Aldolase Isozymes It has become increasingly clear that the enzyme fructose-1,6-(bis)phosphate aldolase (aldolase) plays crucial roles in the cell in addition to its well-known function in glycolysis and gluconeogenesis. These "moonlighting" cellular functions include the formation of complexes with such seemingly diverse targets as the actin cytoskeleton, parasitic adhesion proteins, glucose transporters, other glycolytic enzymes, and the S100 Ca2+ binding proteins, some of which are associated with metastatic tumor progression. In addition, the formation of aldolase complexes may affect aldolase catalytic activity, thus linking the metabolic functions of the enzyme with its cellular roles./td> Together with the Tolan lab, Boston University, we have shown that the differences in catalytic and binding modes among the three vertebrate aldolase isozymes reside in isozyme specific residues (ISRs) for each enzyme. These ISRs lie in surface patches distant from the active site. From the X-ray crystallographic structures of all three isozymes, there are no clear differences at the active site. Together with the laboratory of William Lehman, Boston University School of Medicine, we have determined, via helical-reconstruction and single particle analysis of electron micrographs (EM), a low-resolution structure of aldolase bound to F-actin. The structure shows that aldolase binds regularly to actin in a manner similar to other actin binding proteins such as myosin subfragment 1. This structure reveals the mode of binding: aldolase binds to actin via two monomers of the aldolase homotetramer and two actin monomers. We hypothesize that this frees the two remaining aldolase monomers for interaction with a second binding partner, thus allowing aldolase to function as a "molecular adaptor". Continuing studies in the Allen lab explore the complexes formed by aldolase at the atomic and molecular level and their possible cellular functions. Although a great deal of information exists at the molecular level on the structure and function of metabolic enzymes as catalysts, there is a disconnection between this level and that of overall cellular function. The Allen lab seeks to bridge this gap by quantifying interactions that have been observed on the cellular level and providing molecular structures for these multiprotein complexes. This work is funded by NIH grant GM 61606.