Texas Tech University
TTU HomeDepartment of Chemistry and Biochemistry Faculty Dr. Robert W. Shaw

Dr. Robert W. Shaw

Title:

Associate Professor

Education:

Ph.D., 1976, The Pennsylvania State University; Postdoctoral Study, Institute for Enzyme Research, University of Wisconsin, Madison

Research Area:

Biochemistry

Office:

Phone:

Email:

Chemistry 330-A

806-834-3804

Robert.Shaw@ttu.edu

 

Research Group

Principal Research Interests

Professor Shaw's research program involves the study of the structure and function of physiologically important metalloenzymes. Structures of the metal binding sites of these biological molecules are under investigation largely through the use of optical and electron paramagnetic resonance (EPR) spectroscopy. Mechanistic details of the functions of metal ions in these proteins are being studied through the use of spectroscopy coupled to rapid kinetic techniques in order to detect short-lived species such as reaction intermediates and enzyme complexes with substrates or inhibitors. Enzyme structure-function relationships are analyzed by site-directed mutagenesis combined with presteady-state spectroscopy and steady-state enzyme kinetic techniques.

Current interest is focused on the metallo-ß-lactamases purified from the pathogenic organism Bacillus cereus. ß-Lactamases catalyze the hydrolytic inactivation of ß-lactam antibiotics such as penicillins and cephalosporins and thereby constitute the major mechanism by which pathogenic bacteria become resistant to such antibiotics. ß-Lactam antibiotics are the most heavily prescribed antibacterial drugs in clinical use today.  In fact, three of the twenty most commonly prescribed drugs in the U. S. fall in this category.  No compounds are available that can inhibit the metallo-ß-lactamases and thereby allow the antibiotics to do their job of killing pathogenic bacteria. Clearly, understanding the reaction mechanisms of ß-lactamases is important to the pharmaceutical industry.

The structural gene for the B. cereus 5/B/6 ß-lactamase has been cloned into an Escherichia coli expression vector and techniques have been devised to purify the hyperexpressed B. cereus enzyme (both wild type and mutant forms) to homogeneity in very high (~90%) yield. Using site-directed mutagenesis techniques and this recombinant construct, a study of the relationship of protein structure to enzymatic function of this enzyme has begun. So far, forty four mutant forms of the enzyme have been expressed and 12 of these purified and characterized.

We have utilized the SELEX (Systematic Evolution of Ligands by Exponential Enrichment) technique to generate ss-, ds-DNA and RNA aptamaers of very different sequence that efficiently inhibit the metallo-ß-lactamase.  Experiments are currently underway to elucidate the details of how these compounds inhibit the antibiotic inactivation process.  A 10-residue ss-DNA has been found that very specifically and efficiently inhibits the metallo-ß-lactamase at nanomolar concentrations.  The ds-DNA and RNA aptamers are similarly effective.  Despite the sequence differences between these aptamers, they all appear to inhibit the metallo-ß-lactamase in essentially the same fashion.  Currently, we believe that the aptamers bind at or close enough to the active site metal ions as to either coordinate the metal directly or to otherwise force a change in the metal coordination sphere.

 

Representative Publications