This laboratory is interested in the relationship between protein sequence, structure and the mechanisms of protein folding and enzymatic reactions. Histidine Rich Proteins - The malaria parasite, Plasmodium falciparum, produces large amounts of several histidine rich proteins of unknown structure. Their high concentrations of histidine distort their circular dichroic spectra, so that, unlike those of normal proteins they cannot be interpreted in terms of secondary structures. We are reinvestigating the behavior of poly L-histidine as a function of pH and solvent additives, using modern methods of spectral deconvolution and analysis. We are establishing a set of reference spectra under defined conditions, which can be used in analysis of the structures of these unusual proteins. Structure of Tryptophan Synthase - (with S. Ashraf Ahmed and Edith Wilson Miles, LBP) We are investigating the conformational states of the tryptophan synthase alpha2/beta2 complex and of the separate alpha and beta subunits. We find that mutations, cosolvents and cations alter the structure and function. Our analysis of the effects of thermally induced unfolding of the alpha2/beta2 complex on the UV-visible spectra and activity show the presence of an inactive, partially unfolded intermediate. Structure of Mammalian Sulphotransferases. (with D. Marshall and W.B.Jakoby, LBM) During preparation of a cloned phenol sulphotransferase, two distinct forms of the enzyme were isolated. One form (B) behaved like enzyme previously isolated from rat liver; the second form (A) showed reduced activity in the sulphation reaction and was able to catalyze the transfer of sulphate without added cofactor, PAP (adenosine 3', 5' bisphosphate). Forms A and B can be interconverted by treatment with oxidized/reduced glutathione, DTNB or mercaptoethanol. This indicates the involvement of one or more disulphide bonds at the active site of the enzyme. Peptide mapping and HPLC are being used to locate these bond(s). Interaction of Amphotericin B with Membranes. (with R. A. Brutyan, LBM) The antifungal drug Amphotericin B undergoes a large enhancement in its CD spectrum on binding to membranes. It's activity is inhibited by the organic cation TEA, but the continued presence of optical activity rules out the possibility of dissociation as an explanation of this inhibition.
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