Coronavirus Update

The CMI COVID-19 Plan summarizes the changes implemented at CMI to maintain social distancing, enhance safety and accomodate CMI users. 

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 offers training and access to instruments for Isothermal Titration Calorimetry (ITC)Surface Plasmon Resonance (SPR)Biolayer Interferometry (BLI)Differential Scanning Fluorimetry (DSF)Circular Dichroism (CD)Light Scattering: size-exclusion chromatography with multi-angle light scattering (SEC-MALS) and Dynamic Light Scattering (DLS), and MicroScale Thermophoresis (MST)

The CMI offers data collection services for the characterization of protein secondary structure, mass and oligomeric state, polydispersity, aggregation state, hydrodynamic radius, and thermal stability.  Using a library developed in the lab of Andrew Kruse, the CMI is also offering yeast surface display nanobody selections services.

Recent CMI User Publications

Duncan-Lowey B. Effectors of Cell Death in Bacterial Antiphage Defense. 2022;Abstract
Bacteria encode many systems to detect and respond to infection with bacteriophages. Cyclic-oligonucleotide based antiphage signaling systems (CBASS) are widespread antiviral systems encoded in approximately 10% of bacterial genomes. Upon infection of CBASS-encoding bacteria, nucleotide second messengers are synthesized and can diffuse throughout the cell to bind diverse effector proteins. We use structural and biochemical methods to characterize effector proteins that specifically recognize nucleotide second messengers and are activated to induce cell death. Once this abortive infection system is activated, the effector proteins kill the bacterial host before the phage is able to replicate, thereby halting phage infection. We characterize one family of effectors, Cap4 proteins, that use a SAVED domain to specifically recognize nucleotide second messengers and are then activated to kill the cell through the indiscriminate cleavage of double-stranded DNA. These data highlight SAVED domains as widespread ligand-binding domains found in many CBASS effectors and revealed an evolutionary connection between CBASS and CRISPR immunity. We also characterized effector proteins that contain transmembrane domains, revealing that they target the inner membrane to induce cell death after phage infection. These data highlight membrane disruption as a widespread strategy to induce cell death in CBASS immunity. We further characterize one family of transmembrane effectors, Cap15 proteins, which we show use a minimal β-barrel domain to recognize nucleotide second messengers. Together, these studies begin to characterize diverse CBASS effectors that fulfill two requirements: 1. specific recognition of nucleotide second messengers, either by SAVED or β-barrel domains and 2. the induction of cell death, either through destruction of nucleic acids by Cap4 nucleases or inner membrane disruption by Cap15 transmembrane effectors. These data support an emerging model where CBASS effectors use a modular domain architecture to sense second messengers and induce cell death to halt phage replication.
Velarde JJ, Piai A, Lichtenstein IJ, Lynskey NN, Chou JJ, Wessels MR. Structure of the Streptococcus pyogenes NAD Glycohydrolase Translocation Domain and Its Essential Role in Toxin Binding to Oropharyngeal Keratinocytes. J Bacteriol 2022;204(1):e0036621.Abstract
The emergence and continued dominance of a Streptococcus pyogenes (group A Streptococcus, GAS) M1T1 clonal group is temporally correlated with acquisition of genomic sequences that confer high level expression of cotoxins streptolysin O (SLO) and NAD+-glycohydrolase (NADase). Experimental infection models have provided evidence that both toxins are important contributors to GAS virulence. SLO is a cholesterol-dependent pore-forming toxin capable of lysing virtually all types of mammalian cells. NADase, which is composed of an N-terminal translocation domain and C-terminal glycohydrolase domain, acts as an intracellular toxin that depletes host cell energy stores. NADase is dependent on SLO for internalization into epithelial cells, but its mechanism of interaction with the cell surface and details of its translocation mechanism remain unclear. In this study we found that NADase can bind oropharyngeal epithelial cells independently of SLO. This interaction is mediated by both domains of the toxin. We determined by NMR the structure of the translocation domain to be a β-sandwich with a disordered N-terminal region. The folded region of the domain has structural homology to carbohydrate binding modules. We show that excess NADase inhibits SLO-mediated hemolysis and binding to epithelial cells in vitro, suggesting NADase and SLO have shared surface receptors. This effect is abrogated by disruption of a putative carbohydrate binding site on the NADase translocation domain. Our data are consistent with a model whereby interactions of the NADase glycohydrolase domain and translocation domain with SLO and the cell surface increase avidity of NADase binding and facilitate toxin-toxin and toxin-cell surface interactions. IMPORTANCE NADase and streptolysin O (SLO) are secreted toxins important for pathogenesis of group A Streptococcus, the agent of strep throat and severe invasive infections. The two toxins interact in solution and mutually enhance cytotoxic activity. We now find that NADase is capable of binding to the surface of human cells independently of SLO. Structural analysis of the previously uncharacterized translocation domain of NADase suggests that it contains a carbohydrate binding module. The NADase translocation domain and SLO appear to recognize similar glycan structures on the cell surface, which may be one mechanism through which NADase enhances SLO pore-forming activity during infection. Our findings provide new insight into the NADase toxin and its functional interactions with SLO during streptococcal infection.
Harvey EP, Shin J-E, Skiba MA, Nemeth GR, Hurley JD, Wellner A, Shaw AY, Miranda VG, Min JK, Liu CC, Marks DS, Kruse AC. An in silico method to assess antibody fragment polyreactivity [Internet]. bioRxiv 2022; Publisher's VersionAbstract
Antibodies are essential biological research tools and important therapeutic agents, but some exhibit non-specific binding to off-target proteins and other biomolecules. Such polyreactive antibodies compromise screening pipelines, lead to incorrect and irreproducible experimental results, and are generally intractable for clinical development. We designed a set of experiments using a diverse na{\"ıve synthetic camelid antibody fragment (‘nanobody’) library to enable machine learning models to accurately assess polyreactivity from protein sequence (AUC > 0.8). Moreover, our models provide quantitative scoring metrics that predict the effect of amino acid substitutions on polyreactivity. We experimentally tested our model’s performance on three independent nanobody scaffolds, where over 90% of predicted substitutions successfully reduced polyreactivity. Importantly, the model allowed us to diminish the polyreactivity of an angiotensin II type I receptor antagonist nanobody, without compromising its pharmacological properties. We provide a companion web-server that offers a straightforward means of predicting polyreactivity and polyreactivity-reducing mutations for any given nanobody sequence.Competing Interest StatementC.C.L is a co-founder of K2 Biotechnologies Inc., which applies continuous evolution technologies to antibody engineering. D.S.M. is an advisor for Dyno Therapeutics, Octant, Jura Bio, Tectonic Therapeutic and Genentech, and is a co-founder of Seismic Therapeutic. A.C.K. is a co-founder and consultant for Tectonic Therapeutic and Seismic Therapeutic and for the Institute for Protein Innovation, a non-profit research institute.

CMI News

The CMI Welcomes Kayleigh Fay

June 8, 2021
Kayleigh Fay, MS, has joined the team at the CMI as a research assistant.  She'll be working on launching protein quality data collection services and helping with core maintenance.