Call: (240) 314-6204
Call: (240) 314-6204
- Ph.D., Chemistry, University of Texas at Austin, 1990
- B.S., Electrical Engineering and Computer Science, MIT, 1979
Dr. Travis Gallagher’s research is focused on measurement strategies that provide atomic-level structural descriptions of proteins and their interactions. By combining diffraction-based methods with other biophysical tools, Dr. Gallagher develops methods for imaging and analysis of biomolecules. Of particular interest are proteins with applications as healthcare measurement standards, and their conformational dynamics. Immunotherapies, and especially antibodies (Abs), are key areas of biopharmaceutical development. These medicines depend crucially on verifiable stability and batch-to-batch reproducibility, creating a need for standards and reliable measurements.
Antibody (Ab) Structure
The NIST standard antibody (reference material 8671, also called NISTmAb) is enabling comparisons of measurements and protocols worldwide, and its value is largely due to its elaborate published characterization. Structural characterization includes high-resolution, all-atom crystal structures of its Fab and Fc fragments, prepared by papain cleavage. These structures (5k8a and 5vgp) have been combined with a modeled structure of the hinge region (based on the low-resolution precedent 1hzh and recent NIST-collected EM images) to produce a 3D model of the whole antibody. This model has 10445 non-hydrogen atoms, comprising all 1326 amino acids in four chains, and G1F/G0F glycans; it is available internally and is widely used as a reference model to support various Ab research projects at NIST.
Characterizing the Hinge
Flexibility is important to Abs' bivalent binding and signaling, and thus to biological function. The Ab hinge is responsible for most of this enormous flexibility, yet it is correspondingly difficult to characterize the hinge structurally. We have obtained crystals of an F(ab)2 double-Fab fragment, produced by pepsin, which cleaves in the lower hinge. No such structure has yet been reported; these crystals contain an almost complete hinge and offer the possibility of providing new structural data for the hinge, and thus for Ab conformational dynamics.
As a human IgG1 monoclonal Ab, NISTmAb has about eight well-characterized ligand proteins, including proteins A and G, and Fc receptors. Most of these are, or can be truncated into, small proteins. These, along with antigen constructs, provide a toolbox for attaching labels and for forming double-ligand constructs as conformational probes. One of these constructs links a minimal (53-residue) antigen with metallothionein to form a heavy-metal label for SAXS and EM imaging. Another construct links two antigens by means of a variable linker, forming a probe of how close the paratopes can approach each other, an indirect method of measuring Ab flexibility.
Mapping Conformation Space
What is the range of antibody conformational excursions, and what is the best way to measure it? Mathematical and computational tools are being developed to answer these questions. In geometric terms, what is the dimensionality of antibody conformation space? What is a computationally efficient way to parameterize it? Are there highly and sparsely populated regions of this space? Are there antibody conformations associated with aggregation, with key biological events, or with pathology? Is there a conformational code in antibody signaling?