt has launched HPLC management software that integrates control of Agilent chromatography systems into Astra 7.  We'll be testing this software over the next few months.  Talk to Kelly if you'd like to try it.

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