CHARACTERIZATION OF THE QUATERNARY STRUCTURE AND CONFORMATIONAL PROPERTIES OF THE HUMAN STEM-CELL INHIBITOR PROTEIN-LD78 IN SOLUTION

The human LD78 protein (sometimes referred to as human macrophage infl ammatory protein-1alpha) has been shown to protect multipotential hemo poietic stem cells from the effects of cytotoxic agents. Administratio n of the recombinant stem cell inhibitor molecule LD78 as an adjunct t o chemotherapy has potential clinical benefit in reducing or preventin g the neutropenia associated with this treatment. At physiological ion ic strength, the 8-kDa LD78 molecule exists as soluble, heterogeneous, multimeric complexes of mass ranging from 100 to >250 kDa. The hydrod ynamic and structural properties of LD78 have been determined in vario us buffer solutions using analytical ultracentrifugation, circular dic hroism, and fluorescence spectroscopy. The results demonstrate that de fined, homogeneous monomer and tetramer forms of LD78 can be prepared which display distinct conformational properties. The combined use of hydrodynamic and spectroscopic analysis provides an insight into the p athway and molecular mechanics of LD78 self-association.