Our projects involving the structures and functions of soluble enzymes evolved from Connie’s postdoctoral work on the X-ray crystal structure of phosphoglucose isomerase (PGI). PGI catalyzes the second step in glycolysis, the interconversion of glucose-6-phosphate and fructose-6-phosphate. It is also the same protein as the extracellular cytokines (1) autocrine motility factor, (2) neuroleukin, and (3) differentiation and maturation mediator. PGI binding to a cell-surface receptor on target cells causes leukemia cell differentiation and changes in tumor cell motility. More recently, it was also found to be the self antigen in the best mouse model of rheumatoid arthritis. Our current research involves the molecular mechanisms of mammalian PGI and two other sugar isomerases and a computer-based analysis of disease-causing amino acid substitutions.

Structures and molecular mechanisms of PGI and other phosphosugar isomerases. Members of the Jeffery lab have solved five additional X-ray crystal structures of mammalian PGI and used them to develop a detailed model of its multistep catalytic mechanism. Ongoing projects include determining the X-ray crystal structures and mechanisms of two phosphosugar isomerase enzymes from the pathogens Pseudomonas aeruginosa and Trypanosoma brucei. P. aeruginosa causes chronic, serious lung infections in patients with cystic fibrosis (CF) that are a major cause of the decreased life span of CF patients. We are studying the bifunctional enzyme phosphomannose isomerase/GDP-D-mannose pyrophosphorylase, which is one of the proteins involved in the infection process. Another enzyme we are studying is from T. brucei, the causative agent in sleeping sickness. In the host's bloodstream, trypanosomes depend on the enzymes of glycolysis for energy production, so inhibitors of those enzymes would be good lead compounds for the design of therapeutics. It is hoped that novel inhibitors of the enzymes resulting from our research will serve as lead compounds for the future development of drugs to fight Pseudomonas and Trypanosoma infections.

Computer-based analysis of disease-causing amino acid substitutions. Another ongoing project is a computer-based analysis of the structures of proteins in which single nucleotide polymorphisms (SNPs) cause single amino acid substitutions that lead to genetic disease. A current method being used to identify the causes of genetic diseases is to identify SNPs that differ between affected and unaffected individuals. However, this method can identify differences in the nucleotide sequences of multiple genes, and it can be difficult to determine which differences are involved in the disease. We are studying the structures of several proteins in which there are known SNPs that encode amino acid substitutions that cause genetic disease. The study has implications in protein folding, stability, and evolution, and as well as in predicting the importance of single nucleotide polymorphisms.